Should the same failure conditions be observed
c. The Air Data Subsystems Failure isolation
the Front Panel Assembly will be replaced in
Shop Set (FISS) provides slave boards for use
a c c o r d a n c e with Section V.
during troubleshooting to aid in the identification
of faulty circuit board assemblies within the EPU,
e. After the defective SRU has been replaced
once the faulty circuit board has been identified,
the EPU will be subjected to the functional tests
the slave board is returned to the shop set for
Iisted in Section Ill.
future use and a replacement board is requisi-
t i o n e d for the EPU.
d. When any EPU SRU is replaced in
accordance with Section V the step of the
troubleshooting procedure (Section IV) at which
the unit failed will be repeated prior to functional
testing. (Section Ill).
Table 5-10. Test Equipment for EPU Troubleshooting.
Tester, Pitot Static Systems
Shop Set, Failure Isolation,
Electronic Circuit Boards:
Air Data Subsystem
Table 5-11. Troubleshooting.
Test or Inspection
Fault Suspected In Electronics Processor Unit.
Step 1 Carry out the test set preliminary starting procedure as detailed in TM 9-4931-378-13&P, Chapter 2, Section II.
Step 2 Verify the test set performance by carrying out the test set operating procedure as detailed in TM
Step 3 Connect the EPU to the Test Set as shown in figure 5-8.
Step 4 Test the Test Set switches as follows:
S1 to CONT (UP)
S4 to DOWN
S7 to 30
S5 to DOWN
S2 to DOWN
B1 to 0°
S3 to DOWN
B2 to 0°
Switch on power to the EPU by operating CB1 and CB2.
Step 5 Using the Multimeter, measure the current at test points 13 (+ve) and 14 on the test set, ADS (LRU), with S12 set
to EPU 28V and S13 depressed. The result should be 1.4A ± 0.2A. Remove the Multimeter from TP13 and TP14.
If current is out of tolerance replace the Power Supply Unit as specified in Section V.