cro manual

Oscilloscope Demonstrator Trainer ST2001E

Operating Manual Ver 1.1

An ISO 9001 : 2000 company

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ST2001E

Scientech Technologies Pvt. Ltd. 2

ST2001E


Oscilloscope Demonstrator Trainer ST2001E

Table of Contents 1. Introduction 4

2. Technical Specifications 5

3. Oscilloscope Controls 6

• Front Panel Controls 6

• Controls on PCB 7 4. Test Point Details 8 5. Operating and Safety Instructions 12

6. Block Description 24 7. Theory of Operation 25

8. Detailed Circuit Description 27

9. Calibration Procedure 33

10. Adjustment Steps 34 11. Service Instructions 41

12. Part List 45 13. Glossary of Oscilloscope Terms 58

14. Circuit Diagrams 60 15. Fault Simulation & Step by Step Fault Finding Procedure 65

16. Procedure of Fault Finding for simulated Faults 66 17. Actual Shorting Shunt Position On Jumpers 78

18. Warranty 79 19. List of Accessories 79

ST2001E


RoHS Compliance

Scientech Products are RoHS Complied. RoHS Directive concerns with the restrictive use of Hazardous substances (Pb, Cd, Cr, Hg, Br compounds) in electric and electronic equipments. Scientech products are “Lead Free” and “Environment Friendly”. It is mandatory that service engineers use lead free solder wire and use the soldering irons upto (25 W) that reach a temperature of 450°C at the tip as the melting temperature of the unleaded solder is higher than the leaded solder.

Introduction Even though a large amount of developments have taken place in electronics, the Oscilloscope is still a widely used instrument for testing of analog and digital circuits. The dynamic performances of the circuits like instantaneous values, fast responses and many other parameters are easily analyzed on Oscilloscope. Full understanding of the working of Oscilloscope and operation of various controls thus has become very important in education. SCIENTECH Oscilloscope Demonstrator-cum-Trainer ST2001E specifically designed for the study of working of Oscilloscope. It is a user friendly, fully working Oscilloscope in an open form. The controls are placed actually at the places as they are in the circuit schematic. And thus trainee can look at it any sections, components of the section and can study it thoroughly. The function controls are adjustment controls, fully adjustable to the trainee and to verify their effect on the working of the scope.

A new concept has been evolved, fault simulation, to train on actual fault-finding, by simulating faults in the instruments. The faults created in the instrument no way affects or damage the instrument. The Instructor can introduce faults of his/her choice from the standard 15 faults and ask trainee/student to probe into it and to find out the cause of the fault. This way trainee gets complete insight of training of faults in the electronic circuits.

An illustrated block and circuit schematic and the adjustment plan right in front of trainee's eye helps him/her to correlate each operation during the demonstration.

We hope our attempt will help the user to understand the working of the Oscilloscope and shall further help to achieve the best from any Oscilloscope used by them.

ST2001E


Technical Specifications Operating Modes : CH 1, CH 2, CH 1&11 Alt / Chopped, (approx. 350 KHz), X-Y operation: 1:1

Vertical Deflection : (Both Channels)

Bandwidth : DC 20 MHz (-3dB) Rise time: 17.5 ns (approximately) Deflection Coefficients :12 steps 5mV/cm - 20V/cm (1-2-5 sequence) Accuracy : ± 3% Input Impedance : 1MΩ || 30pF Input coupling : DC-AC Gnd Max. input : 350V (DC+ peak AC)

Time Base :

Time coefficients : 18 steps, 0.5µs/ cm0.2s/ cm(1-2-5 sequence) with Mag X5 to 100 ns/cm. with variable to 40 ns/cm Accuracy : ±3 % (In cal position) Sweep Output : Approximately 5V (peak to peak)

Trigger System : Modes : Auto or variable Source : CH 1 or CH 2, external Slope : Positive or Negative Coupling : AC, TV frame Sensitivity : Internal 0.5cm External 0.8V Trigger Bandwidth : 40 MHz

Horizontal Deflection : Bandwidth : DC- 2 MHz (-3dB) XY mode : Phase shift < 5° 60 KHz Deflection coefficients : 12 calibrated steps 5 mV /cm-20V /cm Input Impedance: 1M Ω || 30 pF

Component Tester : Test Voltage : Max. 8.6 Vrms Test Current : Max. 8 mArms Test Frequency : 50 HZ Test circuit ground to chassis

Miscellaneous : Fault Simulation : Total of 15 faults can be simulated. Detailed Trouble shooting Procedure included. Cathode ray tube : 140 mm Rectangular Tube with internal graticule,(P-31) phosphor Accelerating potential : 2000 VDC Display : 8x10 cm Trace rotation : Adjustable Calibrator : Square wave 1KHz (approx.) 0.2V +1% Z Modulation : TTL level Mains Voltage : 230V ±10% 50Hz Power Consumption : 36 VA (approximately) Weight : 7.3 Kg (Approximately) Dimensions (mm) : W450 x H145 x D420

Subject to change

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Front Panel Controls

(1) Power ‘On/Off’ : Turns ‘On’ & ‘Off’ (on in open cover condition

only.) LED indicates power ‘On’. Use position & Int/Focus controls to get the beam. All push buttons.

(2) Time / Div : Rotary Switch for TB speed control. (3) Trigger Input : For feeding External trigger signal. (4) Volts/Div : For sensitivity selection of CH 1 & CH 2. (5) DC-AC-Gnd : Switch provided for Input coupling. BNC inputs

provided for connecting the Input signal. (6) Component Tester : Switch when pressed converts scope into

Component Tester mode. (7) CT : Input & Gnd terminals to be used for CT.

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Controls on PCB

(1) Intensity : Controls the brightness (2) Focus : Controls the sharpness (3) Trace Rotation : Controls the horizontal alignment of the trace. (4) X Pos : Controls the horizontal position (5) Y Pos I & II : Controls vertical position of the trace. (6) X Y : When pressed cuts-off internal TB & connects

external horizontal signal via. CH II (7) X 5 : When pressed gives 5 times magnification. (8) External : When pressed allows ext. trigger. (9) TV : When pressed allows TV frame to be

synchronized. (10) Cal Variable : Controls the time speed in between the steps. (11) Auto/ Norm : In AT gives display of trace & auto trigger.

When pressed becomes normal & gives variable level trigger.

(12) Level : Controls the trigger level from positive peak to negative peak.

(13) + / - : Selects the slope of triggering. (14) Trig 1/ Trig 2 : When out trigger CH I and when pressed

triggers CH II (15) CH I Alt/ : When out selects CH I and when pressed selects CH II Chop CH II. When dual switch also pressed this

selects Alt or Chop modes. (16) Mono / Dual : When out, selects CH I only. When pressed

selects both.

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Test Point Details Signal waveforms on test points are taken by feeding sine wave signal (1Vpp at 5 KHz) to CH I and CH II, keeping CRT display 5 divisions at 0.2 V sensitivity and Input coupling to AC.

Note : 1. Blue and Red colour test points are input and output test points of that particular

section respectively. 2. The numeric value shown below in table, are only for guidelines, and actual

exact , values will depend on the calibration done.

No. Test Point No. Location Signal Contents on TP & Waveform

1. TP01 Y-Pre Amp CH I 18mVpp (approx.) (Please check on junction of D101 and gate of T101)

2. TP02 Red Y-Pre Amp CH I 380mVpp (approx.)

3. TP03 Red Y-Pre Amp CH I 380mVpp (approx.)

4. TP04 Y-Pre Amp CH II 18mVpp (approx.) (Please check on junction of D 101 & gate of T101)

5. TP05 Red Y -Pre Amp CH II 380mVpp (approx.)

6. TP06 Red Y -Pre Amp CH II 380mVpp (approx.)

7. TP07 Red Component Tester CH I Mode 5V pp CT Mode 6-22 V, According to TB position 8. TP08 Blue -do- CH I Mode 5 V

CT Mode 2.6 V

9. TP09 Red -do- - 8 V DC (approx) 10. TP10 Red -do- CH I Mode + 1.8 V

CT Mode 0.8V

11. TP11 Blue -do- 22Vpp (approx)

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12. TP12 Red Chopper Circuit at CH I mode + 13 V DC

CH II mode +8 V DC

Dual + A1t mode 13. TP13 Red - do - at CH I mode +8 V DC CH II mode +13 V DC

Dual 1+ Alt mode

Dual + Chop mode

14. TP14 Red Trigger Amp. circuit CH II mode 6 Vpp

XY mode 2.2 Vpp

15. TP15 Red - do - Trigger signal 3V pp

in XY mode 4Vpp

16. TP16 Blue - do - Trig 1 mode 24 V Trig 2 mode OV

17. TP17Blue - do - Trig 1 mode 0 V Trig 2 mode 24 V

18. TP18 Blue Y intermediate Amp 380mVpp

19. TP19 Blue - do- 380mVpp

20. TP20 Blue - do- 380m V pp

21. TP21 Blue - do- 380mVpp 22. TP22 Blue - do- same as TP13

23. TP23 Blue - do- same as TP12

24. TP24 Red - do- 140 mV (approx.)

25. TP25 Red - do- 140 mV (approx.)

26. TP26 Red Ext. X XY mode 2.5 V pp

27. TP27 Red Trigger Circuit Ext. trigger signal 28. TP28 Blue - do - at negative mode 2.2 V pp

29. TP29 Blue - do- at positive mode 2.2 V pp

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30. TP30 Red -do - 3.5 V pp

31. TP31 Red Time base circuit 3.5 V pp

32. TP32 Blue -do - 4V

33. TP33 Red -do -- 4.8 - 5.2Vpp

34. TP34 Red -do -- 4.8 - 5.2Vpp

35. TP35 Blue X Final Amp CH I mode + 2 V 36. TP37 Blue -do - 0 - 9V DC variation by X-Pos

37. TP38 Red -do - 100 V pp

38. TP39 Red -do - 100 V pp

39. TP40 Blue Calibrator circuit 0.2 V pp

40. TP41 Blue Y Final Amp. Low Voltage

41. TP42 Blue - do - Low Voltage

42. TP43 Red -do - 30 V pp

43. TP44 Red -do - 30 V pp 44. TP45 Red Geometry + DC V adjustable

45. TP46 Red Astig + DC V adjustable 46. TP47 Blue Power Supply 153 V AC (approx)

47. TP 48 48. TP49 Blue -do - 169 V AC (approx.)

49. TP50 Blue 50. TP5l Red -do - 265 V DC (approx.)

51. TP52 Red -do - + 145 V DC (approx.) 52. TP53 Blue

53. TP54 Blue -do - 16 V AC (approx.) 54. TP55 Red -do - - 12 V DC

55. TP56 Blue 56. TP57 Blue -do - 9 V AC (approx.)

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Sr. No. Test Point No. Location Signal Contents on TP & Waveform 57. TP58 Red -do - + 5 V DC

58. TP59 Blue 59. TP60 Blue -do - 26 V AC (approx.)

60. TP61 Red -do - +24 V DC

61. TP62 Blue

62. TP63 Blue -do - 8 V AC (approx.) 63. TP64 Blue -do - 35 V AC w.r.t. -1900V (approx.) Caution! High voltage 64. TP65 Blue - do- 6.3 VAC w.r.t.-1900 V (approx.) Caution! High voltage 65. TP66 Blue - do - 530 V AC (approx.) Caution! High voltage 66. TP67 Blue 67. TP68 Blue - do- Z modulation input (2mm Black sockets)

68. TP69 Red - do- -1900 V DC Caution! High voltage 69. TP70 Red - do- -2000 V DC Caution! High voltage 70. TP71 Red - do- Unblanking input IC CNY 17 71. TP72 Red - do- + 12 V DC

72. TP73 Red - do- + 12 V DC

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Operating and Safety Instructions General Information : The Oscilloscope - cum - Demonstrator is easy to operate. The logical arrangement of the controls allows anyone get familiar with the operation of the instrument in a short time. However, even experienced users are also advised to read through these instructions so that all functions are understood. Immediately after unpacking, the instrument should be checked for mechanical damage and loose parts in the interior. If there is transport damage, it must be informed immediately. The instrument must then not be put into operation.

Safety : The case, chassis and all measuring terminals are connected to the protected earth contact of the inlet. The mains plug shall only be inserted in a socket outlet provided with a protective earth contact. The protective action must not be negated by the use of an extension cord without a protective conductor.

Warning ! Any interruption of the protective conductor inside or outside the instrument or disconnection of the protective earth terminal is likely to make the instrument dangerous. Intentional interruption of the protective earth connection is prohibited. The mains/line plug should be inserted before connections are made to measuring circuits. Under certain condition, 50 Hz hum voltage can occur in the measuring circuit due to interconnection with other mains/line powered equipment or instrument. This can be avoided by using an isolation transformer between the main/line outlet and power plug of the instrument. When displaying waveforms where the low level side of the signal is at high potential, even with the use of a protective isolation transformer, it should be noted that this potential is connected to the Oscilloscope's case and other accessible metal parts. High voltages are dangerous. In this case, special safety precautions are to be taken. Whenever it is likely that protection has been impaired, the instrument shall be made imperative and be secured against any unintended operation. The protection is likely to be impaired if, for example, the instrument.

• Shows visible damage.

• Fails to perform the intended measurements,

• Has been subjected to prolonged storage under unfavorable conditions (e.g. in the open or in moist environments).

• Has been subjected to severe transport stress (e.g. in poor packaging).

Operating Conditions : The instrument has been designed for indoor use. The permissible ambient temperature range during operation is 10°C-40°C. The permissible ambient temperature range for storage or transportation is -20°C to +70°C. The maximum operating altitude is upto 2200 (non-operating 15000 m). The maximum relative

ST2001E


humidity is up to 90 %. If condensed water exists in the instrument it should be acclimatized before switching on. In some cases (e.g. extremely cold Oscilloscope) two hours should be allowed before the instrument is put into operation The instrument should be kept in a clean and dry room and must not be operated in explosive, corrosive, dusty, or moist environments.

First Time Operation : Check that the instrument is set to the correct mains/line voltage. Before applying power to the Oscilloscope it is recommended that the following simple procedures are performed

• Both DC-AC Gnd input coupling slide switches for CH I and CH II in the Y -field should be set to Gnd position. Open the lid of the scope.

• Check that all push buttons are in the out position, i.e. released.

• Rotate the i.e. Time/Div. variable control, fully counter-clockwise to a position.

• Set all controls with marker lines to their mid range position. Switch on the Oscilloscope by pressing the red Power push-button. An LED will illuminate to indicate working order. The trace displaying one base line should be visible after a short warm up period of 10 seconds. Adjust Y Pos. I and X Pos. controls to center the baseline. Adjust Intensity and Focus control for medium brightness and optimum sharpness of the trace. The Oscilloscope is now ready for use. If only a spot appears (Caution! CRT phosphor can be damaged), reduce the intensity immediately and check that the X-Y push button is in the released (out) position. If the trace is not visible check the correct positions of all knobs and switches (particularly Auto/Norm. button in released position).

