28V Failure

TASK 38-31-00-810-845-A
28V Failure

1. Possible Causes

AIRCRAFT WIRING
DEU-B [300RH8]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 23-73-47-000-001	Removal of the Decoder/Encoder Unit B (300RH)
AMM 23-73-47-400-001	Installation of the Decoder/Encoder Unit B (300RH)
AMM 38-31-00-710-009	Operational Test of the Toilet Unit
AMM 38-31-00-740-001	BITE Test of the Vacuum Toilet System
ASM 383110
MCDU Display

3. Fault Confirmation
Subtask 38-31-00-710-137-A ** ON A/C NOT FOR ALL

A. Do a test of the vacuum toilet system AMM 38-31-00-710-009.

Subtask 38-31-00-740-080-A ** ON A/C NOT FOR ALL

B. Do the procedure to get access to the CFDS SYSTEM REPORT/TEST menu PAGE AMM 38-31-00-740-001.

4. Fault Isolation
Subtask 38-31-00-810-147-A ** ON A/C NOT FOR ALL

A. If the LAST/PREVIOUS LEGS Report gives the maintenance message
LLT (40MG) and LLS (41MG) and VACU GEN (37MG) SPLY
and
the FAP gives the maintenance messages
VACUUM SYSTEM DISABLED ON GROUND
and
NO WASTE QUANTITY DATA AVAILABLE:
(1) do a check of the AIRCRAFT WIRING for 28VDC at:

the liquid level transmitter pin B,
the liquid level sensor pin A,
the vacuum generator plug B pin A, C
the motor start relay pin G, H.

(a) If there is no 28VDC repair the aircraft wiring as necessary ASM 383110.
(2) If the fault continues:

replace the DEU-B [300RH8] , AMM 23-73-47-000-001 and AMM 23-73-47-400-001.

Subtask 38-31-00-710-138-A ** ON A/C NOT FOR ALL

B. Test
(1) Do the test as given in paragraph 3. A. to check the correct operation.
(2) After the subsequent flight, make sure that the fault does not continue.

[Rev.8 from Aug 2018] 2026.04.04 04:34:15 UTC