Glenayre Document Number: 9110.01002
GL-T8541 PA
09/10/99
CHECKOUT AND MAINTENANCE
t8541
p7.
fdk
Copyright © 1997 Glenayre
Page: 7-15
7.11 Advanced Troubleshooting
Some additional tips will be useful in the event of a failure of one or more of the RF power
transistors in the GL-T8541 PA module. The most common failure mode for these FET
transistors is a low resistance path between the gate and source.
The RF power transistors are contained in the driver and final PA boards. Different trou-
bleshooting methods are required for the driver board and the PA boards.
A VDT or personal computer with VT100 emulation capabilities is required to obtain status
or fault readings or to perform programming and many of the calibration procedures for this
PA. A straight through DE-9 to DE-9 cable or an EIA-232 DE-9 to DB-25 adaptor cable is
needed to connect from the serial port of the computer or VDT to the female DE-9
connector on the front of the DSP exciter or the C2000 controller.
7.11.1 Checking PA Module Supply Voltage
Each PA board and the driver board receives its own fused, current mon28 volt
supply from the metering board. The metering board receives its +28 volt supply from the
power supply. The VDT PA 28V indication monitors the metering board +28 volt input.
7.11.1.1
Open Transistor or Blown Fuse
The normal effect of a failed driver or PA board transistor is a lower than normal VDT
current. A blown metering board fuse results in zero current flow from its PA or driver
board.
At the transmitter site, the metering board fuses are easily checked by:
1.
Remove power to the transmitter.
2.
Swing the fan panel open
3.
Individually remove and check the metering board fuses. Refer to Figure 7-1. The
fuses for each board are listed below.
4.
Replace the open fuses and reconfigure transmitter to normal.
7.11.1.2
Measuring PA Module Voltages
The supply voltage to each board of the PA module can be measured if a blank panel of at
least 2 RU is situated immediately above the transmitter chassis. The following procedure
can be used to measure dc voltages within the PA module.
1.
Remove power to the transmitter.
2.
Remove the blank panel immediately above the PA module.
Driver
F1
PA 1
F3
PA 2
F6
PA 3
F8
