Biasing Of Pa Driver - Drv Test Point - Tait TM9100 Service Manual

If there is no fault in the biasing of the PAs, investigate the biasing of the PA
Task 19 —
Biasing of
driver (Q306). First check the
PA Driver—
test point
DRV
Important
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
TM9100 Service Manual
© Tait Electronics Limited August 2005
DRV
Ensure that the current limit on the DC supply is 2A.
And, when entering the CCTM command 304 z, do not
specify a value z higher than that recorded in
Failure to do so might result in the destruction of the PA
driver.
Note the current reading on the DC power supply. As mentioned in
Step 7 of Task 12, the current will be less than 500mA.
Enter the CCTM command 304 z (where z was recorded in
to switch on the clamp current.
Note the current reading on the DC power supply.
Compare the above current readings. The current should increase by
an amount approximately equal to the offset given in
If it does, go to Task 21. If it does not, go to
Check as follows that the voltage from the DAC is changing:
First enter the CCTM command 304 1 to switch off the bias.
Measure the voltage at the
(see Figure 12.9). The voltage should be:
DRV test point: < 0.1V (after entry of CCTM 304 1)
Enter the CCTM command 304 z (where z was recorded in
to change the DAC value of the clamp current.
The voltage should increase to:
DRV test point: 0.8 to 2.5V (after entry of CCTM 304 z)
If the voltage does change, go to
Step 10.
Enter the CCTM command 32 to place the radio in receive mode,
and go to "CODEC and Audio Fault Finding" on page
Transmitter Fault Finding (25W Radios)
test point.
Step 5.
test point (
DRV CDC TX DRV BIAS
Task 20. If it does not, go to
Task 12.
Task 12)
Table 12.6.
)
Task 12)
371.
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