TM8100 Mobile Radio Service Manual Diagnosis of Faults on Main Board 221
May 2004 © Tait Electronics Limited
Tas k 8 —
Check Biasing
of PA Driver
If there is no fault in the biasing of the PAs, check that of the PA driver
(Q306).
1. Note the current reading on the DC power supply. Enter the
CCTM command 304 c (where c was recorded in Task 5) to turn
on the clamp current; do not
specify a value higher than c.
Compare the current reading with that noted in Task 5. If the
current is correct, go to Step 5. If it is not, go to Step 2.
2. Check that the voltage from the DAC is changing by measuring
the voltage at the
DRV test point [at 3A7/3H1] (CDC TX DRV BIAS)
(see Figure 9.22). Enter the CCTM command 304 1 to turn off
the bias. The voltage should be 0.0 V. Enter the CCTM
command 304 c (where c was recorded in Task 5) to change the
DAC value of the clamp current; do not
specify a value higher
than c. The voltage should increase to between 0.8 and 2.5 V. If
it does, go to Step 3. If it does not, go to Subsection 9.7 on the
CODEC and audio circuitry.
3. Check that the voltage at the
SET PWR test point [at 3B5/3G2] (see
Figure 9.22) is between 2 and 5 V. If it is, go to Step 4. If it is
not, go to Step 5.
4. Remove the
PAD TOP can. Check that the voltage on the gate of
Q306 [at 3C3/3E3] is between 2 and 5 V. If it is, replace Q306;
confirm the removal of the fault and return to Subsection 8.1. If
it is not, go to Step 6 of Task 9.
5. Check that the power control is functional: Enter the CCTM
command 304 c (where c was recorded in Task 5). Note the
current reading on the DC power supply. Enter the CCTM
command 114 0 to switch off the power. Compare the current
reading with that noted in Step 1. If the currents in both cases are
correct, go to Task 10. If they are not, go to Step 6.
6. Check that the voltage from the DAC is changing: Measure the
voltage at the
PWR test point [at 3A9/3K1] (CDC TX PWR CTL) (see
Figure 9.22). Enter the CCTM command 114 1023. The voltage
should increase to 2.4 ± 0.1 V. If it does, go to Task 9. If it does
not, go to Subsection 9.7 on the CODEC and audio circuitry.
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