230 Transmitter Fault Finding TP9100 Service Manual
© Tait Electronics Limited May 2005
10.3 Biasing of PA Driver and PA
Introduction The measurements of the transmitter RF output power in “Transmitter RF
Power” might indicate a need to check the biasing of the PA and the PA
driver. The procedure is covered in this section. The tasks are grouped as
follows:
■ Task 9: prepare to check biasing
■ Task 10 to Task 12: check biasing of PA
■ Task 13 to Task 14: check biasing of PA driver
■ Task 15 to Task 17: repair circuitry
The test and measurement points for diagnosing faults in the biasing of the
PA and PA driver are summarized in Figure 10.6 on page 231.
Important The
PA BOT can must not be removed while the radio is in
transmit mode.
To access the measurement and test points, remove the
TX CONTROL BOT and
PA BOT cans.
Task 9 —
Prepare to
Check Biasing
If the transmitter is not being inhibited, check the biasing of the PA.
First make the following preparations:
1. Set the current limit on the DC power supply to 2 A.
2. Enter the CCTM command 331 to check the DAC value of final bias
1 (
CDC TX FIN BIAS) at high power (CCTM command 326 4).
Record the value x returned.
3. Enter the CCTM command 33 to place the radio in transmit mode.
4. Switch off all biases by entering the following CCTM commands in
sequence:
■ 331 1
■ 326 4 (set to high power)
5. Note the current reading on the DC power supply. This will be less
than 550mA.
6. With the radio still in transmit mode, check the biasing of the PA,
beginning with Task 10
.
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