TM8100 Mobile Radio Service Manual Diagnosis of Faults on Main Board 201
May 2004 © Tait Electronics Limited
6. Having excluded the IF amplifier, check all remaining
components between T401 [at 4L6/4G10] and IC400 [at
4M1/4C10] — these form the matching circuitry for the crystal
filters XF400 [at 4N6/4G12] and XF401 [at 4Q2/4D13] (see
Figure 9.13). If there is no fault, go to Task 3. If there is, repair
the fault and go to Step 7.
7. Recalibrate the receiver using the calibration application.
Confirm the removal of the fault and return to Subsection 8.1. If
the repair failed, go to Task 3.
Tas k 3 —
Receiver Sensitivity Is
About 15 dB Too Low
If the receiver sensitivity is about 15 dB too low, the fault is probably in
the front-end tuning circuitry.
1. Using the calibration application, check the calibration of the
front-end tuning circuitry: Open the “Raw Data” page and click
the “Receiver” tab. Record the values listed in the “Rx FE Tune BPF
Settings” field — these are the DAC values of the FE (front-end)
tuning voltages for the five frequencies FE TUNE0 to FE TUNE4.
(FE TUNE0 is the lowest frequency and FE TUNE4 the highest
frequency in the radio’s frequency band.)
2. For each of the frequencies FE TUNE0 to FE TUNE4 in turn, carry
out the following procedure: Enter the CCTM command
101 aa0, where a is the frequency in hertz. Enter the CCTM
command 376 and record the value returned — this is the front-
end tuning voltage in millivolts.
3. Compare the values measured in Steps 1 and 2 with the nominal
DAC and voltage values listed in Table 9.3. If the values are
correct, go to Step 4. If they are not, recalibrate the receiver using
the calibration application, and check the DAC and voltage values
again. If the values are now correct, the fault has been rectified;
return to Subsection 8.1. If they are not, go to Step 4.
4. Remove the
FE TOP and IF TOP cans. Check the soldering of all the
components of the front-end tuning circuitry from C400 [at
4B6/4G1] to T401 [at 4L6/4G10] (see Figure 9.13 and
Figure 9.15). Check the supply voltage at L404 [at 4E7/4H5].
Also check the LNA bias conditions: V
c
should be 2.7 ± 0.1 V
and I
c
should be 10 ± 1 mA. Measure V
c
between the collector
of Q401 [at 4F6/4G5] and the point shown in Figure 9.15. To
check I
c
, unsolder and raise one terminal of L404 (tombstone
position), connect a multimeter between this terminal and the pad
for the terminal, and measure the current. If there is no fault, go
to Step 5. If there is, repair the fault and go to Step 6.
5. Check the signal level at the output of LO1 and continue the fault
diagnosis as in Subsection 9.3 on the frequency synthesizer.
6. Recalibrate the receiver using the calibration application.
Confirm the removal of the fault and return to Subsection 8.1. If
the repair failed, go to Task 4.
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