airscan alternator t-shooting test box

AirScan Alternator System Diagnostic Test Box

AirScan C337 Alternator System Diagnostic Test Box

AirScan C337 Alternator System Diagnostic Test Box Training Session Overview

Classroom 45 Minutes IntroductionTroubleshooting 101Test Box Basic review of the C337 Alternator SystemFault IsolationHelpful TipsReview and Questions

Hands on 20 MinutesTest Box connectionTest Box operation

AirScan C337 Alternator System Diagnostic Test Box INTRODUCTION

Cessna 337 Alternator System


Cessna 337 Alternator System High rate of failure


Cessna 337 Alternator System High rate of failureOperational impact of failures


Cessna 337 Alternator System High rate of failureOperational impact of failuresSignificant amount of repeat write-ups


Cessna 337 Alternator System High rate of failureOperational impact of failuresSignificant amount of repeat write-upsNo standard troubleshooting process


Cessna 337 Alternator System High rate of failureOperational impact of failuresSignificant amount of repeat write-upsNo standard troubleshooting processTime and cost saving opportunity


The intent of this training is to provide the Technician with the basic knowledge and tools to enable efficient troubleshooting of the alternator system of the Cessna 337 legacy models. It is not applicable to the Raven 550s.

AirScan C337 Alternator System Diagnostic Test Box TROUBLESHOOTING 101

Every aviation maintenance organization is responsible for performing the full range of maintenance tasks. However, these tasks do not count equally in determining whether or not an organization is doing a good job.

The basis for judging the efficiency and effectiveness of a maintenance organization, and of individual maintenance workers, is the ability to find and fix problems efficiently. Quote: Michael E. Maddox - ERAU


Research related to troubleshooting has greatly increased our understanding of factors affecting performance. An extensive analysis of previous research published in the mid-1980's identified three general skills that appear to produce good troubleshooting performance:

Ability to repair or replace system components Ability to make tests to eliminate components from further consideration Ability to employ a strategy to search for failed components.

Most researchers focus on the ability to employ an efficient strategy as the most important and the most difficult to teach and learn.


Inefficient Troubleshooting - Improper diagnoses cause inefficiency in the maintenance process. However, improper diagnoses are not as potentially degrading to efficiency as inefficient troubleshooting strategies. AMTs tend to apply the same strategies to nearly every problem they address. Thus, an inefficient strategy's effects are multiplied across every troubleshooting task a maintainer performs.


Easter Egging (Shot Gunning)

One method of troubleshooting is to replace various LRUs until the symptoms of trouble disappear. This method is known as "Easter Egging" because a technician never really knows where he or she will find the failed part.

Easter Egging is an extremely inefficient, expensive way to find a problem.


Troubleshooting errors are the bane of most aviation maintenance organizations. In fact, troubleshooting is notoriously error-prone. The fundamental complexity of many aircraft systems contributes to the number and type of errors observed in actual troubleshooting tasks. Various strategies can be used to reduce troubleshooting errors - The structure imposed on troubleshooting activities varies widely among organizations. In some cases, maintenance personnel are allowed to develop their own diagnostic strategies.

In others, diagnostic procedures are tightly controlled by procedures or step-by-step job aids. Even within the same maintenance organization, the flexibility of troubleshooting strategies may vary considerably.


A number of research studies consistently have shown that proceduralization improves most measures of troubleshooting performance.

Two aspects of proceduralization are most salient for aviation maintenance:

First, when procedures are simple and apply to the specific system on which work is being performed, they lead to the most pronounced improvements.

Second, proceduralization can reduce, can in fact eliminate, differences in troubleshooting performance between experts and novices.


The alternator system troubleshooting procedures that follows are a form of proceduralization .

The goal is to timely and accurately isolate and rectify alternator system malfunctions on the Cessna 337.

AirScan C337 Alternator System Diagnostic Test Box ALTERNATOR SYSTEM DIAGNOSTIC TEST BOX Test Indicator Lights Voltmeter Test Jacks Isolation Diode Test Switch Full Charge Simulation Switch Volt/Amp Display Display Power Switch

Test Mode Rotary Switch

AirScan C337 Alternator System Diagnostic Test BoxALTERNATOR SYSTEM DIAGNOSTIC TEST BOX CONNECTIONS


Ground clip to suitable ground point.

Molex connectors patch into Voltage Regulator.


Alligator clip connectionsfrom 2 prong connector on box

Black to top of diode.

Red to bottom of diode.