To obtain the maximum life from the cathode-ray tube, the minimum intensity setting necessary for the measurement in hand and the ambient light conditions should be used. Particular care is required when a single spot is displayed, as a very high intensity setting may cause damage to the fluorescent screen of the CRT. Switching the Oscilloscope off and on at short intervals stresses the cathode of CRT and should therefore be avoided. The instrument is so designed that even the incorrect operation will not cause serious damage. The push-buttons control only minor functions, and it is recommended that before commencement of operation all push buttons are in the "out" position. After this the push buttons can be operated depending upon the mode of released required. All knob and switches should again be checked to ensure that the correct positions have been selected. Moreover, particular attention should be paid to the 'Level' control. In the absence of an input signal the baseline will only be displayed if this control is in the fully anti clockwise and locked position 'Auto' (Automatic triggering). If only a dot appears (Caution! The CRT phosphor could be damaged under this condition) probably the push button for XY is pressed. If this is so, it should be released. Now, the base line should appear and the 'Intensity' control should be adjusted for average brightness, while optimum sharpness is obtained by adjusting the 'Focus' control. At the same time both input coupling switches 'DC-AC Gnd

ST2001E


should be in the 'Gnd' position. Thus, the inputs of the Y-amplifiers are shorted preventing the introduction of unwanted signals.

Trace Rotation (TR) : In spite of Mu metal-shielding of the CRT, effects of the earth's magnetic field on the horizontal trace position cannot be completely avoided. This is dependent upon the orientation of the Oscilloscope on the place of work. A centered trace may not align exactly with the horizontal centre line of the graticule. A few degree of misalignment can be corrected by a potentiometer in the trace rotation section.

Type of the Signal Voltage : All types of signals whose frequency spectrum is below 20 MHz can be displayed on the ST2001E. The display of simple electrical processes such as sinusoidal RF and AF signal or 50Hz ripple voltages poses no problems. However, when square or pulse shaped signals are displayed it must be remembered that their harmonic content must also be transmitted. The bandwidth of the vertical amplifier must therefore, be considerably higher than the repetition frequency of the signal. Greater problems occur when composite signals are to be displayed, especially if they do not contain any suitable level components at the repetition frequency which can be used for triggering. To obtain a well triggered display in this case, it may be necessary to use the time base 'Var' control. Television video signals are relatively easy to trigger. However, when investigating signals at Name frequency, the 'TV' pushbutton must be in this way, the more rapid line pulses can be attenuated so that, with appropriate level adjustment, triggering can easily be carried out on the leading or trailing edge of the frame synchronizing pulse. For optional operation as an AC or DC voltage amplifier, each channel is provided with an 'AC-DC' switch. The DC range should only be used if the acquisition of the DC voltage content of the signal is absolutely necessary. However, when investigating very low frequency pulses, disturbing ramp offset may occur with AC coupling. In this case DC coupling must be used. DC voltages are always measured in the 'DC' position. DC operation is to be recommended even for the representation of logic and pulse signals, particularly if the duty cycle permanently changes during operation. Otherwise, the display will move up and down with any change.

Amplitude Measurements : In general electrical engineering, alternating voltage data normally refers to effective values (rms = root-mean-square value). However, for signal magnitudes and voltage designations in Oscilloscope measurements, the peak-to-peak voltage (Vpp) value is applied. The latter corresponds to the real potential difference between the most positive and most negative points of a signal waveform. If a sinusoidal waveform, displayed on the Oscilloscope screen, is to be converted into an effective (rms) value, the resulting peak-to-peak value must be divided by 2 x √2 = 2.83. Conversely, it should be observed that sinusoidal voltages indicated in Vrms (Veff) have 2.83 times the potential. Different voltage magnitudes can be seen from the following figure 1.

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Figure 1

Vrms = effective value Vp = simple peak or crest value Vpp = peak-to-peak value Vmom = momentary value. The maximum signal voltage required at the vertical amplifier input for a display of 1 cm is approximately 5mVpp. This is achieved with the attenuator control set at 5mV/cm, however smaller signals than this may also be displayed. The deflection coefficients on the input attenuators are indicated in mV/cm or V/cm (peak-to-peak value).

The magnitude of the applied voltage is ascertained by multiplying the selected deflection coefficient by the vertical display height in cm. If an attenuator probe X10 is used, a further multiplication by a factor of 10 is required to ascertain the correct voltage value.

With direct connection to the vertical input, signals upto 160 Vpp may be displayed. With the designations:

H = display height in cm U = signal voltage in Vpp at the vertical input. D = deflection coefficient in V/cm at attenuator switch, The required quantity can be calculated from the two given quantities:

U=D.H. H=U/D D=U/H However, these three values are not freely selectable. They have to be within the following limits (trigger threshold, accuracy of reading). H between 0.5 and 8 cm. if possible 3.2 to 8 cm. U between 2.5 mVpp and 160 Vpp, D between 5mV/cm and 20V/cm in 1-2-5 sequence.

Examples : Set deflection coefficient D = 50 mV /cm = 0.05 V /cm, Observed display height H = 4.6 cm. Required voltage U = 0.05 x 4.6 = 0.23 Vpp Input voltage U = 5 Vpp Set deflection coefficient D = 1 V /cm Required display height H = 5/1 = 5 cm

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If the applied signal is superimposed on a DC (direct voltage) level the total value (DC + peak value of the alternating voltage) of the signal across the Y-input must not exceed + 350 V.

Reference Line : With Y-Pos control (input coupling to Gnd) it is possible to see a horizontal graticule line as reference line for ground potential before the measurement. It can lie below or above the horizontal central line according to whether positive and/or negative deviations from the ground potential are to be measured. Certain switchable X10 / X1 attenuator probes also have a built-in-ground reference switch position.

Time Measurements : As a rule, most signals to be displayed are periodically repeating processes, also called periods. The number of periods per second is the repetition frequency Depending on the time base setting of the Time/Div. switch, one or several signal periods or only a part of a period can be displayed. The time coefficients are stated in s/cm, ms/cm and µs/cm on three fields. There are 18 time coefficient ranges of the ST2001E, from 0.5s/cm to 0.2s/cm.

The duration of a signal period or a part of it is determined by multiplying the relevant time (horizontal distance in cm) by the time coefficient set on the Time/Div. switch. The variable time control (identified with an arrow knob cap) must be in its calibrated position Cal. (arrow pointing horizontally to the left).

With the designations L = displayed wave length in cm of one period. T = time in seconds for one period F = recurrence frequency in Hz of the signals, Tc = time coefficient in s/cm on time base switch and the relation

F = 1/T,

The following equations can be stated: T = Tc x L, L = T/Tc Tc = T/L

F = 1/L.Tc L = 1/F.Tc Tc = 1/L.F. With pressed X-MAG. X5 pushbutton the Tc value must be divided by 5. However, these four values are not freely selectable. They have to be within the following limits:

L between 0.2 and 10 cm, if possible 4 to 10 cm, T between 0.05s and 2s,

F between 0.5 Hz and 20 MHz,

Tc between 0.5 s/cm and 0.2 s/cm in 1-2-5 sequence (with XMAG X5 in out position)

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Examples : 1. Displayed wavelength L = 7 cm,

Set time coefficient Tc = 0.5µs/cm.

Required period T = 7 x 0.5 x 10-6 = 3.5µs Required Freq. F = 1: (3.5 x 10-6) = 286 KHz

2. Displayed ripple wavelength L = 1 cm, Set time coefficient Tc = 10 ms/cm,

Required ripple freq. F = 1: (1 x 10 x 10-3) = 100 Hz. 3. TV-line frequency F = 15,625 Hz

Set time coefficient Tc = 10µs/cm Required wavelength L = 1: (15625 x 10-5) = 6.4 cm. 4. Sine wavelength L = min. 4 cm, max. 10 cm,

Frequency F = 1 KHz. Max. Time coefficient Tc = 1: (4 x 103) = 0.25 ms/cm,

Min. Time coefficient Tc = 1: (10x 103) = 0.1 ms/cm. Set Time coefficient T = 0.2 ms/cm,

Required wavelength L = 1: (10 x 0.2 x 10-3) = 5 cm. 5. Displayed wavelength L = 0.8 cm.

Set time coefficient T = 0.5 µs/cm.

Pressed X-Mag X5 button: T = 0.1µs/cm, Required. Frequency F = 1: (0.8 x 0.1 x 10-6) = 12.5 MHz

Required period t = 1: (12.5 x 106) = 80 ns. If the time is relatively short as compared to the complete signal period, an expanded time scale should always be applied (X-Mag X5 button pressed). In this case, the ascertained time values have to be divided by 5. The time interval of interest can be shifted to the screen center using the X-Pos. control. When investigating pulse of square waveforms, the critical feature is the rise time of the voltage step. To ensure that transients, ramp offset, and bandwidth limits do not unduly influence the measuring accuracy, the rise time is generally measured between 10% and 90% of the vertical pulse height. For peak-to-peak signal amplitude of 5 cm height, which are symmetrically adjusted to the horizontal center line, the internal graticule of the CRT has two horizontal dotted lines ± 2.5 cm from the center line. Adjust the Y attenuator switch together with the Y Pos. Control so that the pulse height is precisely aligned with these 0 and 100% lines. The 10% and 90% points of the signal will now coincide with the two lines, which have a distance of ± 2 cm from the horizontal center line and an additional subdivision of 0.2 cm. The rise time is

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given by the product of the horizontal distance in cm between these two coincidence points and the time coefficient setting. If magnification is used, this product must be divided by 5. The fall time of a pulse can also be measured by using this method.

With a time coefficient of 0.5µs/cm and pushed X-Mag X5 button the example shown in the figure No.2 results in a measured total rise time of

Ttot = 1.6 cm x 0.5µs/cm : 5 = 160ns

Figure 2

When very fast rise time is being measured, the rise time of the Oscilloscope amplifier and of the attenuator probe has to be deducted from the measured time value. The measurement applies.

tr = 350 / B or B = 350 / tr

Connection of the Test Signal : Caution ! When connecting unknown signals to the Oscilloscope input, always use automatic Triggering and set the DC-AC input coupling switch to AC. The attenuator switch should initially be set to 20 V/cm. The signal to be displayed should be fed to the Y input of the Oscilloscope by means of a shielded test cable or by an X10 attenuator probe. The use of these cables with high impedance circuits is only recommended for relatively low frequencies (upto approximately 50 KHz). For higher frequencies and when the signal source is of low impedance, a cable of matched characteristic impedance (usually 50 Ω) is recommended. When investigating square or pulse waveforms with fast rise time, transient phenomenon on both the edges and top of the signal may become visible, if the correct termination is not used. It must be remembered that the 50 Ω through- termination will dissipate a maximum of 2 watts. If an X10 attenuator probe is used, no termination is necessary. In this case, the connecting cable is matched directly to the high impedance input of the Oscilloscope. With attenuator probe, even high-internal impedance sources are only slightly loaded. Therefore, when the voltage loss due to the attenuation of the probe can be compensated by a higher sensitivity setting on the ST2001E, the probe should always be used.

Additionally, it provides the series protection for the input of the Oscilloscope amplifier. Note that all attenuator probes must be compensated in conjunction with the Oscilloscope.

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It is important to remember that for the display of small signal voltages the position of the ground point on the test circuit can be critical. It should always be located as close as possible to the measuring point. If this is not done serious signal deformation may result from any invalidated currents through ground leads or chassis parts. This also applies to the ground leads of the attenuator probes. These should ideally be as short and thick as possible. If after connecting the test signal, the trace disappears suddenly, the signal amplitude may well be too large, i.e. the amplifier is over scanned. In this case, the attenuator switch should be turned anti-clockwise, until the vertical deflection is only 3-7 cm. For signal amplitudes greater than 160Vpp a X10 probe should always be used. If after connecting the signal the intensity of the trace is low, it is possible that the period of the test signal is substantially slower than the value set of the 'Timebase' switch. This control should then be turned anti-clockwise to a corresponding slower time coefficient.

Probe Compensation : For the undistorted display of signals, the X10 attenuator probe must be compensated to match the input impedance of the vertical amplifier. This can be easily achieved as ST2001E has a built-in Square Wave Generator with a repetition frequency of approximately 1 KHz and an output voltage of 0.2Vpp. The method employed is as follows : The probe tips are connected to the test-point TP40 marked with a cal Out, and adjusted by using the trimmer tool supplied with the probe. The correct display is shown in figure 3.

Figure 3

The 'Timebase' switch should be in the '0.2 ms/cm' position. The signal has amplitude of 0.2Vpp ± 1 %. If the attenuator switch is set to 50 m V /cm, the display will have a height of 4cms (1:1 probe). Since an attenuator probe is constantly subjected to considerable stresses, the compensation should be frequently checked.

Operating Modes : The required operating modes are selected with push buttons in the vertical amplifier section. For 'Mono' operation with channel I only, all push buttons should be out. For 'Mono' operation with channel 2, only, the 'Alt/Chop' button must be pressed. For internal triggering with the signal from channel 2, the Trig 1/2 button has to be pressed in addition. On pressing the button marked 'Mono/Dual', dual trace operation is selected. In this condition both traces are displayed consecutively (alternate sweep). This mode is not suitable for the display of very low frequency signals as the display

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will flicker or appear to jump. This can be overcome by pressing the 'Alt/Chop' button. Both channels then share the trace during each sweep period (chopped mode). For display with a higher repetition rate, the type of channel switching is less important but the alternate mode is normally suggested.

For XY operation the XY button must be pressed. The X signal is connected via the input of channel 2. The sensitivity of the horizontal amplifier during X-Y operation is selected by the CH II attenuator switch. The sensitivity and input impedance for both the X & Y axes are equal. Note that the frequency limit of the X axis is approximately 2 MHz (-3 dB). Therefore, an increase in phase difference is noticeable at higher frequencies. The phase shift is 3° approximately at 60 KHz. Lissajous figures can be displayed in the X- Y mode for certain measuring tasks.

• Comparing two signals of different frequency or bringing one frequency upto the frequency of the other signal. This also applies for whole number multiples or fractions of the one signal frequency.

• Phase comparison between two signals of the same frequency.

Phase Comparison with Lissajous figure : The figure 4 shows two sine signals of the same frequency and amplitude with different phase angles.

Calculation of the phase angle or the phase shift between the X and Y input voltages (after measuring the distances a and b on the screen) is quite simple with the following formula and a pocket calculator with trigonometric functions and besides independent of both deflecting amplitudes on the screen.

Sin θ = a/b

2

ba1θ Cos

−=

ba1-Sin =θ

Figure 4

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The following must be noted here :

• Because of the periodic nature of the trigonometric functions, the calculation should be limited to angles 90°. However here is the advantage of the method.

• Do not use a too high test frequency. The phase shift of the two Oscilloscope amplifiers of the ST2001E in the X-Y mode can exceed an angle 3° above 100 KHz.

• It cannot be seen as a matter of course from the screen display if the test voltage leads or lags the reference voltage. ACR network before the test voltage input of the Oscilloscope can help here. The 1MΩ Input resistance can equally serves as R here, so that only a suitable capacitor C needs to be connected in series. If the aperture width of the ellipse is increased (compared with C short-circuited), then the test voltage leads the reference voltage and vice versa. This applies only in the region up to 90° phase shift therefore C should be sufficiently large and produce only a relatively small just observable phase shift.

