Tait TM8100 mobiles, Service Manual

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302 Transmitter Fault Finding (>25W) TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
Task 19 —
Biasing of PA Driver
—
DRV
test point
If there is no fault in the biasing of the PAs, investigate the biasing of the PA
driver (Q306). First check the
DRV
test point.
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 Task 12 .
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.
2. Enter the CCTM command
304 z
(where
z
was recorded in Task 12 )
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
Table 11.6 .
If it does, go to Task 21 . If it does not, go to Step 5 .
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
DRV
test point (
CDC TX DRV BIAS
)
(see Figure 11.9 and Figure 11.10 ). The voltage should be:
7. Enter the CCTM command 304 z (where z was recorded in Task 12 )
to change the DAC value of the clamp current.
8. The voltage should increase to:
9. If the voltage does change, go to Task 20 . If it does not, go to
Step 10 .
10. Enter the CCTM command
32
to place the radio in receive mode,
and go to “CODEC and Audio Fault Finding” on page 399 .
DRV test point: < 0.1V (after entry of CCTM 304 1)
DRV test point: 0.8 to 2.5V (after entry of CCTM 304 z )