CHAPTER 3 TROUBLESHOOTING

11-6625-667-45/NAVAIR

16-30APM123-2/T0

33A1-3-367-22

CHAPTER 3

TROUBLESHOOTING

Section I. GENERAL TROUBLESHOOTING TECHNIQUES

NOTE

inspection is to locate faults that may be evident

without testing or measuring. This includes

See Section I I I When Using

AN/TPM-25A.

broken wires, bent or corroded connector pins,

damage circuit boards, or loose rf jacks and

3-1. General Instructions

plugs. All possible visible inspections should be

Troubleshooting at general support and depot

performed before attempting operational tests.

(2) Sectionalization tests. The sec-

maintenance categories includes all techniques

outlined for organizational maintenance and any

tionalization tests are operational type tests and

frequently indicate the general location of

special or additional techniques required to

trouble. In some instances, the tests will help in

isolate a defective part. Section II of this chapter

determining the exact nature of the fault. Tests

provides intra-unit (within the unit localizing and

are given in paragraph 3-4.

isolating techniques to be used at the general

c. Localization. Localization procedures should

support maintenance category.

be performed after the trouble has been sec-

3-2. Organization of Troubleshooting

tionalized (b above. Localization procedures

Procedures

applicable to this equipment are described in

a. General. The first step in servicing a

paragraphs 3-5 and 3-6, and should be used in

localizing the trouble to a stage in the suspected

defective test set is to sectionalize the fault.

Sectionalization means tracing the fault to a

module or subassembly.

particular module or subassembly (for example,

d. Isolation Procedures for isolating troubles

encoder module A4 or transmitter A16). The

are given in paragraph 3-7.

second step is to localize the fault. Localization

e. Techniques. When performing the sec-

means tracing the fault to a defective stage or

tionalization para 3-4), localization, and isolation

circuit responsible for the abnormal condition.

procedures, one or more of the techniques

The third step is isolation. Isolation means

described below may be applied. Apply these

techniques only as indicated, and observe all

locating the defective part or parts.

b. Sectionalization The daily maintenance cautions.

checks and services (TM 11-6625-667-12).

(1) Voltage measurements. This equipment is

provides a satisfactory means of determining

transistorized. When measuring voltages, use

tape or sleeving (spaghetti) to insulate the entire

whether the transponder test set may be

test probe, except for the extreme tip. A

operating. Because of the nature of the self test

operation, the exact cause of an internal fault

momentary short circuit can ruin a transistor.

cannot be determined with this chart. The test set

Use the same or equivalent electronic multimeter

specified on the voltage and resistance diagrams.

provides only an accept or reject indication;

therefore, one or more internal circuits can cause

NOTE

an improper indication. To simplify the location

Modules A4, A5, and A7 through A12

of a fault, consider that there are four main

contain digital circuits. Do not attempt

functional s e c t i o n s i n T e s t S e t

to analyze their operation with voltage

TS-1890/APM-123(V). These functional sections

indications. Analyze their operation

include the power supply, transmitter, receiver,

with the waveforms shown in figures

and decoder. The first step in tracing trouble is to

8-17 through 8-23.

determine the module or subassembly of the

(2) Resistance measurements. Make resistan-

section that contains the fault.

(1) Visual inspection. The purpose of visual

Change 5 3-1