Nautel XR12, Troubleshooting Manual, Page: 37 / 283

XR12 Troubleshooting Manual Responding to alarms
Issue 3.0 2009-07-28 Page 1-17
Auto changeover
This event is caused by a fault in the active exciter with the Auto Changeover function enabled. Faults
that cause exciter changeovers are:
Mod Driver Fail A/B
,
RF Driver Fail
and
PDM Drive Fail
.
• This event triggers the
Changeover
LED to light, and it will remain lit until manually
cleared.
• No further auto changeovers are possible until the alarm is cleared.
• The alarm can be cleared remotely by re-selecting the active exciter.
• The alarm can be cleared locally by use of the Preset screen.
An
Auto Changeover
alarm indicates that the standby exciter is operating and that the transmitter
has switched from main exciter to standby exciter. The
Auto Changeover
alarm may be caused by a
fault in the transmitter that initiated an automatic exciter changeover, or a fault in the control/display
PWB's microprocessor or alarm circuit. Troubleshoot the
Auto Changeover
alarm as follows:
1. Check the
Events Log
to determine the possible cause of the exciter changeover.
2. Troubleshoot any alarms recorded in the
Events Log
to determine the cause of the exciter
changeover.
RF driver fail
This fault indicates a problem with the RF drive on the current exciter. If the exciter transfer function
is set to
auto then the microcontroller will attempt an exciter changeover to the standby exciter. If it
cannot complete an exciter changeover, or if the exciter transfer function is set to manual , then this
fault will cause a shutback.
An
RF Driver Fail
alarm indicates an incorrect voltage waveform in the RF drive buffer PWB. The
alarm could result from a failure in the RF drive buffer PWB, RF synthesizer PWB, or in the control/
display PWB's alarm circuitry. Troubleshoot an
RF Driver Fail
alarm as follows:
1. The
RF Driver Fail
alarm initiates an automatic exciter changeover to the standby exciter. To
troubleshoot a defective exciter circuit, set changeover to manual as detailed in “Changing
automation settings” in the Operating and Maintenance Manual .
2. Use an oscilloscope to measure TP7 of the RF synthesizer PWB. The signal should be a 15
volt peak-to-peak square wave at the carrier frequency. If the signal is present, suspect the RF
drive buffer PWB. Otherwise suspect the RF synthesizer PWB.