(b)  
Remove the applicable LRRA receiver/transmitter. To remove it, do this task: Low Range Radio Altimeter (LRRA) Receiver/Transmitter (R/T) Removal, AMM TASK 34-33-21-000-801.

(c)  
Connect the TDR time domain reflectometer, COM-5187test set at pins 71 and C71 of the applicable connector at the LRRA receiver/transmitter (WDM 34-33-11, WDM 34-33-21).

(d)  
Do an electrical check of the coaxial cable and the antenna.

NOTE: The TDR test set has instructions which tell how to do the check of the cable and antenna.

(e)  
Disconnect the TDR test settime domain reflectometer, COM-5187.

(f)  
Re-install the LRRA receiver/transceiver. To install it, do this task: Low Range Radio Altimeter (LRRA) Receiver/Transmitter (R/T) Installation, AMM TASK 34-33-21-400-801.

(g)  
If you find a problem with the coaxial cable, then do these steps: 1) Replace the applicable coaxial cable (WDM 34-31-11). 2) Do
this
task:
Low
Range
Radio
Altimeter
(LRRA)
BITE
Procedure,
34-33
TASK
801.
3) If the red XMIT ANT FAIL light goes off, then you corrected the fault.

(h)  
If you find a problem with the antenna, do these steps:

LRRA 
LRRA-1 (M1735)  TDR TEST SET TDR TEST SET TDR --------------------TDR -------------------- CONNECTOR D3667B pin 71 pin C71 
LRRA-2 (M1736)  TDR TEST SET TDR --------------------TDR -------------------- D3669 pin 71 pin C71 

1) Replace the applicable LRRA antenna. These are the tasks: Low Range Radio Altimeter (LRRA) Antenna Removal, AMM
TASK 34-33-11-000-801,
Low Range Radio Altimeter (LRRA) Antenna Installation, AMM
TASK 34-33-11-400-801. 2) Do
this
task:
Low
Range
Radio
Altimeter
(LRRA)
BITE
Procedure,
34-33
TASK
801.
3) If the red XMIT ANT FAIL light goes off, then you corrected the fault.
-------------------------END OF TASK ---------------------------
808.  LRRA Receive Antenna Failed -Fault Isolation
A.  Description
(1)  The task is for this maintenance message:
EFFECTIVITY

34-33 TASKS 807-808
SIL ALL
Page 215 D633A103-SIL Jun 15/2010

(a)  REC ANT FAIL
B.  Possible Causes
(1)  
Receiver antenna, M1739 (No. 1) or M1740 (No. 2).

(2)
Wiring problem.

NOTE: Moisture contamination between the antenna and the airplane skin or in the antenna co-ax connector can cause false altitude output from the Radio Altimeter system.
C.  Circuit Breakers
(1)  These are the primary circuit breakers related to the fault:
CAPT Electrical System Panel, P18-1
Row Col Number Name
B 4 C01384 RADIO NAVIGATION RADIO ALTM 1

F/O Electrical System Panel, P6-1
Row Col Number Name
A 16 C01385 RADIO NAVIGATION RADIO ALTM 2

D.  Related Data
(1)
(SSM 34-33-11).

(2)
(SSM 34-33-21).

(3)
(WDM 34-33-11).

(4)
(WDM 34-33-21).

E.  Initial Evaluation
(1)  Do
this
task:
Low
Range
Radio
Altimeter
(LRRA)
BITE
Procedure,
34-33
TASK
801.

(a)  
If the red REC ANT FAIL light stays on, then do the Fault Isolation Procedure below.

(b)  
If the red REC ANT FAIL light goes off, then there was an intermittent fault.

F. Fault Isolation Procedure
(1)  Use a time domain reflectometer (TDR) test set time domain reflectometer, COM-5187to do an electrical check of the coaxial cable and antenna:
　
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