Should both input voltage be missing or fall in the X-Y mode, a very bright light dot is displayed on the screen. This dot can burn into the phosphor at a too high brightness setting (Intensity. knob) which causes either a lasting loss of brightness, or in the extreme case, complete destruction of the phosphor at this point. Trigger And Time Base : Time base operation is particularly important in obtaining a satisfactory stable display. If the 'Auto' pushbutton is not pressed the sweep generator will be triggered automatically. The time axis (baseline) is then also visible without applying a signal voltage. In this position practically all uncomplicated, periodically recurring signals above 30 Hz repetition frequency can be displayed in a stable locked in position. Operation of the time base is then restricted mainly to adjusting the time setting.

To obtain a stable display at all frequencies the time base must be triggered synchronously with the applied signal. Triggering can be initiated by this signal itself or by a different externally fed-in voltage, which must also be in synchronism. For this purpose, press the 'External.’ button. The trigger signal (at least 1Vpp) is applied to the socket marked 'Trigger Input. On single channel operation a trigger signal may also be applied to the input of channel 2 (in this case trigger selector button ' Trig 1/2' must be pressed). This method is recommended if the amplitude of the trigger signal does not fall in the range 1 to 6Vpp, or if it is unknown value. Using this method the signal can be adapted to the trigger input of the time base within a range of 5mVpp to approximately 160Vpp by means of the CH II attenuator switch. Initially the unknown external trigger signal should be displayed and then adjusted to a peak-to- peak amplitude of 3-6 cm. The trigger signal can be taken either from CH I or 2. Selection is made by means of the button marked ' Trig 1/2 in trigger Amp circuit. If possible, it is always better to trigger with the less complicated signal. To select the trigger edge, use the '+/-'button. When it is not pressed, all displays start with a positive-going rise.

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As already described, simple signals may be triggered automatically, i.e. without pressing 'Auto/Norm' switch. However, if the pulse duty factor of a square signal changes drastically, and a part of this square-wave deforms to a needle pulse, the operation of the 'Level' control may become necessary, after pressing ''Auto/Norm'' switch. With composite signals the trigger facility is dependent on the occurrence of certain periodically recurring levels. The 'Level' adjustment of these signals will require care. If, for example, the complex video signal of a television set is to be displayed at frame frequency, synchronization is generally difficult due to the faster sequence of the line pulses contained in the signal. For attenuation of the line pulse, the 'TV' button must be pressed. This setting is also advantageous for triggering other signals below a repetition frequency of 1KHz as high frequency harmonics or noise in the trigger signal are suppressed by the presence of the low pass filter.

If no triggering point can be found on complex signals even after repeated and careful adjustment of the 'Level' control it may be possible to obtain one by adjusting the 'Var' control. Sometimes it can also be advantageous to use only the 'Var' control.

All coefficient settings on the "Timebase" switch are calibrated when the 'Var' control is set at the 'Cal' position. With 'Var' control in the anti-clockwise position the sweep rate is made faster by a factor of 2.5. This factor is not precisely calibrated. With the X5 expansion of the sweep a maximum sweep of approximately 40 ns/cm is obtained. The choice of the optimum time coefficient depends on the repetition rate of the signal being measured.

Component Tester : General : Oscilloscope demonstrator ST2001E comes with an additional facility, a built-in Component Tester. This allows passive and active components like resistors, capacitors, inductors transformer, silicon/germanium diodes, zener, tunnel diode, Schottky diodes, transistors, JFETs, MOSFETs, UJTs, SCRs, TRIACs, and even linear and digital ICs to be tested while still in circuit. Using the ST2001E Component Tester is very simple. Just push in the CT switch, plug in two test sockets marked CT-Input. A horizontal line about 5 to 6 cms will be seen. On shorting the two test prod tips a vertical line is seen. Connect the component under test across the prods. Some typical test patterns are shown on the following page figure 5.

Only remember to keep the scope in the CH I operating mode and Ground the input of CH I. After use, to return the Oscilloscope to normal operation, release the CT push button.

Caution ! Do not test any component in live circuit; remove all grounds, power and signals connected to the component under test leads across component to be tested. Observe Oscilloscope display.

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Test Pattern Displays : 1. The figure shows typical test patterns displayed by the various components

under test. It may be noted here that component testing is a two terminal check across any two points to find out what has happened across that. It may show a healthy PN or NP junction. It is a qualitative test and does not indicate any quality.

2. Open circuit is indicated by a straight horizontal line. 3. Short circuit is shown by a straight vertical line.

4. A horizontal ellipse indicates high impedance or a relatively small capacitance or a relatively high inductance.

5. A vertical ellipse indicates small impedance or a relatively large capacitance or a relatively small inductance.

6. A tilted ellipse means that the component has a considerable ohmic resistance in addition to its reactance.

Figure 5

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In-Circuit Tests : Caution ! During in-circuit tests make sure the circuit is dead. No power from mains/line or battery and no signal inputs are permitted. Remove all ground connections inclusive safety earth (pull out power plug from outlet). Remove all measuring cables inclusive probes between Oscilloscope and circuit under test.

Block Description In this section of manual, we will be studying the block diagram of a basic 20 MHz, dual channel Oscilloscope demonstrator followed by detailed description of each major circuit.

On the next page a block diagram is illustrated from the block diagram, we find that the Oscilloscope consists of the following basic circuits,

1. Y input for CH 1 & CH 2 2. Input attenuator for CH 1 & CH 2

3. EY / ATT preamplifier CH 1 & CH 2

4. Y Intermediate amplifier for CH 1 & CH 2

5. Y Final amplifier 6. Channel selector and chopper generator

7. Trigger Amplifier 8. Trigger amplifier & comparator

9. Time Base Circuit 10. X Final Amplifier

11. EHT & Unblanking circuit 12. Component Tester

13. Calibrator Output 14. Power Supply

15. Trace Rotation circuit The connection of these circuits is as shown in the block diagram figure no. 6.

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Block Diagram of ST2001E

Figure 6

Theory of Operation General Description : The basic objective of an Oscilloscope is to read an unknown signal & display it on the screen for observation and measurements. These signals are applied on the input of either channel or simultaneously on both channel inputs. The input attenuator then attenuates the signal with appropriate attenuation and displays on the screen. The selection of input may be AC component of DC + AC components. The disconnection of signal from source is to be done with input switch to Gnd position.

The output signal of attenuator is then applied to preamplifier stage, where a high input, high gain bandwidth FET input is applied. Here, signal is isolated from input, applied to preamplifier for further amplification and converting the input to two line outputs.

In Y intermediate amplifier, two channels are selected, either CH I or Chin or both in alternate or chop mode. This is done with the help of diodes switching amplifier.

The selected output form Y intermediate amplifier is applied for Y final amplifier. This circuit amplifies sufficient output signal level necessary to drive the Y plates of CRT, for appropriate deflection of electron beam. The Y amplifier is designed in such a way so that it gives good extended Guassian roll-off with minimum noise level.

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The time base circuits adjust the sweep / ramp signal so that Y input signal can be resolved in time direction / X direction for measurement of waveform or a portion of waveform. This is a calibrated ramp and hence time measurements are made with the help of this circuit.

The signal applied is to be synchronized with sweep output. This is known as triggering of signal. In auto mode as and when signal is applied to the input of scope, it gets triggered/synchronized with ramp at almost at zero crossing of signal. Whenever, a trigger level is to be adjusted, a level control is used to set the desired trigger level. While triggering, one can select the different available coupling like AC, DC internal, external, CH I or CH II.

AC trigger is used over a wide range of signals from 10 Hz to 20 MHz. While triggering, low frequency signals like few Hertz, the trigger point may shift. For stable DC trigger coupling is used. It works from DC to 20 MHz signals. A TV sync circuit is provided for stable triggering on television vertical sync pulses. This can select H and V frame as required.

The ramp output , synchronized with input signal is given at preamplifier input, where X position on the screen is given at preamplifier input, where X position on screen can be adjusted as X-Pos and in the circuit X1-X5 magnification is provided.

The preamplifier output is then applied to X final amplifier for appropriate magnification, to be applied to X plates of the CRT.

In the X-Y mode of operation, the X input signal is applied on CH II and Y input signal to CH I. The X signal applied on CH II is passes through attenuator preamplifier, CH II trigger selector, trigger amplifier and then to X plate via X final amplifier.

In the CRT circuit, a negative potential is applied at Cathode to accelerate the electron beam. The astigmatism, an unblanking circuit along with Z modulation, intensity, focus control etc. are been arranged in the circuit. The power supply circuit provides the necessary operating voltages for the instrument. The operating potentials are obtained from the voltage regulator circuit and HV power supplies.

In calibrator circuit, a probe compensation output is provided for compensating X10, X100 and other attenuator or probes, to adjust with input capacitance of Oscilloscope input. The potential is 0.2 V square waves 1 KHz approximately.

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Detailed Circuit Description Note : Please refer to the circuit diagram given at the back of the manual when reading the circuit description.

Vertical Attenuators : The input signal once passed through input coupling (identical for each channel) is appearing at wafer of attenuator rotary switch. Here input is divided in 1:1 or 10:1 or 1000:1, depending upon the switch position. The pre-attenuated signal is again attenuated to 1:1 or 2:1 or 4:1 depending upon attenuation position for required sensitivity.

These attenuators are designed in such a way that the input signals see constant 1M Ω25pF impedance. While in testing this circuit has a minor adjustment of capacitance of different arms of attenuator circuit. The attenuation capacitance is adjusted for exact division of signal. (Discussed the same in the, calibration procedure).

Since this attenuator circuit is quite sensitive to noise, that's why; this is packed in shield made of tin sheet. The CH II attenuator is exactly identical to CH I.

Y Attenuator Preamplifier : The attenuated signal is applied at input gate of, matched, made on the same substrate FET. The output of this is applied at pin no. 14 of IC NE592, video amplifier. At pin no.1 the DC balance voltage is applied, so that output (dual) at pin no. 7 and 8 have equal DC voltages.

The gain of IC is adjusted with the help of the resistor R122 such that the output of pin no. 7 and 8 will be 45mV/Div on the screen.

Y Intermediate Amplifier : There are two identical intermediate amplifiers are used, as shown below. In each amplifier, matched transistors are used. The gain adjustment is done with the help of VR 203, VR 204 for CH I, Chin in their respective amplifier. This also set the final gain of Y amplifier. (See adjustment procedure).

Channel Selection, Dual Alternate and Chopped : Channel I Selection : The CH I is selected when CH I / CH II, Trig 1 / Trig 2 switch is out position. In this case the potential is applied on S/R input of D flip-flop IC 4013. This gives Q output at 13 to low, so that transistor T251 doesn't 'On' and hence diode D202 and D203 are reverse biased, and diode D204 and D201 conducts and hence selects CH I . While Q is low Q is high and transistor T252 conducts, causes diode D206 & D207 to forward bias and thus stopping conduction through D205 and D208.

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Channel 2 Selection : In this case when CH I / CH II switch pressed, it causes Q to be high and Q to be low, and similar action will be take place, as discussed above , diode D201 and D204 doesn't conduct and D208 and D205 conducts, hence CH II is selected. Dual CH I and CH II, Alternate : When dual channel to be selected, by pressing Dual push button, irrespective of CH I / CH II position. When pressed dual switch S252, diode D251 and D252, gets -12V through switch S252 and the circuit appearing on base of T254 is transformed to D input pin no. 11 of IC 4013 flip-flop. This causes Q and Q to switch to '1' and ‘0’, i.e. toggle, and thus CH I and CH II is selected alternatively. Dual Channel Chopped : The other flip-flop in IC 4013 is used for making chopper generator. This is nothing but an astable multi-vibrator whose output is at approximately 500 KHz. When switch 8251 and 8252, dual and chop is pressed, transistor T153 gets -12V through R268 and thus chopped circuit functions. The chopper output is applied on D input of other flip-flop and CH I and CH II are now chopped while alternating the sweep. Y Final Amplifier : The pre-amplified signal emerging out of Y intermediate amplifier is fed to Y final amplifier input buffer transistor T551 and T552. The final amplifier transistors are BF 458 (selected for HFE) matched on curve tracer. This transistor converts the emitter current signal to proportional output voltages, which in turn fed to CRT plates, which deflects electron beam accordingly. The inductor L551 and L552 are provided to filter out RF signal going to power supply. The RC circuit formed by C553 + R569, R570 + C 554 and VR 552 + VC 551 does, high frequency compensation. (See adjustment procedure). Sweep Generator (Time Base or Ramp Generator) : The circuit produces a linear voltage ramp to provide horizontal deflection of CRT beam at X plates. The sweep generators also produce signals that are used to generate correct timing of CRT unblanking for viewing the signal display. The sweep logic circuitry controls the hold-off. Time (natural hold-off time), starts the sweep upon reception of trigger signal and terminates the sweep at proper voltage level, or discharges the timing capacitors. Even, with no signal connected to input, it will keep the sweep to run freely. The basics of this type of highly calibrated sweep lies with a Miller theory, which produces a linear voltage sweep that drives horizontal amplifier. It produces sweep by maintaining a constant current through a timing capacitor, to obtain a linearity increasing voltage. The time base circuit, has hold-off circuit for natural hold-off required by sweep generation, constant current source, timing capacitors; discharges circuit and sweep logic circuit. The hold-off, constant current source and timing capacitors are circuit changing component, with respect to time base switch position. These three circuits are build on

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an around the time base rotary switch. The contact wafer S405 W1 has hold-off charging capacitors, S405 W2 has constant current source resistors and S405 W3 has timing capacitors. Transistors T405 and T406, along with selected resistors from R431, R432, R436 from a constant current source. This current charges a timing capacitor depending upon time base speed setting position. The timing capacitors are C417, VC401, C418 and C419. The charging of these capacitors is a linear voltage increase. This voltage is sensed by transistor T405, and is being pre-amplified and the output is available at XY switch S351. The sweep is charged upto 5 Vpp, to discharge the capacitors, once it is reached 5Vpp, is done by sweep logic circuit. To do this, the rising sweep is sensed by transistor T403 along with associated circuit. When the sweep output reaches, T403 gives a pulse at pin 10 preset point of flip-flop IC402 Since discharging of capacitor is done through transistor namely T404, it requires, a little bit time, so that complete discharge of timing capacitor occurs. This timing is known as hold-off time and it is being generated by R429 mounted on S405 W1 wafer. This current charges one on the hold-off capacitors C414 or C415. The sensing of this charging time is conveyed to clear point of flip-flop IC 402, after desired voltage height, the hold-off voltages get discharged through transistor T404 through D405 and D420, at the same time appears on clear. When the two pulses namely-preset and clear pulse reaches to the flip-flop, changes Q and Q accordingly. This flip-flop is known as hold-off flip-flop. There is another flip-flop is used, named as sweep flip-flop IC 402a. Here, preset state is derived from At/Level function. When, in auto mode, the preset point is kept on by transistor T40 I and the clear pulse derived from Q output of hold-off flip-flop. Since pin no. 2 is tied to a high state, through +Vcc and hence if any trigger pulse available then a synchronous output Q and Q are developed on sweep flip-flop. Otherwise a free run Q and Q appears. Thus, triggering is said to be in function. The output of sweep flip-flop is given to discharge transistor T404, thus in turn discharges. This discharge pulse is hold for certain time, i.e. hold-off time of circuit. The Q output of sweep flip-flop serves two purposes; it is used for unblanking the CRT and also for dual alternate operation. X Final Amplifier : The horizontal output amplifier provides amplification of the horizontal signal to drive the horizontal CRT deflection plates. The signal coming to X-Final amplifier may be external X signal in XY mode or sweep output of time base circuit or component tester horizontal output. The input signal (sweep or else) to transistor base of T502 while the X position control is done on T501 transistor. This output is then reaches to final amplifier transistor T503, where the amplified signal is proportionally converted to deflection voltages, which drives X plates.

