Loss of Message Bus RS422 between the FWC 2 and the DMC 3

TASK 31-63-00-810-961-A
Loss of Message Bus RS422 between the FWC 2 and the DMC 3

1. Possible Causes

FWC-2 [1WW2]
DMC-3 [1WT3]
wiring from the FWC 2(1WW2) to the DMC 3(1WT3)

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
ASM 315205
AMM 31-53-34-000-001	Removal of the Flight Warning Computer (FWC)
AMM 31-53-34-400-001	Installation of the Flight Warning Computer (FWC)
AMM 31-60-00-740-002	Perform Electronic Instrument System (EIS) Input Test
AMM 31-60-00-740-007	GROUND SCANNING Test of the DMC
AMM 31-63-34-000-001	Removal of the DMC
AMM 31-63-34-400-001	Installation of the DMC

3. Fault Confirmation
Subtask 31-63-00-865-190-A

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

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C ALL
121VU	EIS/FWC2/SPLY	2WW	Q07

Subtask 31-63-00-740-332-A ** ON A/C NOT FOR ALL

B. Test
Do the EIS input test (system 1) AMM 31-60-00-740-002.

Subtask 31-63-00-740-332-B ** ON A/C NOT FOR ALL

B. Test
Do the Ground Scanning Test of the DMC AMM 31-60-00-740-007.

4. Fault Isolation
Subtask 31-63-00-810-209-A ** ON A/C NOT FOR ALL

A. If the test gives the maintenance message DMC3: NO FWC2 MSG:

replace the FWC-2 [1WW2] AMM 31-53-34-000-001 and AMM 31-53-34-400-001.

(1) If the fault continues:

replace the DMC-3 [1WT3] AMM 31-63-34-000-001 and AMM 31-63-34-400-001.

(a) If the fault continues:

do a check and repair the wiring from the FWC 2(1WW2) to the DMC 3(1WT3), pins AB/14J, 14K to pins AA/9G, 9H ASM 315205.

Subtask 31-63-00-810-209-B ** ON A/C NOT FOR ALL

A. If the test gives the maintenance message FWC2(1WW2) BUS MESSAGEX/DMC3(1WT3)

replace the FWC-2 [1WW2] AMM 31-53-34-000-001 and AMM 31-53-34-400-001.

(1) If the fault continues:

replace the DMC-3 [1WT3] AMM 31-63-34-000-001 and AMM 31-63-34-400-001.

(a) If the fault continues:

do a check and repair the wiring from the FWC 2(1WW2) to the DMC 3(1WT3), pins AB/14J, 14K to pins AD/5C, 5D ASM 315205.

Subtask 31-63-00-740-333-A

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

[Rev.8 from Aug 2018] 2026.04.04 04:30:49 UTC