Nautel XR6, Troubleshooting Manual, Page: 36 / 291

XR6/XR3 Troubleshooting Manual Responding to alarms
Page 1-16 Issue 3.0 2009-07-15
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.
3. Use an oscilloscope to measure TP2 of the RF drive buffer 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.
4. Measure the dc voltage at TP1 of the RF drive buffer PWB. If the voltage is less than 0.6 V,
suspect the control/display PWB or transistor Q1 on the RF drive buffer PWB.
Cutback level (1-8)
Should there be three shutbacks within five seconds, the transmitter will enter a power reduction
mode called a cutback.
There are eight levels of cutbacks, the last being a reduction to no forward power whatsoever. At any
given cutback level, there is a predefined time limit that must expire before the cutback level is
reduced to the previous level. If there are no further cutbacks, this process continues until Level 0
(normal) is reached.
The cutback recovery process can be overridden by adjusting the power (up or down), or by pressing
Reset
on the
Status
screen.