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Trigger Amplifier and Switching : The trigger circuit is as shown below. The trigger signal is picked up from the attenuator preamplifier circuit output. This is similar to selection of Y input signal to Y intermediate amplifier. Here for selection of trigger signal, also use a trigger intermediate amplifier. The switching of trigger 1 and 2 selects the output of this circuit. This is similar to channel selection in Y amplification.

This is achieved with the help of T317 and T320. The output is then fed to Int/Ext trigger selection switch S401. If internal triggering is chosen, the trigger preamplifier output is used for triggering; otherwise an external source can be used. The different trigger coupling can be used before the signal is fed through comparator IC401 input. The slope of the trigger can be changed to either positive or negative edge. Switch S402 selects the stable trigger of television signal.

For good triggering, a threshold of trigger input is adjustable through preset VR401, which gives 5 mm internal triggering level. The pulse train, in synchronous to signal input and whose width is adjusted accordingly for level triggering. The output of this comparator is then fed to sweep flip-flop in time base circuit for stable synchronization of time base to signals.

CRT Circuit & Unblanking : In CRT, for heating of filament in electron gun, 6.3V AC derived from mains transformer. The -1900 V EHT potential is connected to one of the filament terminal. A 100 V Zener diode is used too. This difference in potential is used for controlling the intensity of electron beam. The intensity potential is varied at G1, as required, with the help of P902. Intensity potentiometer control on EHT circuit. The upper lower cut-off potential is adjusted with the help of presets VR 901 and VR902.

The focus potential, applied on grid G3, is derived from potential adjustment of P901.

For viewing the signal, the CRT is required to be unblanked. To do so unblanking pulse is taken from sweep flip-flop pin 5, to the base of transistor T954. The output of this transistor is fed to a opto coupler IC 951, which transmits the pulses to base of transistor in opto coupler, so that isolation is come into picture between high and low potential. The output of opto coupler is fed to unblanking transistor T952, which in turn is applied to CRT cathode for unblanking. The potential of the unblanking pulse is 33V on DC-1900V. The 33 V supply is made available with zener diode D956. The transistor T95l serves as active load for unblanking transistor T952

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CRT Circuit : The high frequency unblanking pulse reaches to T952 directly from coupling capacitors C953, C954 and C955. This gives almost same response from very low time base speed to highest speed. Z modulation input (TTL level) is applied to the base of T953, which is also mixed with main unblanking pulse at emitter of T954. The astigmatism is adjusted with VR851, applied on grid G2 and G4 of CRT. The geometry voltage is adjusted with VR852, applied on grid G5 of CRT. Component Tester : The Component Tester circuit functions for test of active and passive components. Basically, this circuit functions like lissajous figures in XY mode. For, this purpose, 10V AC input is taken from mains power transformer. The X input is voltage scale and Y input is current scale. The X output is applied through R1 0 to X final amplifier. The potential is approximately 8.6Vrms, which appears at CT terminal open circuit. When a component active or passive is connected to CT terminal a load current flows through component, which develops a potential signal proportional to current through component under test. The potential signal is then fed to Y preamplifier via preamp FET 101. The voltage v/s current characteristic is drawn on CRT screen. The samples of patterns are enclosed earlier in figure 5. Calibrator Output : The calibrator output is mainly used for compensating the probe capacitance to that of Oscilloscope. Here, four Nand gates from IC701 are used to make astable multi-vibrator. The output of multi-vibrator is then adjusted for required output of 0.2 V with the help of VR 701 The astable frequency is approximately 1 KHz. Power Supply : The electrical power required by different circuits is being made available thru power supply circuit, which draws power from mains through power transformer. Primarily, the different voltages needed by circuits are as follows: 1. -1900 V 2. +260 V 3. +145 V 4. 33 V 5. +24 V 6. 12 V 7. +12 V 8. +5 V 9. 6.3 V 10. 10 VAC

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1. -1900 Volts P.S. This is a series regulator. A 480V AC input is made to approximately 2400-2500V, by using two double connected in series as shown in circuit. The output voltage is sensed by R908 and other resistors to pin no. 3 of op-amp IC 901, which in turn regulate the base current of transistor bank T901, T902 and T903 which drops the excess voltage across them. Thus, -1900 V is regulated.

2. +145 V P.S. This is a series voltage regulator where the output is controlled by transistor T802 (BF458). The base drive of T802 is adjusted by VR801 (47KOhm) preset to get +145V power supply output.

3. +260 V P.S. This power supply is based on, the output of +140 V power supply. The additional +120 V is added with the help of transistor T801, where base drive is precisely maintained by zener diode D801 (120 V). Hence adjusting +140V, means also adjusting for +260 V.

4. 33 V P.S. A 35 Volts AC secondary output is first rectified by diode D957 and controlled by zener 33 V connected in CRT circuit, for 33 Volts supply for unblanking circuit.

5. +24 V P.S. A full wave rectified DC output is regulated by voltage regulator IC 801, output voltage can be checked at TP61.

6. - 12 V P. S. A full wave rectified DC output is regulated by voltage regulator IC 803. Output voltage can be checked at TP55.

7. +5VP.S. A full wave rectified output is regulated by voltage regulator IC802. Output voltage can be checked at TP58.

8. 6.3 V AC P.S. This supply is taped by 35-0-6.3 V secondary winding of transformer, for CRT filament heating.

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Calibration Procedure The calibration procedure is a set of logically sequenced instruction to return the instrument to conformance with performance/specification.

Warning ! The instrument must be disconnected from the mains power supply whenever you open the bottom case, repair or exchange the parts.

High Voltage Warning : Hazardous high voltage of up to -2000 V is inside this instrument. The transparent protective cover over the EHT circuit should not be opened, refer service to authorized service personnel only.

Service and Adjustment : Of this instrument should only be performed in accordance and in conjunction with operating manual and the warranty contained there in, particularly section service instruction and operating instruction should only be performed under guidance of qualified and experienced personnel. This is particularly important in adjustments in the High voltage section of the instrument.

Test Instruments required : 1. Amplitude Calibrator or Scope Tester Hz 60.

2. Constant Amplitude Sine Wave Generator 20 Hz to 20 MHz

3. Time mark generator from 0.5 µs/Div to 0.2s Div. 4. Pre-attenuator 2: 1.

5. 50 Ohm BNC through Termination. 6. 2 BNC to BNC cables.

7. Oscilloscope probe 10:1 8. 4 ½ Digital Multimeter.

9. Oscilloscope 20 MHz 10. Trimming & Adjusting Tools.

11. Variable output insulation transformer. The procedure covers all calibration and the most important performance checks. The current sequence of all calibration steps must be strictly followed.

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Adjustment Steps 1. Trace Rotation Check: Potentiometer 751

a. Locate & identify potentiometer 751 on Trace Rotation section. Using Y Pos and X pos controls move base.

b. Line to the centre of the graticule. c. When turning P951, check that the range of inclination of the base line is at

least 2mm at both horizontal limits of the graticule. d. Readjust base line exactly parallel to the horizontal centre line of the

graticule.

2. Power Supply : +24 V : Locate and identify check point no. TP61. Check and verify +24V. +5 V : Locate and identify check point no. TP58. Check and verify +5V.

+12 V : Locate and identify check point no. TP72 & TP73 Check and verify +12 volts.

-12 V : Locate and identify checkpoint No TP55, Check and verify -12V. +145 V : Locate and identify check point No TP52, and preset VR 801. Adjust

VR 801 for +145V +260 V : Locate and identify check point No.TP51 Check and verify + 260

volts approximately -1900 V : Locate and identify check point No TP69 Check and verify -1900

Volts approximately Caution! High voltage present here !

3. Max. & Min. Intensity of CRT : VR 901 & VR 902 a. Locate and identify VR 902.

b. Set base line in centre. c. Set intensity control to fully clockwise position.

d. Push Auto/Norm - Push button, a dot appears. e. Adjust VR901 (max.) so that the dot just disappears.

f. Release 'Auto/Norm' Push button. g. Set intensity control to fully counter clockwise position.

h. Push X-Y button, a dot appears. i. Set VR902 (Min) so that a dot just disappears. Release X-Y button.

j. Repeat the procedure.

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4. Astigmatism: VR 851 a. Set baseline in centre. b. Push X-Y push button, a dot appears. c. Set intensity control to optimum sharpness of the dot . d. Adjust VR 851 so that while varying focus control left and right, dot must

be round and sharp at middle position of the focus control. e. Release X-Y push button.

5. Geometry: VR 852 a. Connect 8 Div sine wave input, adjust Y-Pos control so that the display is

equal to 8 division graticule line. b. Now adjust VR852 , such that first and last sine wave shape is maintained,

also the top and bottom c. Peak over 10cm remains same.

6. Un-blanking : VR 951 a. Set the Oscilloscope to CH I mode and input to AC coupling. b. Feed 50 KHz sine wave input to CH I. c. Adjust VR 951 so that when rotating time base switch, retrace should not

be seen with sine wave signal. d. Set intensity to medium.

7. Symmetry: VR 101 a. Set the Oscilloscope to CH I mode, and Input to AC coupling. b. Feed sine wave signal of sufficient amplitude and adjust VR101 so that

when Y position is changed to up or down, the trace becomes symmetrical with respect to centre.

c. Repeat the procedure for CH II symmetry. 8. Trigger Symmetry And Threshold :

a. Set the Oscilloscope to CH I mode and Input coupling CH I to AC. b. Feed 5 KHz sine wave signal and take 4mm height. c. Adjust VR 401 so that when +/-switch is operated the triggering remains

stable. Check the same in CH ll.

9. Sweep Length: VR 402 a. Set base line in centre. b. Adjust VR 402 for trace length 10 Div. AC. c. Shift trace 1 Div. towards left. d. Again adjust VR 402, so that trace length increased to 10.8 cm.

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10. X Centre & 142 Volt Adjustment : VR351 & VR 501 a. Set the baseline exactly at the centre of the horizontal graticule line.

b. Push XY-button, a dot will appear. c. Adjust VR 351 to bring the dot at the centre of the CRT graticule.

d. Adjust VR 501 for 142 volt at test point TP38 and TP39.

e. Release XY button.

11. DC Balance of Y Pre Amp : VR 210 & VR 211 a. Locate and identify VR 210

b. Set Oscilloscope in dual mode. c. Adjust preset VR 210 so that when CH II trace is shifted vertically across

the entire screen, the position of other trace must not vary by more than 0.5 mm.

d. Adjust preset VR 211 so that when CH I trace is shifted vertically across the entire screen the position of other trace must not vary.

12. Y-Gain Ch I: VR 203 a. Locate and identify VR 203.

b. Set the Oscilloscope to CH I mode. c. Set the Input attenuator to 5mV/Div.

d. Connect 1 KHz square wave signal of 25 mV magnitude via 50 Ω through termination to Input of CH I.

e. Adjust preset VR 203 for 5 Div. display height.

13. Y-Gain CH II : VR 204 a. Locate and identify VR 204.

b. Set the Oscilloscope to CH II mode. c. Repeat the procedure as under step no.12 for CH I

14. Ext X Gain : VR 207 a. Locate and identify VR 207.

b. Set the Oscilloscope to CH I mode. c. Push X-Y push button.

d. Connect 1 KHz square wave signal of 25mV magnitude via 50 Ω through termination to Input of CH II.

e. Set the CH II input attenuator to 5mv/Div. f. Set Input coupling of CH I to Gnd and CH II to DC.

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g. Adjust preset 207 so that the distance between the two points on the screen is 5 Div.

h. Release X-Y push button.

15. Attenuator Compensation Ch-I VC 101,102,103,104 …….110 : a. Locate and identify the above mentioned trimmers on CH I attenuator for

this, refer to adjusting plan.

b. Release all push button out. c. Set Input coupling switch CH I to DC.

d. Set Input attenuator to CH I to 5mV/Div. e. Set amplitude calibrator to 5 KHz (approx) with good flat top and feed it to

input of CH I. f. Keep 4 Div display height on each range.

g. Adjust respective trimmers as mentioned below for flat top square wave.

Range 5 mV

10 mV

20 mV 50 mV

100 mV 200 mV

500 mV 1 V

2 V 5 V

10 V 20 V

Trimmer No adjustment

VC 108

VC 110 VC 102

VC 107 VC 109

VC 104 No adjustment

No adjustment VC 106

No adjustment No adjustment

Recheck compensation in all attenuator positions.

• Set again input attenuator CH I to 5mv/Div.

• Connect the output of the calibrator via BNC to BNC and 2:1 pre-attenuator to the input of CH I

• Adjust trimmer in 2:1 pre-attenuator for flat top square wave.

• Keep 4 Div. display height on each range.

• Adjust compensation as below :

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Range Trimmer 50 mV/Div VC 101

0.5 V/Div VC 103 5 V/ Div VC 105

Attention ! The setting of the trimmer in the 2:1 pre-attenuator must not be changed during the compensation, adjustments of the same channel. Repeat the compensation procedure for CH II as under CH I.

16. Time Base Speed Adjustment : VR 403, VC 401 : a.

i. Locate and identify VR 403 on Timebase circuit.

ii. Set time base switch to 50µs/ Div and time base variable control to Cal position.

iii. Set time mark generator to 50 µs/ Div and connect signal to CH I input via 50 Ω through termination

iv. Move the trace with X position control so that the first time mark coincides with first left graticule line of the screen.

v. Adjust VR 403 so that the 11th time mark coincides with the last right graticule line.

vi. Rotate time base variable control to fully clockwise position, signal should be magnified 2.5 times.

b. i. Locate and identify VC 401 in time base circuit.

ii. Set time base switch to 0.5 µs & time base variable to Cal position.

iii. Set time mark generator to 0.5 µs/ Div iv. Move trace with X position control so that the 1st time mark coincides

with the first left graticule line of the screen.

v. Adjust VC 401 so that the 11th mark coincides with the last right graticule line.

c. i. Set time base switch to 5 ms/cm and time base variable to Cal position.

ii. Set time mark generator to 5 ms/cm. iii. Move trace with X-Position control so that the first time mark coincides

with the first left graticule line of the screen.

ST2001E


iv. Add capacitor in parallel, with C419 so that, the 11th mark coincides with the last graticule line.

v. Check accuracy on all ranges by moving time mark generator switch and time base switch simultaneously. All ranges should be with in 3%.

