3)  If the ILS, GLS and GPS lights do not come on, on the IRS Mode Select Unit, when the RECALL annunciator on the IRS Master Caution Unit is pushed, then you corrected the fault.
4)  If the ILS, GLS and GPS lights come on, on the IRS Mode Select Unit, when the RECALL annunciator on the IRS Master Caution Unit is pushed, then continue.
(3)  If the ILS, GLS and GPS lights come on, on the IRS Mode Select Unit, when the RECALL annunciator on the IRS Master Caution Unit is pushed, then do these tasks: ILS
Light
On
When
Master
Caution
Pushed
-Fault
Isolation,
34-31
TASK
820

GLS
Light
On
When
Master
Caution
Pushed
-Fault
Isolation,
34-31
TASK
822

GPS
Light
On
When
Master
Caution
Pushed
-Fault
Isolation,
34-58
TASK
802

(a)  If the ILS, GLS and GPS lights do not come on, on the IRS Mode Select Unit, when the RECALL annunciator on the IRS Master Caution Unit is pushed, then you corrected the fault.
-------------------------END OF TASK ---------------------------
EFFECTIVITY SIL ALL  34-31 TASK 824 
D633A103-SIL BOEING PROPRIETARY -Copyright # Unpublished Work -See title page for details  Page 243 Jun 15/2010 

801.  Indications Normal, Audio Tone Problem -Fault Isolation
A.  Description
(1)  The audio tone does not occur or is weak when passing a marker, however indications are normal.
B.  Possible Causes
(1)
VOR/marker beacon receiver, M1724.

(2)  
Remote electronics unit, M1353.

(3)
Wiring.

C.  Circuit Breakers
(1)  This is the primary circuit breaker related to the fault:
CAPT Electrical System Panel, P18-1 Row Col Number Name A 1 C01374 RADIO NAVIGATION VOR/MKR BCN 1
D.  Related Data
(1)
(SSM 34-32-11).

(2)
(WDM 34-32-11).

E.  Initial Evaluation
(1) Do this task: Marker Beacon System -System Test, AMM TASK 34-32-00-730-801.
(a)  
If the audio tone do not occur or is weak, then do the Fault Isolation Procedure below.

(b)  
If the audio tone is normal, then there was an intermittent fault.

F. Fault Isolation Procedure
(1)  Do
this
task:
VOR/Marker
Beacon
Receiver
BITE
Procedure,
34-51
TASK
801.

(a)  If the VOR/marker beacon BITE test shows a fault, then go to the fault isolation task for the applicable maintenance message to correct the fault. 1) Do this task: Marker Beacon System -System Test, AMM TASK 34-32-00-730-801.
a) If the audio tone do not occur or is weak, then continue.
b) If the audio tone is normal, then you corrected the fault.
(b) If the VOR/marker beacon BITE test does not show a fault, then continue.

(2)  Do this check of the wiring:
(a)  
Remove the remote electronics unit, M1353. To remove it, do this task: Remote Electronics Unit (REU) Removal, AMM TASK 23-51-01-000-801.

(b)  
Remove the VOR/marker beacon receiver, M1724. To remove it, do this task: VOR/MKR Receiver Removal, AMM TASK 34-51-01-000-801.

(c)  
Do a continuity check between these pins of connector D3623B for the VOR/marker beacon receiver and connector D2501A for the remote electronics unit:

D3623B  D2501A
pinC4 ------------------pinA15 pinD4 ------------------pinA14

(d)  If there is not continuity, then do these steps: 1) Repair the wiring.
EFFECTIVITY SIL ALL  34-32 TASK 801 
D633A103-SIL BOEING PROPRIETARY -Copyright # Unpublished Work -See title page for details  Page 201 Jun 10/2006 
　
中國航空網 www.k6050.com
航空翻譯 www.aviation.cn
本文鏈接地址：737-600/700/800/900 FAULT ISOLATION MANUAL 故障隔離手冊 導航(115)