Failure of the Standby Horizon Indicator

TASK 34-22-00-810-802-A
Failure of the Standby Horizon Indicator

1. Possible Causes

IND-STANDBY HORIZON [7FN]
wiring of the 28VDC signal from the circuit breaker (5FN) to the standby horizon indicator (7FN)
wiring of the ground signal at the standby horizon indicator (7FN)
C/B-NAV/STBY/HORIZON [5FN]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
ASM 342201
AMM 34-22-24-000-001	Removal of the Standby Horizon Indicator
AMM 34-22-24-400-001	Installation of the Standby Horizon Indicator

3. Fault Confirmation
Subtask 34-22-00-865-050-A ** ON A/C NOT FOR ALL

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

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C NOT FOR ALL
49VU	NAV/STBY/HORIZON	5FN	F12

Subtask 34-22-00-710-051-A ** ON A/C NOT FOR ALL

B. Test
(1) Not applicable, the fault is evident.
(a) If the circuit breaker (5FN) trips, refer to Para. 4.B. of this trouble shooting procedure.

4. Fault Isolation
Subtask 34-22-00-810-051-A ** ON A/C NOT FOR ALL

A. If the circuit breaker (5FN) is closed and if the flag is shown on the standby horizon indicator:

(1) If there is 28VDC:

(2) If there is no 28VDC:

do a check of the wiring of the 28VDC signal from the circuit breaker (5FN) to the standby horizon indicator (7FN)
do a check of the wiring of the ground signal at the standby horizon indicator (7FN), pin A/B
ASM 342201.

(a) If there is no continuity:

(b) If there is continuity:

Subtask 34-22-00-810-052-A ** ON A/C NOT FOR ALL

B. If the circuit breaker (5FN) is open and if the flag is shown on the standby horizon indicator:

(1) If the circuit breaker (5FN) trips:

(a) If the fault continues:

do a check for a short to ground from the circuit breaker (5FN) to the standby horizon indicator (7FN) ASM 342201.

1 If there is a short to ground:

2 If there is no short to ground:

Subtask 34-22-00-710-052-A ** ON A/C NOT FOR ALL

C. Make sure that the flag is out of view.

[Rev.8 from Aug 2018] 2026.04.04 04:32:55 UTC