17. Y Response And Square Wave Adjustments VR 251, VR 252, & VC 551 and VC 101 : a. Locate and identify VR 251, VR 252, VC 551 on Y final circuit. b. Set Input attenuator to 5mV/ Div.

c. Connect a 1 MHz square wave signal of 25 mV amplitude via 50 Ω cable & 50 Ω through termination from scope tester to input CH I.

d. Adjust VR 551, VR 552 and VC 551 for steep leading edge and minimum overshoot.

e. Repeat until optimum is obtained.

f. Push CH I / CH II and Trig 1/Trig 2. g. Set input attenuator CH II to 5mV/ Div.

h. Connect 1 MHz square wave signal of 25mV amplitude via 50 Ω cable &. 50 Ω through termination from scope tester to input CH II.

i. Check square. wave response for steep leading edge and minimum overshoot. Otherwise adjust with above mentioned preset and trimmer.

j. Square wave response of both channels should be same. For that, if required, adjust the overshoot with VC 101 on Y pre amp of each channel. Otherwise keep VC101 in max position.

18. Component Tester Y Position Adjustment: VR 1 : a. Locate & identify VR1 in component tester circuit.

b. Keep the instrument in CH I mode. c. Using Y Pos. and X Pos. controls move baseline to the centre of the

graticule. d. Push CT push button.

e. A horizontal line of approximately 6 to 7 Div. length will appear on the screen. Align this trace to the centre graticule line with VR 1.

f. Short the CT terminal with ground. g. A vertical line of 4 to 5 Div. height should be visible.

ST2001E


19. Calibrator Voltage Adjustment: VR 701 : a. Locate and identify VR 701 and test point TP40 on calibrator circuit.

b. Set the instrument in CH I mode. c. Set the input attenuator to 50mV/ Div.

d. Take the probe and connect the TP40 cal output to the input of CH I.

e. Adjust VR 701 for 4 Div. display height.

f. This 0.2 V calibrator output can be checked and verified in the other Oscilloscope.

20. Check Auto/level Function: a. Connect 50 KHz sine wave signal to the input of CH I.

b. Set attenuator Y volts/ Div, so that 3-4 Div. Display is on the screen. c. The display signal should be triggered.

d. When Auto/Level S404 is pressed, a Level control P-401 is used on either direction, the signal should be triggered on-90 to + 90° phase, and after these limits there should be no trace.

21. Check 5 Vpp Sweep out put: TP33: a. Take probe and connect the test point TP33 (sweep output) to another

Oscilloscope. b. The peak to peak sweep output should be between 4.8 V to 5.2 V.

22. Check The Y Bandwidth: a. Select CH I mode, AC coupling.

b. Connect 50 KHz sine wave signal from constant amplitude generator to the input of CH I via 50 Ω BNC to BNC cable and 50 Ω through termination.

c. Set the input attenuator to 5mV/ Div.

d. Adjust the height of the display to 6 Div height.

e. Change the frequency of input to 20 MHz f. The height of the signal should be more than 4.2 Div.

g. Then the bandwidth is said to be more than 20 MHz h. Repeat the procedure for CH II.

23. Check The X-Band Width: a. Set the Oscilloscope to CH I mode.

b. Set input coupling of CH I to Gnd and CH II to DC. c. Set the base line in the centre of the CRT graticule.

d. Set the CH II attenuator to 5mV/ Div.

ST2001E


e. Connect 50 KHz sine wave signal from constant amplitude generator to the input of CH I, via 50 Ω BNC to BNC cable and 50 Ω through termination.

f. Push XY pushbuttons, a horizontal line will be visible. g. Adjust the length of the line to 6 Div.

h. Change the frequency of input to 2 MHz i. The displayed length of line should be more than 4.2 Div.

j. Than band width of X is said to be more than 2 MHz.

24. Check The Trigger Bandwidth: a. Set the Oscilloscope to CH I mode and input to AC coupling.

b. Connect 30 MHz sine wave signal from constant amplitude generator to the input of CH I via 50 Ω through termination.

c. Adjust the height of the display to 1 Div height. d. At one Div. height, signal should be triggered.

e. Then the bandwidth is to be said as more than 30 MHz.

Service Instructions

General : The following instructions are intended as an aid for the electronic technician, who is carrying out readjustment on the ST2001E, if the nominal values do not meet the specifications. These instructions primarily refer to those faults, which were found after using the test instructions. However, this work should only be carried out by properly qualified personnel. For any further technical information call or write to Scientech Technologies Pvt. Ltd., addresses are provided at the back of the manual. It is recommended to use only the original packing material, should the instrument be shipped to us for service or repair (see also warranty and dispatch procedure).

Instrument Case Removal : The bottom cover can be taken off after unplugging the power cord's triple-connector and after eight counters sunk screws and two bottom screws have been removed.

Caution ! During opening or closing of the bottom case, the instrument must be disconnected from all power sources for maintenance work or a change of parts or components. If a measurement, trouble-shooting or an adjustment is unavoidable, this work must be done by a specialist, who is familiar with the risk involved. When the instrument is set into operation after the case has been removed, attention must be paid to the acceleration voltage for the CRT-2000 V and to the operating voltages for both final amplifier stages -145 and 260V. Potentials of these voltages are

ST2001E


on the CRT socket and on the main board. Such potentials are moreover on the check points. They are highly dangerous and therefore precautions must be taken. It should be noted furthermore that short occurring on different points of the CRT high voltage and unblanking circuitry will definitely damage some semiconductors and the opto-coupler. For the same reason it is very risky to connect capacitors to these points while the instrument is on.

Capacitors in the instrument may still be charged, even when the instrument is disconnected from all voltage sources. Normally, the capacitors are discharged 6 seconds after switching off. However, with a defective instrument an interruption of the load is not impossible. Therefore, after switching off, it is recommended to connect one by one all terminals of the check points on the PCB across 1KOhm to ground (chassis) for a period of 1 second.

Handling of the CRT needs utmost caution. The glass bulb must not be allowed-under any circumstances to come into contact with hardened tools, nor should it undergo local superheating (e.g. by soldering iron) or local under cooling (e.g. by cryogenic-spray). We recommend the wearing of safety goggles (implosion danger).

Operating Voltages : Besides the two AC voltages for the CRT heating (6.3 V) and component Tester (12V) there are ten electronically regulated DC operating voltages generated (+12 V, +24 V, +5V,-12 V,+260 V,+145 V and 33 V for the unblanking circuit). These different operating voltages are fixed voltages, except the +145 V which can be adjusted.-1900 Volts is dependent on the accuracy of +12 V and -12 V supply (and also from some resistors with close tolerances). 33 V in the unblanking circuit is stabilized with Z-diode. The variation of the fixed voltages greater than ±5% from the nominal value indicates a fault. Except 33 V, +145 V, and -1900 V, the other DC Voltages have no more than ± 2% variation on the average. These voltages are measured on the checkpoint with reference to ground. Measurements of the high voltage may only be accomplished by the use of a sufficiently high resistive voltmeter (>10M Ω). You must make absolutely sure that the electric strength of the voltmeter is sufficiently high. The 33 V for the unblinking circuit can be measured as the difference between two high voltages with reference to ground. It is recommended to check the ripple and also the interaction from other possible sources. Excessive values might be very often the reason for incomprehensible faults.

Maximum and Minimum Brightness :

Two variable resistors of 500 K Ω each, located on the EHT socket are used for these adjustment procedures (see Adjusting Plan). They may only be touched by a properly insulating screwdriver (Caution! High voltage). The adjustments may possibly have to be repeated, because the functions of both variable resistors are dependent on each other. Correct adjustment is achieved, when the trace can be blanked while X-Y pushbutton is pressed and in addition, when the requirement described in the Test Instructions are met.

ST2001E


Astigmatism control : The ratio of vertical and horizontal sharpness can be adjusted by the variable resistor of 50K Ohm located on the Astig circuit section (see Adjusting Plan). As a precaution however, the voltage for the vertical deflecting plates (approximately +100V) should firstly be checked because this voltage will affect the astigmatism correction. The correction should be repeated several times in this sequence. The adjustment is finished, when the Focus knob excessively brings no improvement of the sharpness in both directions.

Trigger Threshold : The internal trigger threshold should be in the range of 5 to 6 mm display height. It is strongly dependent on the 529 CN comparator IC If there are compelling reasons to replace this comparator, it may be that triggering becomes too sensitive or too insensitive caused by the IC gain tolerances (please refer calibration procedure).

Trouble-shooting the Instrument : For this job at least an isolating variable mains-line transformer (protection class II), a signal generator, an adequate precise multi meter, and if possible Oscilloscope are needed. This last item is required for complex faults, which can be traced by the display of signal or ripple voltages. As noted before, the regulated high voltage and the supply voltage for the final stages are highly dangerous. Therefore it is recommended to use totally insulated extended probe tips, when trouble shooting the instrument. Accidental contact with dangerous voltage potentials is then unlikely. Of course, these instructions cannot thoroughly cover all kinds of faults. Some common sense will certainly be required, when a complex fault has to be investigated. If trouble is suspected, visually inspect the instrument thoroughly after removal of the case. Look for loose or badly contacted or discolored components (caused by overheating). Check to see that all circuit board connection are making good contact and are not shorting to an adjacent circuit. Especially inspect the connections of the power transformer to main PCB, to CRT socket, and to trace rotation coil (inside of CRTs shielding). Further more the soldering connections of the transistors and fixed three terminal regulators respectively on the rear chassis. This visual inspection can lead to success much more quickly than a systematic fault location using measuring instruments. Prior to any extensive troubleshooting, also check the external power source. If the instrument fails completely, the first and most important step-after checking the mains/line voltage and power fuse will be to measure and deflecting plate voltages of the CRT.

While the measurement takes place, the position controls of both deflection devices must be in mid position. When the deflection devices are operating properly, the separate voltage of each plate pair are almost equal. If the separate voltages of a plate pair are very different, the associated circuit must be faulty. An absent trace in spite of correct plate voltages means a fault in the CRT circuit. Missing deflection plate voltages is probably caused by a defect in the power supply.

ST2001E


Replacement of Components and Parts : For the replacement of parts and components use only parts of the same or equivalent type. Resistors without specific data in the diagrams have a power dissipation of 0.33 Watt and a tolerance of 2%. Circuit must have sufficient electric strength. Capacitors without a voltage value must be rated for an operating voltage of 63 V. The capacitance tolerance should not exceed 20%. Many semiconductors are selected, especially the gate diodes 1N4154, and all amplifier transistors, which are contained in push-pull circuits (including the FETs). If a selected semiconductor is defective, all gate diodes or both push-pull transistors of a stage should be replaced by selected components, because otherwise there are possibly deviations of the specified data or functions.

Replacement of the Power Transformer : It should be necessary colour to replace the mains/line transformer, the correct terminal sequence (color identification) for primary and secondary windings must be followed (see diagram "Power Supply"). In addition the relevant Safety Regulations must be observed. Here, we refer only to those requirements relative to the parts conductivity connected to the supply mains: 1. The construction of the instrument shall be such as to prevent any short

circuiting or bridging the insulation, clearances or creep age distances between those parts connected to the supply mains and any accessible conductive parts due to accidental loosening or freeing of the wiring, screws etc.

2. The minimum cross section of the protective earth connection between the instruments power inlet and the connecting soldering tab on the rear chassis must be 0.81 mm2.

3. Connecting soldering tab on the rear chassis has to be secured mechanically against loosening (e.g. with lock washer).

After replacing the power transformer, all remaining bits of wire, solder and other foreign matter must be removed from the PCB's, the vicinity of the power transformer and from within the insulting connecting box by shaking, brushing and blowing. Finally, the top plate of the insulating connecting box has to be replaced. Before connecting the instrument to the power supply, replace the possibly defective fuse, press the Power button and make sure that there is an adequate insulation state between chassis (safety earth conductor) on the one hand, and the live/line pin as well as the neutral pin, on the other. Only after proper insulation has been established may further function tests with open chassis follow, but with appropriate precautionary measures.

ST2001E


Part List Circuit Descrip PCB Circuit Circuit Description PCB Circuit Part tion Loc- Schematic Part Loc- Schematic Ref. ation Location Ref. ation Location Resistors R205 470R G3 E9 R206 150R H2 D9

R001 51R 1/4W N4 E2 R207 390R H2 D9 2 % CFR R211 820R H4 E8

R003 68K P8 J2 R212 51 R H4 E8 R004 470R N7 J1 R213 820R H4 F8

R005 100K P10 K1 R214 150R H4 F9 R006 470R M10 N14 R215 470R G4 F9

R1 1K5 N1 N2 R216 150R G4 F9 R2 10K P1 N2 R217 390R G4 F9

R3 150K N1 N2 R251 51 R G2 E10 R4 150K N1 N2 R252 51 R G2 F10

R5 1M P1 N2 R253 2K2 G1 F10 R6 6R8 M2 N2 R254 2K2 G1 F10

R7 680R N3 N2 R255 8K2 H1 E11 R8 390R N3 N2 R256 8K2 H1 F11

R9 680K P2 M2 R257 12K H1 F11 R10 100K P1 M2 R258 12K H1 F11

R11 47K F1 N3 R259 6R8 K1 G11 R101 33R F1 F3 R260 22K K1 F12

R102 898K F1 F2 R261 15K K2 F13

R103 111K F1 G2 R262 22K M2 F13

R04 988K F1 G2 R263 15K M1 F13 R105 10K1 F1 G2 R264 15K M2 F13

R106 1M F1 G2 R265 2K2 M3 G13 R107 10K1 F1 H2 R266 22K K2 E12

R108 499K F1 G4" R267 10K K2 F13 R109 1M F1 G4 R268 1K M1 F13

R110 750K F1 G4 R269 100R K2 F13

ST2001E


Circuit Descrip PCB Circuit Circuit Description PCB Circuit Part tion Loc- Schematic Part Loc- Schematic Ref. ation Location Ref. ation R112 1M F1 F5 R351 150R 12 F8

R113 220K F1 F5 R352 6R8 H4 G8

R114 330R M4 H5 R353 150R 12 G8

R115 330R M4 G5 R354 1K5 13 G9 R116 330R M4 F5 R355 1K5 13 G9

R117 330R M4 E6 R356 270R 13 G9 R118 6R8 K5 E7 R357 1K5 J4 G9

R119 51R M4 F6 R358 6R8 14 G9 R120 6R8 K3 F7 R359 1K5 14 G9

R121 100R K4 G6 R360 6R8 H5 H8 R122 470R K4 G6 R361 6R8 H5 H8

R123 150R K4 H6 R362 150R 14 G8 R124 22K K4 G6 R363 1 K5 J5 H9

R125 6R8 K4 H7 R364 1K5 15 H9 R201 820R H2 D8 R365 150R 15 H9

R202 51 R H2 E8 R366 1K5 15 H9 R203 820R H2 E8 R367 6R8 H5 H9

R204 470R G2 D9 R368 1K5 H5 G9 R369 10K 17 G10 R442 51 R G9 J6

R370 3K3 H6 G10 R444 51 R H7 M3 R371 2K2 N7 H11 R445 27K H7 M3

R372 3K3 H6 G10 R447 470R G7 M4

R373 10K J6 H10 R500 10K F3 N4

R374 820R N7 G12 R501 62K F3 N4 R375 18K N7 G12 R502 6R8 E2 N4

R376 62K M7 G13 R503 2K7 E3 N4 R377 3K3 K7 G13 R504 6R8 E1 N5

R378 33K K7 G13 R506 6R8 D1 M5 R379 51R M8 G13 R507 365R E1 N5

R380 1K2 M7 H13 R508 365R E1 N5

ST2001E


Circuit Descrip PCB Circuit Circuit Descrip PCB Circuit Part tion Loc- Schematic Part tion Loc- Schematic Ref. ation Location Ref. ation R401 100K N9 K1 R509 68R E2 N5

