Biasing Of Pa Driver And Pas - Tait TM8235 Service Manual

12.3

Biasing of PA Driver and PAs

Introduction
Task 12 —
Prepare to
Check Biasing
342 Transmitter Fault Finding (25W)
The measurements of the transmitter RF output power in
Power" might indicate a need to check the biasing of the two PAs and the
PA driver. The procedure is covered in this section. There are thirteen tasks
grouped as follows:
Task 12: prepare to check biasing
Task 13 to Task 15: check biasing of first PA
Task 16 to Task 18: check biasing of second PA
Task 19 and Task 20: check biasing of PA driver
Task 21 to Task 24: repair circuitry
The test and measurement points for diagnosing faults in the biasing of the
PAs and PA driver are summarized in
If the transmitter is not being inhibited, check the biasing of the two PAs
and the PA driver. First make the following preparations:
1. Set the current limit on the DC power supply to 2A.
Enter the CCTM command 331 to check the DAC value of final bias
2.
1 (
CDC TX FIN BIAS
Enter the CCTM command 332 to check the DAC value of final bias
3.
2 (
CDC TX FIN BIAS
Enter the CCTM command 304 to check the DAC value of the
4.
clamp current at the driver gate. Record the value z returned.
5. Enter the CCTM command 33 to place the radio in transmit mode.
6. Switch off all biases by entering the following CCTM commands in
sequence:
331 1
332 1
304 1
114 1023
334 0
335 0
7. Note the current reading on the DC power supply. This will be less
than 500mA.
8. With the radio still in transmit mode, check the biasing of the PAs and
PA driver, beginning with
Figure
1) at maximum power. Record the value x returned.
2) at maximum power. Record the value y returned.
Task 13.
"Transmitter RF
12.7.
TM8100/TM8200 Service Manual
© Tait Electronics Limited June 2006