AirScan Alternator T-shooting Test Box

Training Session Overview
Classroom – 45 Minutes
• Introduction
• Troubleshooting 101
• Test Box
• Basic review of the C337 Alternator System
• Fault Isolation
• Helpful Tips
• Review and Questions
Hands on – 20 Minutes
• Test Box connection
• Test Box operation

AirScan C337 Alternator System Diagnostic Test Box
INTRODUCTION
Cessna 337 Alternator System –

INTRODUCTION
 High rate of failure

INTRODUCTION
 Operational impact of failures

INTRODUCTION
 Significant amount of repeat write-ups

INTRODUCTION
 No standard troubleshooting process

INTRODUCTION
 No standard troubleshooting process
 Time and cost saving opportunity

INTRODUCTION
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 550’s.

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

TROUBLESHOOTING 101
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.

TROUBLESHOOTING 101
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.

TROUBLESHOOTING 101
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 101
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.

TROUBLESHOOTING 101
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.

TROUBLESHOOTING 101
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.

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

ALTERNATOR SYSTEM DIAGNOSTIC TEST BOX CONNECTIONS

Ground clip to suitable
ground point.
Molex connectors patch
into Voltage Regulator.

Alligator clip connections
from 2 prong connector
on box –
Black to top of diode.
Red to bottom of diode.

Alligator clip connections
from multi-pin connector
on box to ammeter shunt.
Red to power-in post.
Black to bus bar side of
shunt.

Basic Review of the C337 Alternator System

Fault Isolation
Test Box
TP1 TP2 TP3 TP4
Normal Indication
Display=
TP1 - 0 V
TP2 - 0 V
TP3 - 4-6 V Residual
TP4 - Battery Voltage

Fault Isolation
Test Box
TP1 TP2 TP3 TP4
No Light on TP4
Display=
TP1 - 0 V
TP2 - 0 V
TP3 - 0 V
TP4 - 0 V
Primary wiring defect
between battery and
isolation diode.

Fault Isolation
Test Box
TP1 TP2 TP3 TP4
Normal operation
Display=
TP2 - Within 1-2V of TP1

Fault Isolation
Test Box
TP1 TP2 TP3 TP4
No TP1 or TP2 Light
Display=
TP1 - 0V
TP2 - 0V
Field or Start CB popped
Fuse on Diode Assembly open
Over Voltage Sensor failure
Alternator Switch failure
Wiring problem

Fault Isolation
Test Box
TP1 TP2 TP3 TP4
No TP2 Light
Display=
TP2 - 0V

Fault Isolation
TP1 TP2 TP3 TP4
Battery Master SW On, Alternator SW On, Engine Off
No TP2 Light
1. 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.

Fault Isolation
Test Box
TP1 TP2 TP3 TP4
Normal Operation
Display= *
TP1 - 27.5 +- .2 V
TP2 - Variable
TP3 - 28.5 +- 2.5 V
TP4 - 27.5 +- .2 V
*Battery stabilized.
1000 RPM.
Landing and taxi
lights ON.

Fault Isolation
Test Box
TP1 TP2 TP3 TP4
No TP3 Light
Display=
TP2 - Within 1-2V of TP1
TP4 – Battery Voltage

Fault Isolation
TP1 TP2 TP3 TP4
Battery Master SW On, Alternator SW On, Engine On
No TP3 Light
1. 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.

Fault Isolation
Test Box
TP1 TP2 TP3 TP4
All lights on but
Alternator Fail Light lit.
Display= *
TP1 - 27.5 +- .2 V
TP2 - Variable
TP3 - 28.5 +- 2.5 V
TP4 -

Fault Isolation
TP1 TP2 TP3 TP4
Battery Master SW On, Alternator SW On, Engine On
All Lights On but Alternator Fail Light Lit
1. 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.

Helpful Tips
TP1 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
aircraft’s respective “Alt Fail” light.

Helpful Tips
TP1 TP2 TP3 TP4
Intermittent Failures
 Blinking “Alt Fail” Light
 Voltage Regulator settings
 With pulsing post lights
 Possible Diode Board Assembly
 Solid on and off intermittent Light
 Alternator Switch
 With low field input voltage to regulator
 Faulty Over Voltage Sensor or associated
connections

Helpful Tips
TP1 TP2 TP3 TP4
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.

Review
TP1 TP2 TP3 TP4
Questions?

AirScan Alternator T-shooting Test Box

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