a. If the problem follows the module, check the drive phas-
ing, RF drive toroid transformers, and the MOSFET’s.
b. If the phase problem remains at the same module position
with different modules, investigate possible problems in
the combiner toroid or efficiency coil tapping.
6.31.8.2 Measuring Steps 57-90: TEST SWITCH
To measure drain signals on RF amplifiers RF57 to RF90, the
FlexPatch™ TEST SWITCH feature is used:
a. Remove the gold jumper from the FlexPatch™ plug for
the RF amplifier step to be measured. The FlexPatch™
plug is located on the Modulation Encoder.
b. Remove any FlexPatch™ jumper cables from the holes in
P8-1 and 2. P8 is located next to the RF amplifier TEST
SWITCH S2 on the Modulation Encoder.
c. Insert one end of a FlexPatch™ cable into P8-1. Connect
the other end of the jumper to the hole closest to the PA
Modules of the jack where the gold jumper was removed.
d. Operate the transmitter at 25 kW. The reference phase
should already have been set in the preceding steps. Note
that the drive waveform zero crossing on the module to
be measured will not be visible because the RF amplifier
is not turned ON.
e. Depress TEST SWITCH S2 and note that the drain is now
turned ON as indicated by a zero crossing now indicating
drain phase. The drain phasing of this RF amplifier can
now be measured.
Section VI - Troubleshooting
Rev. R: 11-11-96 888-2297-002 6-21
WARNING: Disconnect primary power prior to servicing.
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