R402 10K N10 K2 R510 100 + E2 N5

R403 33K N8 K2 68R

R404 33K N8 K2 R511 180R E3 N5 R405 1M K8 J2 R512 4K7 E3 N5

R406 470R K8 J2 R513 10K E3 N6 R408 1 M5 N10 J2 R514 15K, 4W E2 M6

R409 1M M9 K2 R515 15K, 4W F2 N6 R410 51R 110 K3 R516 51 R F3 N4

R411 680R N9 K2 R517 12K F3 N3 R412 3K3 M10 K2 R518 6R8 F3 M3

R413 6R8 17 K3 R519 6R8 F3 N4 R414 470R M9 13 R520 6R8 To CRT M6

R415 4K7 M9 13 Plate R416 10K M9 13 R521 6R8 -do- N6

R418 47K K9 13 R551 68R F5 D10 R419 51 R K9 K3 R552 68R F5 E10

R420 51R 110 K3 R553 9K1 C4 D10 R421 1K H 10 K4 R554 51 R D4 D11

R422 100K 110 J4 R555 51 R C4 E11 R423 10K M10 K4 R556 7K5 D4 D11

R424 10K J8 K4 R557 470R D3 D11

R425 10K J9 J4 R558 470R C3 E11

R426 10K J8 K4 R559 6R8 D4 E11 R427 51 R H7 K4 R560 51 R D3 D12

R429 200K H8 M5 R561 51R C3 E12 R430 6R8 G6 M5 R562 1K2 D3 D12

R431 10K H8 J5 R563 1 K2 C3 E12 R432 20K H8 J5 R564 68R D3 D13

R433 40K2 H8 K5 R565 68R C2 E13

ST2001E


Circuit Descrip PCB Circuit Circuit Descrip PCB Circuit Part tion Loc- Schematic Part tion Loc- Schematic Ref. ation Location Ref. ation R434 100K H8 K5 R566 180R D2 E13

R435 200K H9 K5 R567 68R D2 D13

R436 402K H9 K5 R568 68R C2 E13

R437 4K7 F8 M6 R569 39K C1 D13 R438 22K G8 M6 R570 100R D2 D13

R439 33K F9 M7 R574 2K4, 6W D2 D14 R440 2K2 F10 K7 R575 1K D2 D14

R441 180R G10 17 R576 1K C2 E14 R577 2K4 6W C1 E14 R956 51R C7 K13

R601 470R G5 M12 R957 150K C7 113 R602 470R G6 M4 R958 51R C6 K13

R702 47K E5 M12 R959 3K3 F7 M13 R703 47K 05 N13 R960 470R E7 M13

R704 15K 05 N13 R961 33K E7 M13 R705 15K 05 N13 R962 47K F7 M13

R706 270R C5 N14 R751 470R E5 N13 Capacitors

R752 470R F5 N13 C001 0.1uF, P4 E2 R801 4K7 A6 110 400V MP

R802 470R A6 110 C003 68pF DISC P8 J2 R803 1K5 A5 K10 500V

R804 5 10R A2 K9 C004 0.33uF MP N8 J2

R805 56K A2 K9 100V

R806 91K B4 K10 C005 1uF, 100V N8 11 R807 33K+ A2 K10 MP

33K C1 0.1uF N1 N2 R808 51 R A3 M9 400V MP

R809 7K5 A3 M9 C2 2.2uF 63V N3 N2 R810 51 R B4 M10 MP

ST2001E


Circuit Descrip PCB Circuit Circuit Descrip PCB Circuit Part tion Loc- Schematic Part tion Loc- Schematic Ref. ation Ref. ation R811 100K B4 M10 C101 5.6pF Attn. G2 R812 33K A4 M11 DISC Assembly R851 68K A2 K14 500V R852 47K B1 K14 C 102 2.2pF -do- F2 R853 100K B1 114 C103 5.6pF -do- G2 R854 47K B1 114 C104 8.2pF -do- G1 R901 10K 08 N9 C105 100pF -do- G2 R902 1K E10 N9 C106 6.8pF -do- H1 R903 750K E10 N10 C107 1300pF -do- H2 R904 750K E10 N10 STY100V R905 750K E10 N10 C108 8.2pF500V -do- F4 R906 1 M+ 1 M E8 N10 DISC R907 6M8 07 N9 C109 1.2pF -do- G4 R908 9K1 E8 N10 C110 10nF 400V -do- F5 R909 47K E8 N11 MP R910 18K E8 N10 C111 22nF DISC M5 E5 R911 1K E9 N10 30V C112 1nF 500V M4 F5 R912 1M E9 N10 DISC R913 390R F9 N11 C113 22nF DISC M3 H5 30V R914 1M E9 J11 C114 0.1uF 50 V M3 H6 ML R915 1 M5 E8 J12 C116 10uF 40V M5 G6 R916 1 M8 E7 112 ELEC R917 220K+ C6 K12 C 117 0.1uF 50V K4 G6 100K ML R951 10K C8 M9 C118 22nF DISC M3 F6 R952 1 M5 07 K12 C415 2.2uF 63V H9 K5 ELEC R954 10K C7 K13 R953 1M C8 K13 R955 15K E7 K13 30V

ST2001E


Circuit Descrip PCB Circuit Circuit Descrip PCB Circuit Part tion Loc- Schematic Part tion Loc- Schematic Ref. ation Location Ref. ation C119 10uF M3 F6

ELEC 40V C416 0.1uF 50V F8 K6

C120 0.1uF 250V K5 F6 ML

MP C417 180pFSTY G10 17 C201 27pF DISC H2 E9 100V

500V C418 24400pF G10 17 C211 27pF" H4 F9 STY 100V

C251 22nF DISC H1 E11 C419 2.2uF 63V 010 K7 30V MP

C252 10uF, 40V H1 E11 C421 470pF G7 M4 E1EC DISC

C253 3.9pF H1 F19 500V DISC C422 220pF H10 M5

500V STY 100V C254 3.9pF 11 F11 C423 220pF F9 K7

DISC DISC 500V 500V

C255 22nF DISC 11 F12 C501 0.1uF 50V F2 N3 30V ML

C256 10uF, 35V J2 F12 C502 0.1uF F2 N4 ELEC C503 330pF E2 N5

C257 220pF M1 F13 STY 100V

DISC C504 1.8nF " E2 N6

500V C505 0.1uF 50V F3 N4 C258 470pF" K3 F13 ML

C351 15pF DISC M7 G12 C506 68p FDISC E 1 N5 500V 500V

C401 0.33uF p8 J2 C551 22nF DISC D3 D11 100V MP 30V

ST2001E


Circuit Descrip PCB Circuit Circuit Descrip PCB Circuit Part tion Loc- Schematic Part tion Loc- Schematic Ref. ation Location Ref. ation C402 6.8pFDISC N9 K2 C552 10uF, 40V C3 D12

500V ELEC

C403 6.8pF" N8 K2 C553 4700p STY C1 E13

C404 10uF 40V N10 K2 100V ELEC C554 47pF DISC C2 E13

C405 0.1uF 50V K8 K3 500V ML C555 68pF, DISC C2 Dl3

C406 1uF, 35V M9 13 500V T ANT AL- C601 47uF, 25V G5 M12

UM ELEC C407 1uF 35V" K9 13 C602 47uF, 35V F6 M3

C409 22nF DISC M10 13 ELECT 30V C702 22nF DISC D5 N12

C411 0. 1uF H 10 J4 30V 50V ML C703 10uF, 40V D5 N12

C412 100uF 35V F7 M5 ELEC ELEC C704 470pF D4 N13

C414 22nF DISC J8 K5 DISC 30V 500V

C705 10nF 160V D5 N13 MP 100V MP

C801 1000uF B6 J9 C910 0.01uF, C6 K12

50V ELEC 400V MP

C802 22nF DISC A7 110 C951 10uF, 63V C8 M9 30V ELEC

C803 I0uF, 40V A7 110 C952 0.1uF 50V C7 M10 ELEC ML

C804 1000uF, B5 J9 C953 100pF, D7 M12 25V ELEC 2KV DISC

ST2001E


Circuit Descrip PCB Circuit Circuit Descrip PCB Circuit Part tion Loc- Schematic Part tion Loc- Schematic Ref. ation Location Ref. ation C805 22nF DSC A6 110 C954 100pF, D8 K13

30V 2KV DISC

C806 10uF, 40V A6 J10 C955 100pF, D8 K13

ELEC 2KV DISC C807 1000uF, B5 K9

25V ELEC Diode, Zeners C808 22nF DISC A5 K10 D001 LED CHM N14

30V D101 FDH300 M3 F5 C809 10uF 40V A5 K10 D201 1 N4154 G2 D 10

ELEC D202 1 N4154 G2 D9 C810 47uF, 250V B2 K9 D203 1 N4154 G2 E9

ELEC D204 1 N4154 G2 E10 C811 47nF, A3 K10 D205 1 N4154 G4 E10

250V MP D206 1 N4154 G4 E9 C812 47nF " A4 K10 D207 1 N4154 G5 F9

C813 47uF 250V B3 M9 D208 1 N4154 G5 F10 ELEC D251 1 N4154 M2 E14

C814 47nF 250V B4 M10 D252 1 N4154 K2 E14 MP D351 1 N4154 J6 G9

C851 0.1uF, A1 K14 D352 1 N4154 J6 G9 160V MP D353 1 N4154 N7 H9-

C852 0.1uF, B1 114 D354 1 N4149 17 G10

160V MP D355 1 N4154 J6 H10

C901 0.22uF, 1 C8 N9 D356 1 N4154 H6 H11

KVMP D357 1 N4154 M8 H 12 C902 0.22uF, 1 C10 N9 D401 1 N4154 M8 13

KVMP D402 1 N4154 M9 13 C903 0.22uF, 1 C8 N9 D404 1 N4154 M10 K3

KVMP D405 1 N4154 H10 K3

ST2001E


Circuit Descrip PCB Circuit Circuit Descrip PCB Circuit Part tion Loc- Schematic Part tion Loc- Schematic Ref. ation Location Ref. ation C904 0.22uF, C10 N9 D406 1 N4154 J10 J4

1 KVMP D407 1 N4154 J10 J4

C905 100pF, D7 N9 D408 1 N4154 J9 K4-

2KV D501 1 N4154 E3 N5 DISC D801 LED A7 J11

C906 220uF 16V F9 N10 D802 LED A6 J11 ELEC D803 LED A5 K11

C907 0.1uF, 1KV D8 K12 D804 LED A2 K11

MP D806 LED A4 N11 C908 0.1uF, 1KV D10 J11 D901 1N4007 C8 N9

MP

C909 0.33uF D7 K11 D902 1N4007 C9 N9

D903 " C9 N9 T202 BF199 H2 E9 D904 " C10 N9 T203 BF199 G4 E9

D905 " C9 N9 T204 BF199 G5 F9 D906 " C10 N9 T251 BC237B G1 E10

D907 " D10 N9 T252 BC237B G1 F10 D908 " 09 N9 T253 BC237B M2 F13

D909 " D10 N9 T254 BC557B M2 F14 D910 " 08 N9 T315 BC237B 13 F9

D911 " 09 N9 T316 BC237B 13 G9 D912 " 08 N9 T317 BC237B H6 G10 D913 1N4149 F9 N10 T318 BC237B J5 G9 D914 " E9 N10 T319 BC237B J6 H9 D952 LEO C7 K12 T320 BC237B J6 H10 D953 1N4149 07 K12 T321 BC557B M7 G13 D954 " C7 M10 T401 BC237B K10 13 D955 " C7 113 T402 BC237B 110 J4 D957 1 N4007, B7 M9 T403 BC237B H8 K4 1600V T404 BSX19 G9 J6

ST2001E


Circuit Descrip PCB Circuit Circuit Descrip PCB Circuit Part tion Loc- Schematic Part tion Loc- Schematic Ref. ation Location Ref. ation D958 1N4149 ON REAR K13 T405 BC557B G9 K6

SIDE T406 BC239B H7 M3

Z102 ZENER K4 G6 T407 BC237B G7 M3

6.8V T502 BF458 E1 M5 Z403 ZENER K3 K3 T503 BF458 F1 N5

5.6V T504 BC237B E3 N5 Z601 ZENER G5 M12 T505 BC237B F2 N4

12V T551 BF199 04 011 Z602 ZENER G6 M3 T552 BF199 C4 Ell

12V T553 BF199 03 D12 Z751 ZENER F4 N13 T554 BF199 C3 E12

12V T555 BF458 D1 D13 Z805 ZENER A3 K9 T556 BF458 C1 E13

120V T801 BF458 A2 K9 Z915 ZENER 07 K11 T802 BF458 A3 M10

100V T803 BC237B A4 M10 Z956 ZENER C7 M10 T901 BF459 E10 N10

33V T902 BF459 E9 N10 BR801 Bridge A6 J9 T903 BF459 E9 N10

Rectifier T951 BF450 C7 113 B250C1500 T952 BF199 C7 K13

R T953 BC557 E7 M13

BR802 " AS J9 T954 BF450 F8 M13

BR803 " AS K9 BR804 " B2 K9 Trimmers

BR805 " A3 M9 VC101 C ATT. ASS G2 Trimmers

Transistors VC102 ATT. ASS G2 G2 T1 BF450 N1 N2 VC 103 ATT. ASS G2 G2

1/2T1 0 1 A FET U440 M4 F5 VC 104 ATT. ASS G2 G2

ST2001E


Circuit Descrip PCB Circuit Circuit Descrip PCB Circuit Part tion Loc- Schematic Part tion Loc- Schematic Ref. ation Location Ref. ation 1/2T101 B FET U440 M4 G5 VC 105 Attn. assembly G2

T201 BF199 M4 H2 09 VC106 " G2

C107 BF199 M4 H2 IC802 7805 A5 J9

VC108 BF199 M4 04 IC803 7812 A4 K9 VC109 BF199 M4 03 IC901 741 E9 N10

VC110 BF199 M4 04 IC951 CNY-17 C7 112 VC111 2-22 PF K4 H6

VC401 2-20 PF F10 17 Switches and Connectors VC551 2-22 PF C2 Dl4 5405W3 TB 09 17 switch Presets and Pots S252 TB M2 F14

