technical information document only for the sinclair ...2... · the impedance of r9 (470 ),...

TECHNICAL INFORMATION DOCUMENT Only For The Sinclair Spectrum +2 (Grey Model) RGB Scart, Blanking Signal Mod - 21/09/2019 v1.0 Written By Ian Priddey - [email protected] This Modification will usually cure a flickering (Picture sync issue), ghosting or very dark picture, when using an RGB Scart Lead with some LCD TV’s, by disconnecting the Composite video signal on pin 1 of the Spectrums video socket, and replacing it with +12V, which with attenuation, provides the correct blanking signal voltage on pin 16, of the Scart plug, thus switching the TV into RGB mode. This is basically changing the video out link settings, from Standard to Péritel mode. 1. Open the Spectrum case, taking care not to damage the keyboard ribbon cable. Remove the keyboard, Heatsink, voltage regulator, and circuit board. 2. board, remove LINK 4 (LK4) and fit into LINK 2 (LK2) position. Replace R9 (1KΩ) resistor, with a 470Ω 1/4 watt resistor. Issue 1 3. board Remove LK4, and fit into LK2 position. Fit a 470Ω 1/4 watt resistor (R9). Issue 3 The resistance of R9 (470Ω), combined with the 75Ω input impedance of the blanking signal on pin 16 of the Scart plug, forms a voltage divider circuit, which will supply a voltage of about 1.5v DC on pin 16 of the Scart plug (when plugged into the TV), which will now switch the TV into RGB mode, and should fix all the issues mentioned above. Without this mod the Spectrum +2, uses the Composite video signal to supply the blanking signal voltage, and on some TV’s this won’t be suitable to switch the TV into RGB mode, so will switch to Composite video (CVBS) mode instead, and display the symptoms above. Blanking signal Specs - CVBS (Composite Video) mode 0-0.4V RGB mode 1-3V. ONLY CARRY OUT THIS MOD IF YOU ARE SUITABLY EXPERIENCED IN BASIC SOLDERING AND ELECTRONICS REPAIR MODIFIED R44 Website: ebay Shop: www.RetroComputerShack.com http://stores.ebay.co.uk/Retro-Computer-Shack ISSUE 3 BOARD MOD ISSUE 1 BOARD MOD R9 AND LINKS ARE ALL SITUATED JUST BELOW THE RGB VIDEO CONNECTOR LINK 4 REMOVED LINK 4 REMOVED LINK 2 FITTED LINK 2 FITTED R9 FITTED 470Ω ¹⁄ W R9 REPLACED WITH A 470Ω RESISTOR RetroComputerShack QUALITY RETRO COMPUTER PRODUCTS

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Page 1: TECHNICAL INFORMATION DOCUMENT Only For The Sinclair ...2... · The impedance of R9 (470 ), combined with the 75 input impedance of the blanking signal on pin 16 of the Scart plug,

TECHNICAL INFORMATION DOCUMENTOnly For The Sinclair Spectrum +2 (Grey Model)

RGB Scart, Blanking Signal Mod - 21/09/2019v1.0Written By Ian Priddey - [email protected]

This Modification will usually cure a flickering (Picture sync issue), ghosting or very dark picture, when using an RGB Scart Lead with some LCD TV’s, by disconnecting the Composite video signal on pin 1 of the Spectrums video socket, and replacing it with +12V, which with attenuation, provides the correct blanking signal voltage on pin 16, of the Scart plug, thus switching the TV into RGB mode.This is basically changing the video out link settings, from Standard to Péritel mode.

1. Open the Spectrum case, taking care not to damage the keyboard ribbon cable. Remove the keyboard, Heatsink, voltage regulator, and circuit board.2. board, remove LINK 4 (LK4) and fit into LINK 2 (LK2) position. Replace R9 (1KΩ) resistor, with a 470Ω 1/4 watt resistor. Issue 13. board Remove LK4, and fit into LK2 position. Fit a 470Ω 1/4 watt resistor (R9). Issue 3

The resistance of R9 (470Ω), combined with the 75Ω input impedance of the blanking signal on pin 16 of the Scart plug, forms a voltage divider circuit, which will supply a voltage of about 1.5v DC on pin 16 of the Scart plug (when plugged into the TV), which will now switch the TV into RGB mode, and should fix all the issues mentioned above. Without this mod the Spectrum +2, uses the Composite video signal to supply the blanking signal voltage, and on some TV’s this won’t be suitable to switch the TV into RGB mode, so will switch to Composite video (CVBS) mode instead, and display the symptoms above. Blanking signal Specs - CVBS (Composite Video) mode 0-0.4V RGB mode 1-3V.

ONLY CARRY OUT THIS MOD IF YOU ARE SUITABLY EXPERIENCED IN BASIC SOLDERING AND ELECTRONICS REPAIR

MODIFIED R44

Website: ebay Shop: www.RetroComputerShack.com http://stores.ebay.co.uk/Retro-Computer-Shack

ISSUE 3 BOARD MODISSUE 1 BOARD MOD

R9 AND LINKS ARE ALL SITUATED JUST BELOW THE RGB VIDEO CONNECTORLINK 4REMOVED

LINK 4REMOVED LINK 2

FITTED

LINK 2FITTED

R9 FITTED470Ω ¹⁄ W

R9 REPLACEDWITH A 470Ω RESISTOR

RetroComputerShackRetroComputerShackQUALITY RETRO COMPUTER PRODUCTSQUALITY RETRO COMPUTER PRODUCTS

Fine Blanking