TM8100 Mobile Radio Service Manual Diagnosis of Faults on Main Board 235
May 2004 © Tait Electronics Limited
7. If not already done, remove the PAF TOP can. Check for an open
circuit between the test capacitor and the common drain of Q309
[at 3F3/3E5] and Q310 [at 3F2/3D5] (see Figure 9.18 and
Figure 9.19 as well as Figure 9.27 and Figure 9.28). Also check
for faulty, shorted or misplaced components in this part of the
circuit. Repair any fault.
8. Repeat Steps 1 to 4 of Task 14. Remove the test lead and test
capacitor, and resolder the coupling capacitors in position. If the
power and current are now correct at all three frequencies, the
fault has been rectified; return to Subsection 8.1. If they are not,
go to Task 10.
Task 16 —
Power and Current
Are Low
If the RF output power and the supply current are uniformly low at all
frequencies, one of the PAs is suspect or the input to the PAs is reduced.
Check each PA in turn:
1. For the first PA (Q310), enter the CCTM command 331 to check
the DAC value of final bias 1 (
CDC TX FIN BIAS 1). Record the value
a returned.
2. Note the current reading on the DC power supply. Enter the
CCTM command 331 1 to turn off final bias 1.
3. Enter the CCTM command 33 to place the radio in transmit
mode. Note the RF output power measured at the test set. This
should be as shown in Table 9.10. If it is, go to Step 4 to repeat
the check with the second PA. If it is not, carry out Task 5 and
then Task 6.
4. For the second PA (Q309), enter the CCTM command 332 to
check the DAC value of final bias 2 (
CDC TX FIN BIAS 2). Record the
value b returned.
5. Note the current reading on the DC power supply. Enter the
CCTM command 332 1 to turn off final bias 2.
6. With the radio still in transmit mode, note the RF output power
measured at the test set. This should be as shown in Table 9.10.
If it is, go to Task 10. If it is not, carry out Task 5 and then Task 7.
Table 9.11 RF output power of individual RF power amplifiers at different frequencies
Frequency band
Frequency within band
Lowest frequency Centre frequency Highest frequency
B1 29 ± 5 W 34 ± 5 W 29 ± 5 W
D1 33 ± 5 W 28 ± 5 W 29 ± 5 W
H5 5 ± 5 W 12 ± 5 W 27 ± 5 W
H6 13 ± 5 W 19 ± 5 W 28 ± 5 W
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