Motorola VSWR, Service Manual Supplement

Page: 43 / 44

Troubleshooting the VM
5th Feb 99 Service Manual Supplement: VSWR Monitor for M-Cell 6
68P02900W86-O
3–1
Troubleshooting the VM
Introduction to
VM maintenance
This part of the supplement provides all the information required to determine whether or
not a failure is due to a defective VSWR Monitor (VM) and how to replace a VM.
Symptoms of a
defective VM
Power failure
A VM internal power failure is indicated if the green dc power LED is not illuminated when
the external –48 V dc supply is connected and known to be working.
False alarms
For a “true” false alarm to occur (thus indicating a failure within the VM), all of the
following conditions must be met:
1. A Tx/Rx alarm signal from the VM has been received by the BTS.
2. The BTS is transmitting and receiving normally.
3. The jumper settings for unused VM connections have been set to OFF (if
applicable).
4. One or more of the alarm LEDs on the VM is illuminated.
If conditions 1 to 3 above have been met but none of the alarm LEDs are
illuminated (condition 4), this indicates that the false alarm has been caused by
a fault in the alarm wiring and not the VM. This can be checked by carrying out
the test procedure described in Testing the VM
.
NOTE