Nautel XR6, Руководство по устранению неисправностей, Страница: 55 / 291

XR6/XR3 Troubleshooting Manual Responding to alarms
Issue 3.0 2009-07-15 Page 1-35
RF drive tuning check
Verify the RF drive tuning circuit is functional and the RF drive's tuned circuits are resonant, or can
be tuned to resonance at the host transmitter's carrier frequency (
f c).
Perform RF drive tuning check as follows.
See
Figure 1.6 on page 1-34 and Figure 1.7 on page 1-34 .
1. Remove the cover from the RF drive tuning assembly and loosen the locking hardware.
Reinstall the cover.
2. Using an oscilloscope and 10X oscilloscope probes, monitor the RF voltage and RF current
at TP14 and TP15 of the RF drive control PWB.
3. Adjust the RF drive tuning assembly's RF drive screw, using a 10 mm nut driver, until the
zero crossing points of the two waveforms in Step 1 coincide.
4. Remove the jumper installed in “Test cable connection” , Step 8. on page 1-31 .
5. Remove the cover from the RF drive tuning assembly and tighten the locking hardware.
Reinstall the cover.
Temp/inhibit check
The
Temp/Inhibit
LED will turn on when the temperature of at least one heatsink exceeds 85°C.
Troubleshoot a
Temp/Inhibit
alarm as follows:
1. Check the temperature of the RF amplifier/modulator heatsinks. If either heatsink is hot
(approximately 85°C), suspect either a fan failure in the host transmitter or a frequency
problem in the RF power module. See
“RF drive tuning check” on page 1-35 in the case of
the latter. If the heatsinks are cooler than 85°C, proceed to Step 2 .
2. Measure the dc voltage at U3-3 of the RF drive control PWB (A1). The voltage should be
greater than 20 V. If so, suspect the RF drive control PWB.
3. Measure the dc voltage at U2-6 of the RF drive control PWB (A1). The voltage should be
greater than 5 V. If so, suspect the RF drive control PWB.
4. If the voltage in Step 3 is less than 5 V, suspect a fault with either thermistor RT1 or RT2,
noting they are located above the RF amplifiers on the RF power module’s chassis.