Tait TM8100 mobiles Service Manual page 302

Task 19 —
Biasing of PA Driver
— test point
DRV
302 Transmitter Fault Finding (>25W)
If there is no fault in the biasing of the PAs, investigate the biasing of the PA
driver (Q306). First check the
Important
Ensure that the current limit on the DC supply is 1A.
And, when entering the CCTM command 304 z, do not
specify a value z higher than that recorded in
Failure to do so may result in the destruction of the
PA driver.
1. 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
2.
to switch on the clamp current.
3. Note the current reading on the DC power supply.
4. Compare the above current readings. The current should increase by
an amount approximately equal to the offset given in
If it does, go to
5. Check as follows that the voltage from the DAC is changing:
First enter the CCTM command 304 1 to switch off the bias.
6. Measure the voltage at the
(see Figure 11.9
DRV test point: < 0.1V (after entry of CCTM 304 1)
Enter the CCTM command 304 z (where z was recorded in
7.
to change the DAC value of the clamp current.
8. The voltage should increase to:
DRV test point: 0.8 to 2.5V (after entry of CCTM 304 z)
9. If the voltage does change, go to
Step 10.
Enter the CCTM command 32 to place the radio in receive mode,
10.
and go to "CODEC and Audio Fault Finding" on page
test point.
DRV
Task 21. If it does not, go to
test point (
DRV
and Figure 11.10). The voltage should be:
Task
© Tait Electronics Limited November 2007
Task
Task
Table
Step 5.
)
CDC TX DRV BIAS
Task
20. If it does not, go to
399.
TM8100/TM8200 Service Manual
12.
12)
11.6.
12)