Tait TB8100 Service Manual

TB8100 Service Manual Power Amplifier Fault Finding 163
© Tait Electronics Limited September 2006
Task 1 —
Check Supply
Voltage
1. Set up the test equipment as shown in Figure 8.8 on page 149 (28V
PA) or Figure 8.9 on page 150 (12V PA).
2. Run the Service Kit and connect to the base station.
3. Once connected to the base station, ensure it is in Run Mode.
4. Measure the voltage at the drain of Q100. The voltage should be
28V. If it is, go to Task 2
. If it is not, go to Step 5.
5. Measure the voltage at P102 (where the DC supply wire is soldered
to the board). The voltage should be 28V. If it is, go to Task 2
. If it
is not, go to “6W Board” on page 155.
Task 2 —
Check Final
Temperature Sensor
1. Select Diagnose > Power Amplifier > Control Tests and check that
the final temperature reading is correct (e.g. if the PA is at ambient
room temperature and not transmitting, the reading on the gauge
should be approximately the same as the ambient temperature). If it
is, go to Task 3
. If it is not, go to Step 2.
2. Remove the links from SK100 (final 1) or SK101 (final 2). Using an
oscilloscope, check that data is present on pin 3 of the control board
connector. If it is, replace the 60W board. If it is not, replace the
control board and go to Task 3
.
Task 3 —
Check Final
Transistor
Also carry out this task if you have tried to calibrate the PA bias in Ta sk 4
on page 143 and the final calibration failed.
1. Disconnect the DC supply from the PA.
2. Measure the DC resistance between the gate of Q100 and ground (in
a 100W PA check both final transistors before going to Step 3). If
the resistance is greater than 5k ohms, go to Step 3. If it is less than
5k ohms, replace Q100 and repeat this test (refer to “Replacing the
60W RF Power Transistor” on page 184).
3. Reconnect the DC supply to the PA.
4. Check that 28V is present on the drain of Q100. If it is, go to Step 5.
If it is not, replace the 60W board.
5. Connect an oscilloscope across pin 2 of SK100 or SK101
(FINAL-BIAS) and ground.
6. Use the Calibration Kit to calibrate the PA bias. Check that the
FINAL-BIAS voltage ramps from 0V to 5V during calibration. If it
does, replace the 60W board. If it does not, replace the control board
and go to Task 4
.

Tait TB8100 Specifications

General

Brand	Tait
Model	TB8100
Category	Accessories
Language	English