Tait TB8100, Service Manual

Page: 143 / 306

TB8100 Service Manual Power Amplifier Fault Finding 143
© Tait Electronics Limited September 2006
Task 4 —
Check Calibration
You can also use the Calibration Kit to help identify which section of the
PA is faulty. Refer to the Calibration Kit documentation for full details of
the calibration procedures.
1. Calibrate the PA bias. If the calibration is successful, go to Step 2 . If
the stage bias calibration fails, proceed as follows:
■
check that the correct DC supply is present at the PA
■
use the Service Kit to check the temperature of the driver, final 1
and final 2 transistors (Diagnose > Power Amplifier > Control
Tests)
■
check the final 1 and final 2 transistors (if fitted), as described in
Task 3 on page 163
■
if the final transistors are not faulty, check the driver transistor, as
described in
Task 3 on page 157 .
2. Calibrate the forward and reverse detector bias voltages. If the
calibration is successful, go to
Step 3 . If the calibration fails, go to
“Low Pass Filter and Directional Coupler Board” on page 165 .
3. Calibrate the PA power. If the calibration is successful, go to “Final
Tasks” on page 170 . If the output power is low, go to “6W Board”
on page 155 . If there is no power output, go to “Control Board” on
page 148 .
Task 5 —
Check Ambient Air
Temperature Sensor
Board
1. Run the Service Kit and connect to the base station.
2. Select Monitor > Monitoring > Power Amplifier and check that the
reading on the Air intake temperature gauge matches ambient
temperature. If it does not match, replace the ambient air
temperature sensor board.
Note
The PA fan must be in position and running to get an accurate
reading on the Air intake temperature gauge in the Service Kit.
You can use the fan test (Diagnose > Power Amplifier > Control
Tests) to make the fan run. Note also that the reading displayed
for a 100W PA may be slightly high, due to the location of the
temperature sensor board in the heatsink airflow.