Trouble
Remedy
Probable Cause
Purge the fuel system. Refer to
Fuel not
f.
Entrapped air in
6.
reaching
the fuel system.
purging procedure is applicable.
APU. (Cont)
Battery volt-
Weak or dead cells.
Recharge or replace the battery.
7.
age low.
Inlet or ex-
Loose screening or in-
Repair screening or insulation as
8.
sulation,
necessary.
haust
silencer
noisy.
Control
9.
Malfunctions of the APU are not
Console
fully discussed in this manual.
When APU troubles occur, follow
the troubleshooting instructions out-
lined in TM 55-1520-209-20 to iso-
late the cause. Troubles traced to
the control console must be located
by a continuity check to find the de-
fective component. Refer to para-
graphs 6-3 through 6-14 for control
system malfunction information.
See figures 6-2 and 6-3 for continu-
ity checks.
Figure 6-1. Table of Troubleshooting Procedures (Sheet 5 of 5)
G-3. TROUBLESHOOTING ELECTRICAL CONTROLS.
6-4. Malfunctions in the APU controls should be traced only after it has been estab-
lished that the battery is in good condition and that all electrical connections are cor-
rectly and tightly connected. It is recommended that APU electrical components be
checked for proper operation before troubleshooting the check stand control compo-
nents.
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
in the console comprise the power supply to the APU.
6-5
