TM8100 Mobile Radio Service Manual Diagnosis of Faults on Main Board 219
May 2004 © Tait Electronics Limited
Tas k 7 —
Check Biasing
of Second PA
If there is no fault in the biasing of the first PA, check that of the second
PA (Q309).
1. Use the multimeter to measure the voltage at pin 8 of IC301 [at
3G0/3B6] (see Figure 9.17). The voltage should be 40 ± 5 mV.
Enter the CCTM command 332 b (where b was recorded in Task
5) and check that the voltage is between 2 and 5 V. Also note the
current reading; this should increase by an amount equal to the
offset noted in Step 3 of Task 5.
2. If the voltage and current are both correct, enter the CCTM
command 332 1 to turn off final bias 2, and go to Task 8. If the
voltage is correct but not the current, go to Step 3. If neither the
current nor the voltage is correct, go to Step 5.
3. If not already done, remove the
PAF TOP can. Enter the CCTM
command 332 b (where b was recorded in Task 5) and check that
the voltage at the gate of Q309 [at 3F3/3E5] is between 2 and 5 V.
If it is, Q309 is faulty; return to Subsection 8.1 and replace the
complete main-board assembly. If it is not, go to Step 4.
4. Check the circuitry between pin 8 of IC301 and the gate of Q309
(see Figure 9.17 to Figure 9.21). If a fault is found, repair it,
confirm the removal of the fault, and return to Subsection 8.1. If
the repair failed or Q309 itself is faulty, return to Subsection 8.1
and replace the complete main-board assembly.
5. Use the multimeter to measure the voltage at the
FIN2 test point [at
3K0/3B9] (see Figure 9.17). The voltage will be 18 ± 2 mV.
Enter the CCTM command 332 b (where b was recorded in Task
5) and check that the voltage is between 1.1 and 2.7 V. If it is, go
to Step 6. If it is not, go to Subsection 9.7 on the CODEC and
audio circuitry.
6. Check IC301 and the surrounding shaping-filter circuitry (see
Figure 9.17). If a fault is found, repair it, confirm the removal of
the fault, and return to Subsection 8.1. If the repair failed, return
to Subsection 8.1 and replace the complete main-board assembly.
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