Loss of the BUS 4 Data from the CFDIU to the VHF 3

TASK 23-12-00-810-821-A
Loss of the BUS 4 Data from the CFDIU to the VHF 3

1. Possible Causes

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 23-12-00-740-001	BITE Test of the VHF System
AMM 23-12-33-000-001	Removal of the VHF Transceiver
AMM 23-12-33-400-001	Installation of the VHF Transceiver
ASM 313205

3. Fault Confirmation
Subtask 23-12-00-865-055-A

A. Make sure that this(these) circuit breaker(s) is(are) closed:

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C ALL
121VU	CFDS/CFDIU/SPLY	2TW	J18
121VU	CFDS/CFDIU/BACK/UP	8TW	J17

Subtask 23-12-00-740-072-A

B. Test
Do the BITE test of the VHF system AMM 23-12-00-740-001.

NOTE: Do this test for the VHF 3 only.

4. Fault Isolation
Subtask 23-12-00-810-076-C

A. If the test gives the maintenance message CFDIU (1TW)/VHF3 (1RC3):

(1) If the fault continues:

do a check and repair the wiring of the BUS 4 OUTPUT signal, (from VHF 3 transceiver (1RC3) pins AB/6A, 6B to the first terminal block) ASM 313205.

Subtask 23-12-00-740-073-A

B. Do the test given in Para. 3.B.

[Rev.8 from Aug 2018] 2026.04.04 04:25:38 UTC