TROUBLESHOOTING ELECTRICAL CONTROLS. - TM-55-4920-424-13-P0073

TM 55-4920-424-13&P

Trouble

Probable Cause

Remedy

Control

Malfunctions of the APU are not

Console.

fully discussed in this manual.

When APU troubles occur, follow

the troubleshooting instructions

outlined in TM 55-2835-203-24 to

isolate the cause. Troubles traced

to the control console must be

located by a continuity check to find

the defective component. Refer to

control system malfunction infor-

mation. Refer to drawings in

enclosure for continuity checks.

Figure 6-1. Table of Troubleshooting Procedures (Sheet 5 of 5)

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

B contacts of relay K2

Circuit breaker CB1

Indicator light DS6

Circuit breaker CB2

DC starter-generator G#

Reverse current cutout K6

DC voltage regulator VR1

Starter dropout relay K7

Resistor R3

6-6. If fuel supply problems are encountered, first check switch S1, and then check the boost pump for proper operation.

6-7. If the fuel control system does not operate correctly, carefully check the function of each APU control component and

the corresponding relay contacts in the console.

6-5