TROUBLESHOOTING ELECTRICAL CONTROLS. - TM-55-4920-424-13-P0168

TM 55-4920-424-13&P

Trouble

Probable Cause

Remedy

Control

Malfunctions of the APU

Console.

fully discussed in this Appendix.

When APU troubles occur, follow

the trouble shooting instructions

outlined in appropriate TM to isolate the

cause. Troubles traced to the

control console must be

located by a continuity check

to find the defective

component. Refer to paragraphs

6-3 through 6-6 for control

system malfunction information. Refer

to drawings in this Appendix for

Figure E-18. Table of Troubleshooting Procedures (Sheet 2 of 2)

6-3.

TROUBLESHOOTING ELECTRICAL CONTROLS.

6-4.

Malfunctions in the APU controls should be traced only after it has been established that the battery is in good

condition and that all electrical connections are correctly and tightly connected. It is recommended that APU electrical

components be checked for proper operation before troubleshooting the check stand control components.

6-5.

Before performing any troubleshooting procedures, always verify that the power supply components to the APU

controls are functioning properly, furnishing 24-volt dc power to the control circuits, and are charging the battery. The

following components comprise the power supply to the APU.

Battery

DC starter-generator

Circuit br eaker CB1

DC voltage regulator VRI

Circuit breaker CB2

Reverse current cutout

Starter dropout relay

6-6.

If fuel supply problems are encountered, check switch S3, K3 and then check the boost pump for proper

operation.

E-52 Change 2