VR01 5K N1 N2 S301 TB H6 01

VR101 25K M4 06 S405W1 TB J9 J5

VR203 500 R 02 E9 switch VR204 500 R H5 F9 S405W2 TB H9 16

VR207 100R H5 H9 switch VR210 250R H3 E9 S1 switch N1 M2

VR211 250 R H3 F9 S101 switch A TT ASS F2 VR351 470R M7 H13 S251 switch K2 F14

VR401 22K K3 J2 S351 switch K7 M3 VR402 500R 07 N4 S403 switch P9 K1

VR403 2K2 08 M6 S404 switch M10 K1 VR501 5K E3 N6 S561 switch F2 M5

VR551 100R C2 E13 S801 ON/OFF CHM K8 VR552 220R D1 E14 switch

VR701 250R C5 N14 S802 MICRO CHM M8 VR801 25K B4 M10 switch

VR851 47K Al K14 S-401 switch P7 11 VR852 47K B1 114 S-402 switch P8 11

VR90 1 470K D6 K12

ST2001E


Circuit Descrip PCB Circuit Circuit Descrip PCB Circuit Part tion Loc- Schematic Part tion Loc- Schematic Ref. ation Location Ref. ation VR902 470K F6 M12 Test Points

VR951 1K E7 K13 TP01 Test M3 F5

P201 500R 03 D9 Point

P202 500R 04 F9 TP02 -do- J2, K3 F7, D8, F8

P401 l0K N10 K2 TP03 -do- 12, K4 08, E8,08

P402 10K 07 M6 TP04 -do- M5 F5

P501 10K E4 N3 TP05 -do- K5.H4 F7, E8.08

P901 470K D5 K12 TP06 -do- K5,H4 07, H8,F8

P902 470K E5 K12 TP07 -do- N3 M2

TRP751 10K F5 N13 TP08 -do- H7,N2 M2

TP09 -do- M4,N2 H5

IC'S TP10 -do- N2 N2

IC401 529 N9 K2 TP11 -do- N2 N2

IC101 592 K3 F6 TP12 -do- G2 E10

IC251 A1/24013 K2 F12 TP13 -do- G1 F10

IC251 B 1/24013 K2 F13 TP14 -do- J6 H9

IC402 A 1/2 K9 K3 TP1S -do- J7 J1,G11

74LS74 TP16 -do- H6 010

IC402 B 1/2 K9 K4 TP17 -do- H6 010

74LS74 TP18 -do- H2 D8

IC701 CD40 11 D4 N13 TP19 -do- H2 E8

IC801 7824 A6 J9 TP20 -do- H4 E8

TP21 " H5 E8 TP73 -do- G5 M12, E7

TP22 " G2 F9 L552 Inductor C3 E14

TP23 " G2 E9 CN1 Connector C6

TP24 " F4 D10 L551 Inductor D2 D14

TP25 " F5 E10 S001 BNC P4 E1

ST2001E


Circuit Descrip PCB Circuit Circuit Descrip PCB Circuit Part tion Loc- Schematic Part tion Loc- Schematic Ref. ation Location Ref. ation Location

TP26 " K8 N2 TP56 BNC A6 J9

TP27 " P7 J2 TP57 BNC A6 J9

TP28 " N9 K2 TP58 BNC A6 F7, J10

TP29 " M9 K2 TP59 BNC A6 J9, N2

TP31 " F8,M3, K9 J4,M12,G14 TP60 BNC A7 J9, N2

TP32 " H8 K4 TP61 BNC A7 J10

TP33 " G7,F3 M4 TP62 BNC B7 M9

TP34 " G9 J6 TP63 BNC B7 N9

TP35 " F2 N4 TP64 BNC B7 M9

TP37 " E3 N4 TP65 BNC B6 M9, K4

TP38 " F1 N6 TP66 BNC C9 N9

TP39 " E1 M6 TP67 BNC C10 N9

TP40 " C4 N9 TP68 BNC E6 M14

TP41 " D4 D10 TP69 BNC B7 M11, M9

TP42 " D4 E10 TP70 BNC E6 M11

TP43 " D1 D14 TP71 BNC D7 K13

TP44 " C1 E14 TP72 BNC G6 M3

TP45 " B1 J14

TP46 " A1 K4 TF1 Transformer CHM J8

TP47 " A2 K9 201

TP48 " A2 K9 F001 FUSE CHM M8

TP49 " A3 M9 350mA,

TP50 " A3 M9 SLOBLO

TP51 " A2 K11 , N7 5x20 mm

TP52 " A4 K11 CRT001 CRT CHM J14

TP53 " A5 K9 Note: CHM : chassis mounted components

TP54 " A5 K9

TP55 " A5 K10

ST2001E


Glossary of Oscilloscope Terms 1. Band width : The range of frequencies within which performance of the amplifier remains within specified limits. Normally this limit is -3dB.

2. Rise time : The time required for the leading edge of the pulse to rise from 10% to 90% of its final value. For Oscilloscope it is given by :

nsMHzin Bandwidth

350rt =

3. Sensitivity : An Oscilloscope sensitivity is described as input signal level needed to produce a stated deflection of the electron beam on the CRT screen. Specifications are given in mV/cm or mV/ Div.

4. Input impedance : The input impedance of Oscilloscope is the value of resistance parallel by capacitance. The attenuators are designed in such way that at any position of input attenuator it offers constant impedance. The typical input impedance of a Oscilloscope is 1MOhm parallel with 25-50 pF.

5. Trigger : In an Oscilloscope, in order to get a stable waveform, it is necessary to synchronize horizontal Time base with the vertical input signal. This synchronization is called Triggering. There are two modes of triggering called Auto and Trigger Level. In the Auto mode, the time base will trigger automatically at the mean level of the input signal. In absence of signal this will give bright base line. In level mode the triggering points can be set at any position of leading edge.

6. Z – modulation : Z-Modulation is nothing but intensity modulation. For a positive TTL level when a '0' volt (low state) is applied, then CRT is blanked. When +5 volt (high state) is applied then trace appears.

7. Maximum input voltage : It is the maximum voltage that can be safely applied to the Y-input of the Oscilloscope. The Oscilloscope demonstrator ST2001E specifies the maximum input voltage to be 350 (DC + peak AC). This means that the voltage of the input, cannot exceed 350 V, which includes both the DC voltage and the peak AC voltage of the signal.

ST2001E


8. Time base : This circuit generates time varying signal which is applied to the horizontal deflection plates of the CRT. The sweep speed is selected on the time base control which is marked in s/ Div., in 1-2-5 sequence. This sequence has been selected because it gives a very good degree of overlap between ranges and thus a test signal can normally displayed on more than one sweep speed. A variable control is also incorporated which increases the sweep speed on any setting and enables the wave form to be expanded.

8. Display modes : The display mode refers to the different possibilities of the signals displaying on screen. In CH I or CH II mode, only signals fed into the CH I or CH II input will be displayed on the screen. In the Alternate mode, the signals from the two channels are displayed alternatively on the screen. In the Chop mode, signals are displayed simultaneously at a chopped frequency (100 KHz in ST2001E). In the X-Y mode, the Oscilloscope is used as a X-Y monitor. Here CH I is Y axis & CH II is X axis.

9. Input coupling : The input switch has three positions, to select either DC or AC coupling or ground. In DC coupling, the input signal is fed directly in to the amplifier while AC coupling enables blocking of the DC components of the input signal and passes only the AC components of the signal to the Y amplifier. In the Gnd position, the input of the Y amplifier is grounded.

ST2001E


Circuit Diagrams

ST2001E


ST2001E


Fault Simulation and Step by Step Fault Finding Procedure

In training and understanding the electronic circuits, a new concept, has been added to ST2001E, where you can create a fault. For creating a fault you can choose any of the 15 different type of standard faults are listed below. You have to simply change one of the shorting shunt / jumper position on to the next position. A complete actual jumper position is shown in jumper position plan. While fault exists, students can go for trouble shooting, and in turn find the fault. The cause of the fault, may be either of short circuited path, open circuited path or base-emitter of transistor short, or collector to emitter is open etc. Once the cause is located, it can be verified and shorting jumper can be placed at right place. In case of difficulty in finding the fault, they can refer to the procedure given below, to locate and analyze it, in systematic step-by-step procedure. Normally, one fault should be inserted, so as to make it simple and problem like in real world. However, one can always, add multiple faults, as desired from the list of the standard faults.

List of Standard Faults : 1. No +24 V Power Supply Present

2. No +5 V Power Supply Present 3. Very Low Channel Gain, in CH I.

4. No gain / signal displayed on screen in CH II. 5. Signal gets distorted as Y pas moved, also gain is low.

6. Trace is in center, no Y shift works. 7. CH I Y-shift is not correct, CH II is correct

8. No chop operation in Dual-Chop mode.

9. No alternate operation in Dual-Alt mode.

10. No trigger from internal source 11. Time Base dead

12. No time base on speeds 0.5µs/cm 50µs/cm and 5ms/cm.

13. No CT , only spot appears on the screen. No trace but, time base ,is present, and shift is correct

14. No trace, but time base is okay. 15. Limited, X position, one sided trace.

Note : For details of test patterns and voltages, please refer to Test Point Details, of this manual.

ST2001E


Procedure of Fault Finding for Simulated Faults Fault 1 : No +24 V Power Supply Present Symptoms : Power LED does not glow, No trace, CT, No Cal

output. D801 does not glow.

Oscilloscope Settings : All push buttons Out, all potentiometers in the centre, time base and attenuators at any position.

Fault Section : Power supply section.

Procedure : 1. Turn ON the instrument. 2. Check voltage at TP61, it should be +24 V, if not then,

3. Check voltage at pin 3 of IC 801, 7824, it should be +24 V, if not then, 4. Check voltage at pin 1 of IC 801, 7824, it should be approximately 33 V, if not

then (If the voltage at pin no.1 is correct, but at pin no. 3 , it is not correct, then the IC is faulty or pin no. 2 is not grounded , or a short circuit in the circuit connected.)

5. Check the voltage at +ve terminal of bridge rectifier BR801, it should be approximately +33V.

6. If the voltage at +ve terminal is correct, then the track between BR801 and IC801 is open.

7. Remove the shorting shunt from pin 2 and 3 and place it between pin 1 and 2 of jumper J1.

8. Turn On the instrument, now you should get +24V at TP61.

Results : As the track between BR801, +ve terminal and IC801 pin 1 was open, +24V was not being generated. By placing the jumper, between pin 1 and 2 of 11, the two points gets, shorted and we get the required power supply of +24 V.

Fault 2 : No +5 V Power Supply Present Symptoms : No trace, No CT , No Cal output Power LED glows,

D802 does not glow. Oscilloscope Settings : All pushbuttons Out, all potentiometers in the centre,

time base and attenuators at any position. Fault Section : Power Supply section.

Procedure : 1. Turn On the instrument.

2. Check voltage at test point TP58, it should be +5V , if not then, 3. Check voltage at pin no. 3 of IC802 , 7805, it should be +5 V, if not then,

ST2001E


4. Check voltage at pin no. 1 of IC802 , 7805 it should be + 12 V, if not then, 5. (If the voltage at pin no. 1 is correct then, IC802 may be faulty or the circuit

connected to it may be short circuited to ground). 6. Check the voltage at +ve terminal of bridge rectifier BR802, it should be

approximately 12 V DC , if not then ,

7. Check the AC input of transformer, which goes to the input AC terminals of bridge rectifier BR802 at test point TP56 - TP57 it should be 9V AC approximately, if not then,

8. (If the AC voltage is correct, but the output of bridge rectifier is still zero, then the bridge rectifier is faulty, or -ve terminal is not getting connected to the ground).

9. Check the AC voltage at test point TP56, it should be 9 V AC.

10. If the voltage is correct, then it is not reaching to the input of bridge rectifier, the track between them may be open.

11. Switch Off the instrument, and remove the shorting shunt from 2 and 3 and place it on at pin 1 and 2 of J2.

12. Switch On the instrument, check the +5 V DC at test point TP58, it should be +5 V, and the instrument should be working.

Results : Due to open circuit between the transformer secondary and bridge rectifier, the ac supply was not reaching the input of bridge rectifier and there was no DC rectified output was available to 7805 IC.

Fault 3 : Very Low Channel Gain CH I. Symptoms : Instead of 5 Div signal, we get 1.5 Div signal height

approximately but when same signal is fed to CH II it displays 5 Div.

Oscilloscope Settings : Connect sine wave signal, 1V pp at 5 KHz, to CH I, set the attenuator to 0.2V/ Div. input coupling to AC.

Fault Section : Y input attenuator Ch I.

Procedure : 1. Check the waveform at TP02 and TP03, compare the waveform with the Test

Point Details given on page 7 of this manual, if it is not correct then,

2. Check that IC 101, 592 is getting proper supplies, + 5Vat pin 10. 3. Check waveform at pin 14 of IC 101, it should be approximately 25mVpp. If it

is not then (If input waveform is correct, but output waveform is not, then IC 101 may be faulty or the gain resistor value may not be correct)

4. Check the drop across D102; it should be approximately 6.8 V.

ST2001E


5. Check voltage at R122, end common to pin 11, it should be approximately 25 mVpp, if not then,

6. Check voltage at pin 11 of IC 101, IC592, it should approximately 25 m V pp. 7. If voltage at pin no. 11 is correct, but at R122, it is not correct, then the track

between, pin no.11 and R122 is open

8. Turn Off the instrument, remove the shorting shunt from pin 1 and 2 of jumper J3 and place it on 2 and 3.

9. Turn On the instrument and check the gain, now, the display should have 5 Div height.

Results : Due open circuit between pin 11 and R122, the gain resistor of the IC 101, 592, the gain was very low.

Fault 4 : No gain / signal displayed on screen CH II. Symptoms : No trace in CH II mode, but Ch I works satisfactory.

Oscilloscope Settings : Connect sine wave signal of 1Vpp at 5 KHz, to CH II. Select CH II. Set attenuator CH II to 0.2V / Div, input to AC.

Fault Section : Y input attenuator CH II.

Procedure : 1. Turn on the instrument.

2. Check the waveform at TP05, TP06 for CH II, compare the signal shape with the details given on page 7 of this manual, if it is not then,

3. Check the waveform at pin 14 of IC 101, IC592, it should be approximately 25 mVpp, if not then (if the voltage, at pin 14, is correct, but the output waveform is not coming, then IC101, 592 may be faulty).

4. Check the waveform at R119, 51R, it should be approximately 25mVpp, if not then,

5. Check the waveform at common end of R119 , and C112 , it should 25 mVpp, if not then,

6. If the voltage at common end of R116 and C 112 is correct, but at R119 it is not correct, then track between two terminals is open.

7. Turn Off the instrument.

8. Remove the shorting shunt from pin 2 and 3 and place it on pin 1 and 2 of J4 . 9. Turn On the instrument, check the waveform at pin 14 of IC 101, signal should

be available. 10. The signal applied should be visible on the screen.

ST2001E


Results : Due to the open track between R 116 and R 119, signal was not reaching the input of IC101. By placing the jumper between pin 1 and 2 of J4, the two points get connected and the fault is removed.

Fault 5 : Signal gets distorted as Y Pos’s are moved in both channels, also gain is low.

Symptoms : Signal gets distorted on top and bottom when moved up and down.

Oscilloscope Settings : Connect sinewave signal, of 1Vpp at 5 KHz, to either input at Ch I or CH II, set the attenuator to 0.2 V / Div and input coupling to AC.

Fault Section : Y final amplifier.