Alligator clip connectionsfrom multi-pin connector on box to ammeter shunt.

Red to power-in post.

Black to bus bar side of shunt.

AirScan C337 Alternator System Diagnostic Test Box Basic Review of the C337 Alternator System

AirScan C337 Alternator System Diagnostic Test Box Fault IsolationTest Box

TP1 TP2 TP3 TP4

Normal Indication

Display=TP1 - 0 VTP2 - 0 VTP3 - 4-6 V ResidualTP4 - Battery Voltage


TP1 TP2 TP3 TP4

No Light on TP4

Display=TP1 - 0 VTP2 - 0 VTP3 - 0 VTP4 - 0 V

Primary wiring defect between battery and isolation diode.


TP1 TP2 TP3 TP4

Normal operation

Display=TP1 - Battery VoltageTP2 - Within 1-2V of TP1 TP3 - 4-6 V ResidualTP4 - Battery Voltage

AirScan C337 Alternator System Diagnostic Test Box Fault Isolation Test Box

TP1 TP2 TP3 TP4

No TP1 or TP2 Light

Display=TP1 - 0VTP2 - 0V TP3 - 4-6 V ResidualTP4 - Battery Voltage

Field or Start CB poppedFuse on Diode Assembly openOver Voltage Sensor failureAlternator Switch failureWiring problem


TP1 TP2 TP3 TP4

No TP2 Light

Display=TP1 - Battery VoltageTP2 - 0V TP3 - 4-6 V ResidualTP4 - Battery Voltage

AirScan C337 Alternator System Diagnostic Test Box Fault IsolationTP1 TP2 TP3 TP4

Battery Master SW On, Alternator SW On, Engine Off

No TP2 Light

Select rotary test switch to Field Current.

Normal field current will be 2-4 Amps.

If full scale (5 Amps) this indicates shorted alternator field or short in field wire between regulator and alternator.

Zero or very low amps on display indicates a malfunctioning Voltage Regulator.


TP1 TP2 TP3 TP4

Normal Operation

Display= *TP1 - 27.5 +- .2 VTP2 - Variable TP3 - 28.5 +- 2.5 VTP4 - 27.5 +- .2 V

*Battery stabilized. 1000 RPM. Landing and taxi lights ON.


TP1 TP2 TP3 TP4

No TP3 Light

Display= TP1 - Battery VoltageTP2 - Within 1-2V of TP1 TP3 - 4-6 V ResidualTP4 Battery Voltage


Battery Master SW On, Alternator SW On, Engine On

No TP3 Light

Select rotary test switch to Field Current.

Normal field current will be 2-4 Amps with a load on the system. Maybe less than an amp if no load and battery charged. If field current is normal then Alternator itself or Alternator Drive Coupling has failed.

If field current is not in the normal range then inspect field wire and connections between Voltage Regulator and Alternator for defects.


TP1 TP2 TP3 TP4

All lights on but Alternator Fail Light lit.

Display= *TP1 - 27.5 +- .2 VTP2 - Variable TP3 - 28.5 +- 2.5 VTP4 -


Battery Master SW On, Alternator SW On, Engine On

All Lights On but Alternator Fail Light Lit

Select rotary test switch to Alternator Current.

If no charge current indicated then:

Momentarily move Isolation Diode switch to Parallel. If normal current is observed replace open diode.

AirScan C337 Alternator System Diagnostic Test Box Helpful TipsTP1 TP2 TP3 TP4

Aircraft with Dual Volt/Amp meters:

The Cessna 337 alternator system downstream of the isolation diodes is a single bus.

The shunts for the Dual Volt/Amp meters are downstream of the isolation diodes.

Therefore, the amp readings are not an accurate indication of what load each alternator is picking up.

Primary indication of an alternator problem is the aircrafts respective Alt Fail light.


Intermittent Failures

Blinking Alt Fail LightVoltage Regulator settingsWith pulsing post lightsPossible Diode Board Assembly

Solid on and off intermittent LightAlternator SwitchWith low field input voltage to regulatorFaulty Over Voltage Sensor or associated connections


System Operation

Best Practices It has been proven to help negate alternator failures by allowing battery to recharge following engine start before bringing avionics, sensor station power and especially MCU power on line.Usually, three to four minutes is all that is needed with both alternators up and running.

AirScan C337 Alternator System Diagnostic Test Box ReviewTP1 TP2 TP3 TP4

Questions?

airscan alternator t-shooting test box

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