TM8100 Mobile Radio Service Manual Diagnosis of Faults on Main Board 215
May 2004 © Tait Electronics Limited
Tas k 6 —
Check Biasing
of First PA
Check the biasing of the first PA (Q310).
1. Use a multimeter to measure the voltage at pin 14 of IC301 [at
3G1/3C6] (see Figure 9.17). The voltage will be 40 ± 5 mV.
Enter the CCTM command 331 a (where a 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 2 of Task 5.
2. If the voltage and current are both correct, enter the CCTM
command 331 1 to turn off final bias 1, and go to Task 7. 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 331 a (where a was recorded in Task 5) and check that
the voltage at the gate of Q310 [at 3F2/3D5] is between 2 and 5
V. If it is, Q310 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 14 of IC301 and the gate of
Q310 (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 Q310 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
FIN1 test point [at
3J1/3C8] (see Figure 9.17). The voltage will be 18 ± 2 mV.
Enter the CCTM command 331 a (where a 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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