Procedure : 1. Check the waveform at TP43 and TP44, it should be approximately 30 Vpp

if not then,

2. Check the waveform at R564 and R565 , it should be 1Vpp , if not then, (If the waveform at R564 and T565 is correct, but at TP43 and TP44 is not, then either transistor 555 or T556 is faulty or it is not getting proper biasing voltage)

3. Check the waveform at base ofT553 and T554 , it should 1Vpp if not then, (If the waveform at base of T553 and T554 , is correct, but at R564 and R565 it is not, then either T553 or T554 is faulty or it is not getting proper biasing voltage).

4. Check the waveform at TP24 and TP25, it should be 150mVpp approximately, if not then, (If waveform at TP24 and TP25 is correct, but at bases of T553 and T554, it is not, then either T551 or T552 is faulty or not getting correct bias voltage).

5. Check the voltage at R554, end common to R555, R556 and R553, it should be 12V DC.

6. Check the voltage at R553, end common to R554, R556 and R553, it should be +12V DC.

7. If the voltage at R554 is correct, but at R553 it is not, then the track between R553 and R554 is open.


9. Remove the shorting shunt from 1 and 2, of Jumper J5 and place it on pin 2 & 3. 10. Turn On the instrument, and check, now signal is not distorted.

Results : Due to open circuit between, R553 and R554, T551 and T552 were not getting proper bias voltage and hence the trace signal was distorted.

ST2001E


Fault 6 : Trace is in center, no Y shift works, in both the channels.

Symptoms : Y Pos is not working in both the channels. Oscilloscope Settings : Connect sinewave signal, of 1Vpp at 5 KHz, to either

input at CH I or CH II, set the attenuator to 0.2 V / Div and input coupling to AC.

Fault Section : Y final amplifier. Procedure :

1. Check the waveform at TP43 and TP44, it should be 30 Vpp , if not then,

2. Check the waveform at R564 and R565 , it should be 1Vpp , if not then, (If the waveform at R564 and R565 is correct, but at TP43 and TP44 it is not, then either transistors T555 or T556 is faulty or it is not getting proper bias).

3. Check the waveform at base of T553 and T554 , it should be 1 Vpp , if not then, (If the waveform at base of T553 and T554 is correct but at R564 and R565 it is not, then either transistor T554 or T553 is faulty or it is not getting correct bias.

4. Check the waveform at TP24 and TP25 it should be approximately 150mVpp, if not then, (If the waveform at TP24 and TP25 is correct, but at base of T553 and T554, it is not then T551 or T552 is faulty or it is not getting correct bias).

5. Turn Off the instrument. 6. Check resistance between emitter and base of T552 using multi-meter. If it

shows zero or very low value then, base and emitter are getting shorted. 7. Remove the shorting shunt from pin 1 and 2 or jumper J6 and place it on pin 2

and 3.

8. Turn On the instrument and check the Y position functioning, it should work.

Results : Due to short circuit or damaged base emitter of transistor T552 the Y position shift was not possible. Fault 7 : CH I Y-shift is not correct, but CH II is correct.

Symptoms : When Y Pos I is moved trace does not move up and down.

Oscilloscope Settings : Scope is in CH I, mode and Y Pos moved up and down.

Fault Section : Chopper circuit.

ST2001E


Procedure : 1. Turn On instrument.

2. Keep instrument in CH I mode. 3. Check voltage at TP13, if not then, instead of 8 VDC, we get 24 VDC,

4. Check voltage at base of T252, it should be 10V, if not, instead of 10 V we get 24V, (If the voltage at base of T252 is correct, but at TP13 is not, then either T252 is faulty or it is not getting connected to power supply.)


6. Check the resistance between base and collector of T252, if it shows zero Ω, then it shows that the base and collector are either shorted or damaged.

7. Remove the shorting shunt from pin 1 and 2 of jumper J7, and place it on pin 2 and 3.

8. Turn On the instrument, now Y shift should work in both up and down directions.

Results : Due to short circuit between base and collector of T252 Y position of CH I was not working.

Fault 8 : No chop operation in Dual-Chop mode. Symptoms : In Dual Alternate mode the both traces comes one after

each other, but when Dual-Chop is selected only one of the trace is visible.

Oscilloscope Settings : Scope is in Dual-Chop mode. Fault Section : Chopper circuit.

Procedure : 1. Turn On the instrument.

2. Check the waveform at TP13 and TP12, it should be same given on this manual in Dual Chop mode, if not then,

3. Check wave at pin 13 and pin 12 of IC4013, it should be 12 Vpp, if not then,

4. Check the waveform at pin 11 of IC 251, 4013, it should be 12 Vpp, if not then,

5. Check the waveform at collector of T253, BC237, it should be 5 Vpp, if not then,

6. If the waveform at the collector of T253 is not correct, then either T253 is faulty or it is not getting proper bias voltage.

ST2001E


7. Turn Off the instrument, check transistor T253 , BC237 , if the emitter base shows zero resistance or very low resistance , then the transistor base emitter has damaged.

8. Remove the shorting shunt from the pin 1 and 2, and place it on 2 and 3 of jumper J8.

9. Turn On the instrument and check the Dual-Chop function, it should work. Results : Due shorting between base and emitter of transistor T253 chop frequency astable multi-vibrator was not working. Fault 9 : No alternate operation in Dual-Alt mode. Oscilloscope Settings : Dual-Alt mode, set time base switch to 50 µs/Div Fault Section : Chopper circuit. Symptoms : In Dual-Alt mode CH I trace is visible, but CH II is not Procedure : 1. Turn ON the instrument. 2. Check the waveform at TP12 and TP13 , if not then, 3. Check the waveform at pin 12 and 13 of IC251, IC 4013, it should be 12Vpp, if

not then, (If the waveform at pin 12 and 13 is not correct , but at TP12 and TP13 it is not correct, then the transistor T251 or T252 is faulty, or they are not getting +24 V power supply).

4. Check the power supply voltage of IC251, 4013, pin 7 should be at -12 V and pin 14 at 0V.

5. Check the waveform at pin 11 of IC251 IC4013 , it should be .12 Vpp, if not then,

6. Check the waveform at collector of transistor T254 , BC557 , it should be 12V pp, if not then,

7. Check the waveform at base of T254, BC557, it should be 12Vpp, if not then, (If the waveform at base of T254 is correct , but at collector it is not correct , then the transistor T254 may not getting power supply or the transistor is faulty).

8. Check the waveform at TP31 blue color, alternate pulse it should 3.5 V pp, if not then, 9. Check waveform at TP31 red color in Timebase circuit. 10. If the waveform at TP31 (red) is correct, but at TP31 (blue), it is not correct, them the track between them may be open.

9. Turn Off the instrument. Remove shorting shunt from 1 and 2 of jumper J9, and place it on pin 2 and 3.

10. Turn On the instrument. 13. Check the waveform at TP12 and TP13, Dual mode, Alternate should now work properly.

ST2001E


Results : Due to open circuit between TP31 (red) and TP31 (blue) alternate pulse was not reaching at T254. By placing jumper shorting shunt, two points got connected. Fault 10 : No trigger from internal source. Symptoms : Fast moving or unstable display of signal applied. Oscilloscope Settings : Connect sine wave signal, of 1Vpp at 5 KHz, to either

input at CH I or CH II, set the attenuator to 0.2 V/Div and input coupling to AC.

Fault Section : Trigger circuit. Procedure : 1. Turn On the instrument. 2. Check the waveform at TP30, it should be 4 V pp if not then, 3. Check the waveform at TP23 and TP29, it should be same as waveform shown

in Test point details on page 7, if not then, (If the waveform at TP28 and TP29 is correct, but at TP30, it is not correct then either IC401, IC529 is faulty or it is not getting proper supply voltages).

4. Check the waveform at R004 , 470R ,it should be 3.0 Vpp, if not then, 5. Check the waveform at TPI5 , Red colour in trigger amplifier, it should be

3.0V pp, if not then,

6. Check at TP15, Blue colour, it should be 3.0 Vpp, if not then, 7. Check DC voltage at TP15 (red) and TPI5 (blue). 8. If the waveform at TP15 (Blue) is different from, but at TP15 (Red), then track

is open between the two. 9. Turn Off the instrument. Remove the shorting shunt from 1 and 2 of jumper J10

and place it on pin 2 and 3. 10. Turn On the instrument, now the signal should be triggered. Results : Due to open circuit, the signal was unable to reach to the trigger circuit, by making the connections, signal got triggered. Fault 11 : Time Base dead Symptoms : No trace, or signal displayed on the screen at any time

base speed. But speed is visible on left most point. Keep the

intensity to lowest to avoid CRT phosphors burning. Oscilloscope Settings : Set all push buttons out, and all potentiometer controls

in the centre. Fault Section : Time base circuit.

ST2001E


Procedure : 1. Turn on the instrument. 2. Check the waveform at TP34, it should be a sawtooth, if not then, 3. 3. Check +24 V power supply at common end of R431……..R436. 4. Check the voltage at pin 14 of IC 402; it should be +5 V. 5. Check the waveform at pin 6 of IC 402, 74LS74, it should be pulse train, if not

then, 6. Check the voltage at R420, 51R, it should be similar to the voltage at pin 6. 7. If the voltage at pin 6 is not same, then the track between the two is open. 8. Turn Off the instrument, remove the shorting shunt from pin 2 and 3 of jumper

J11 and place it on 1 and 2 9. Turn On the instrument, now check the Timebase display on the screen, i.e. the

trace now should be visible. Results : Due to open circuit between R420 and the pin 6 of IC 402, the IC was not in function. Hence the Timebase was not generated.

Fault 12 : No timebase on speeds 0.5 µs/cm 50µs/cm and 5 ms/cm Symptoms : The timebase at this speed is not visible and hence the

signal is also not displayed, a spot will be visible, keep the intensity to lowest, to avoid the burning of CRT phosphor.

Oscilloscope Settings : All pushbuttons out, all potentiometer controls in the centre.

Fault Section : Time base circuit.

ST2001E


Procedure : 1. Turn On the instrument. 2. Keep the time base switch at 50 µs/cm position. 3. Check voltage at emitter of T405 , BC557 , it should be 24 V , if not then, 4. Check voltage at R431, 10K, at the end, which is connected to the timebase

wafer. It should be 24 V, if not then, (If the voltage at R431 is correct, but at emitter it is not, it means that the time base switch wafer is faulty).

5. Check voltage at R431, end common to R432……R436, it should be +24 V, if not then,

6. Check voltage at R432, end common to R431 R436, it should be + 24 V. 7. If the voltage is correct at R432, but not at R431, then the track between two is

open. 8. Turn Off the instrument, remove the shorting shunt form pin 1 and 2 of jumper

J12 and place it on 2 and 3. 9. Turn On the instrument, the trace at all these three speeds should be visible.

Results : Due to open track the constant current source resistors at these speed was not connected and, thus the constant current was not available for charging the timing capacitors.

Fault 13 : No CT, only spot appears on the screen Symptoms : Timebase is working, but a spot appears when CT is

selected. Oscilloscope Settings : Press the pushbutton CT and keep all other pushbuttons

out, set all potentiometer controls in the centre. Fault Section : Component Tester circuit.

ST2001E


Procedure : 1. Turn On the instrument select the CT mode. 2. Check the voltage at CT input terminals, it should be approximately 8 Vrms, if

not then, 3. Check the voltage at base of T406 or TP405 in timebase, it should sine 2.6

Vrms , if not then 4. Check the voltage at TP08, if not then, 5. Check the voltage at R9, end common to R10 in component tester circuit, it

should be 2.6 Vrms sine, if not then, (If the voltage at R9 is correct, but at base of T406 is not correct, then CT switch may be faulty).

6. Check voltage across at TP63 and TP62 in component tester circuit, it should be 8.6Vrms sine, if not then,

7. Check voltage at secondary of transformer, it should be 8.6 Vrms sinewave. 8. If voltage is correct, then track between the two is open. 9. Turn Off the instrument. 10. Remove shorting shunt from 2 and 3 of jumper J13, and place it on pin 1 and 2. 11. Turn On the instrument and check the CT operation. Results : Due to open circuit CT circuit was not getting 8.6 Vrms and CT was not working. Fault 14 : No trace but, time base is present.

Oscilloscope Settings : Time base at 50µs/cm all push buttons out all potentiometers in the centre

Fault Section : x - Final amplifier Symptoms : Sawtooth is generated, but no trace is visible, no CT

works.

ST2001E


Procedure : 1. Turn On the instrument. 2. Check the voltage at R504, it should be-2 V to +6 V, by varying the X Pos

potentiometer, if not then, 3. Check the variation at TP37, it should be 0 to 9 V. 4. If the voltage at TP37 is correct, but at R504 it is not, then T505 is faulty. 5. Turn Off the instrument, check the resistance between base and emitter of T505,

if it shows zero, then base and emitter are getting shorted. 6. Remove the shorting shunt from pin 1 and 2 of jumper J14 and place it on pin 2

and 3. 7. Turn On the instrument, and check the trace, it should be visible and should

move left and right by moving X Pos control. Results : Due to short circuit at base and emitter of transistor T505, the biasing of forward transistor was disturbed, and hence the time base was actually single sided. Fault 15 : Limited, X position, one sided trace Symptoms : Trace is on only one side and X-position potentiometer

is not working properly.

Oscilloscope Settings : Timebase at 50 µs/cm all push buttons out, all potentiometers in the centre

Fault Section : X-Final amplifier. Procedure : 1. Turn On the instrument. 2. Check the voltage at TP37, if not then, 3. Check the voltage at R517, 12 K end common to potentiometer P501, 10 K, it

should be 9V, if not then, (If the voltage at R51 7 is correct, but at TP37 it is not, then P501 may be faulty).

4. Check the voltage at R517 , end common to R518 , it should be +24 V, if not then,

5. Check the voltage at R518 , it should be +24 V, if not then, 6. If the voltage at R518 is correct, but at R517 it is not, then track between the

two is open. 7. Turn Off the instrument, remove the shorting shunt from pin 2 and 3 of jumper

J15 and place it on pin 1 and 2. 8. Turn On the instrument and check the X Pos control, it should work. Results : Due to opening between the R517 and R518, X positioning was not working

ST2001E


Actual Shorting Shunt Position on Jumpers

ST2001E


Warranty

1. We guarantee the product against all manufacturing defects for 36 months from the date of sale by us or through our dealers. Consumables like dry cell etc. are not covered under warranty.

2. The guarantee will become void, if

a) The product is not operated as per the instruction given in the operating manual.

b) The agreed payment terms and other conditions of sale are not followed. c) The customer resells the instrument to another party.

d) Any attempt is made to service and modify the instrument. 3. The non-working of the product is to be communicated to us immediately giving

full details of the complaints and defects noticed specifically mentioning the type, serial number of the product and date of purchase etc.

4. The repair work will be carried out, provided the product is dispatched securely packed and insured. The transportation charges shall be borne by the customer.

List of Accessories

1. BNC to Crocodile Cable ........................................................................ 1 No.

2. BNC to Test Prod Cable......................................................................... 1 No.

3. Test Probe Set........................................................................................ 1 No. 4. Mains Cord ............................................................................................ 1 No.

5. e-manual ................................................................................................ 1 No. Updated 26-07-2008

cro manual

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