Nautel XR6, Troubleshooting Manual, Page: 50 / 291

XR6/XR3 Troubleshooting Manual Responding to alarms
Page 1-30 Issue 3.0 2009-07-15
6. Verify the test circuit is applying the dc voltages required by the RF power module. Use a
multimeter to measure the dc voltages as tabulated in Table 1.4 .
7. Verify the alarm circuitry is operating properly by pressing
Reset
in the
Status
screen of the
host transmitter’s GUI. The
Temp/Inhibit
alarm should turn off, and the
Block
alarms
should remain on. Then press the power module's
Inhibit
button and the
Temp/Inhibit
alarm should turn on.
If the
Temp/Inhibit
alarm LED will not turn off and on as indicated, there is a fault with the
alarm circuitry on the RF drive control PWB. This fault must be repaired before proceeding.
If the
RF Drive
alarm LED remains on after
Reset
is pressed, proceed to “RF drive tuning
NOTE:
The RF power module may be connected to the transmitter’s test circuit without turning the
transmitter off or interrupting its on-air operation.
The host transmitter must be turned on and its RF power stage must be enabled (its
RF On
LED must be on) for dc voltages to be applied to the RF power module.
Sufficient output power must be provided to allow the PDM signals, generated by the
transmitter, to drive the module under test. Use an oscilloscope to measure the duty cycle on
TP17 of the interphase PDM driver PWB. Increase power until the duty cycle is above 30%.
The RF power module's
Block
(
A
,
B
,
C
and
D
) alarm LEDs will be on when the module is
connected to the test circuit. This is normal operation and does not mean the modulators have
failed. This false alarm is an indication that the modulator failure detector circuit is functioning,
since the reduced test B+ voltage (48 V dc) is seen to be a modulator failure.
Table 1.4: Dc Voltages Provided By Transmitter
Test Point Voltage
A14-F1 48 V
A1L1 24 V
A1L2 15 V
A1L3 5 V