Failure of the BTC 1 Status Sense-Circuit

TASK 24-20-00-810-920-A
Failure of the BTC 1 Status Sense-Circuit

1. Possible Causes

GCU-1 [1XU1]
BTC-1 [11XU1]
wiring

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
ASM 242202
AMM 24-22-34-000-001	Removal of the GCU-1(2)
AMM 24-22-34-400-001	Installation of the GCU-1(2)
AMM 24-22-55-000-001	Removal of the Contactors
AMM 24-22-55-400-002	Installation of the Contactors
AMM 24-41-00-740-002	Operational Check of the GAPCU via the CFDS

3. Fault Confirmation
Subtask 24-20-00-740-082-A ** ON A/C NOT FOR ALL

A. Test
(1) Do the BITE test of the GAPCU AMM 24-41-00-740-002.

NOTE: If the CFDS message PB BUS TIE (10XU) / BTC1 (11XU1) / GCU1 (1XU1) comes into view when the flight crew or the maintenance personnel puts the BUS TIE pushbutton switch (10XU) in the released or OFF position the trouble shooting is not necessary. This can occur during an electrical system test or during trouble shooting.
If the flight crew or the maintenance personnel did not operate the BUS TIE pushbutton switch and this CFDS message comes into view, do the trouble shooting procedure that follows.

(a) If the BITE test gives the message TEST FAILED:

do the trouble shooting given in Para 4.A.

(b) If the BITE test gives the message TEST PASSED:

do the trouble shooting given in Para 4.B.

4. Fault Isolation
Subtask 24-20-00-810-183-A ** ON A/C NOT FOR ALL

A. If the BITE test gives the message TEST FAILED:

push the line key adjacent to the TEST FAILED message.

(1) If the maintenance message GCU1 (1XU1) comes into view:

replace the GCU-1 [1XU1] AMM 24-22-34-000-001 and AMM 24-22-34-400-001.

Subtask 24-20-00-810-172-A ** ON A/C NOT FOR ALL

B. If the BITE test gives the message TEST PASSED:

replace the BTC-1 [11XU1] AMM 24-22-55-000-001 and AMM 24-22-55-400-002.

(1) If the fault continues:

do a check of the status sense wiring for an open circuit or high resistance condition between pin A/4C of the GCU 1 and pin B/29 of the BTC 1 ASM 242202.

(a) If the wiring is not correct:

repair or replace as necessary.

(b) If the wiring is correct:

replace the GCU-1 [1XU1] AMM 24-22-34-000-001 and AMM 24-22-34-400-001.

Subtask 24-20-00-740-083-A ** ON A/C NOT FOR ALL

C. When you replace a component or repair the wiring:

do the subsequent flight before you do the check of the Class 3 Faults of the GAPCU from the CFDS to make sure that the system operates correctly.
If the test continues to give the fault message, continue the trouble shooting procedure.

[Rev.8 from Aug 2018] 2026.04.04 04:26:24 UTC