Loss of the ATSU/VHF3 Interface

TASK 23-12-00-810-826-A
Loss of the ATSU/VHF3 Interface

1. Possible Causes

XCVR-VHF, 3 [1RC3]
ATSU [1TX1]
wiring of the ATSU FREQ SELECT INPUT PORT A
wiring of the ATSU INPUT BUS COM-2

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 462106
AMM 46-21-34-000-001	Removal of the Air Traffic Service Unit (ATSU)
AMM 46-21-34-400-001	Installation of the Air Traffic Service Unit (ATSU)

3. Fault Confirmation
Subtask 23-12-00-740-074-A

A. Test
(1) 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 23-12-00-810-081-A

A. If the test gives the maintenance message :
ACARS MU1 (1RB1)/VHF3 (1RC3) or
RMP 1/2/3 (1RG1/2/3)/ACARS MU (1RB)/VHF 3 (1RC3)
(1) If the ACARS indication comes into view in the ACTIVE display window of the RMP where the VHF 3 is set:

replace the XCVR-VHF, 3 [1RC3] AMM 23-12-33-000-001 and AMM 23-12-33-400-001.

(a) If the fault continues:

replace the ATSU [1TX1] AMM 46-21-34-000-001 and AMM 46-21-34-400-001.

(b) If the fault continues:

remove the VHF 3 transceiver AMM 23-12-33-000-001
remove the ATSU AMM 46-21-34-000-001
check and repair the wiring of the ATSU FREQ SELECT INPUT PORT A between pins AA/1E, 1F of the ATSU and pins AB/11A, 11B of the VHF 3 transceiver ASM 462106.
check and repair the wiring of the ATSU INPUT BUS COM-2 between pins AB/1G, 1H of the ATSU and pins AB/12A, 12B of the VHF 3 transceiver ASM 462106.
install the ATSU AMM 46-21-34-400-001
install the VHF 3 transceiver AMM 23-12-33-400-001.

Subtask 23-12-00-740-075-A

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

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