TM8100 Mobile Radio Service Manual Diagnosis of Faults on Main Board 223
May 2004 © Tait Electronics Limited
Tas k 9 —
Repair Circuitry
Following the checks in Task 8, locate and repair the fault in the circuitry
as follows:
1. Cycle the power. Enter the CCTM command 326 5 to set the
transmitter to maximum power. Enter the CCTM command 33
to place the radio in transmit mode. Measure the voltage at pin 9
of IC303 [at 3E7/3H4] in the power-control circuit (see
Figure 9.22). The voltage should be as given in Table 9.7. If it is,
go to Step 3. If it is not, go to Step 2.
2. Check the voltage at pin 5 of IC303 [at 3J7/3H8] (or use the
FWD PWR test point). The voltage should be as given in Table 9.7.
If it is, check the components between pins 6 and 7 of IC303 (see
Figure 9.23 and Figure 9.24) [R340, C3090, R3090 (B1 band) or
R340, C345, R3009 (D1, H5, H6)]. If it is not, check the
components of the directional coupler (see Figure 9.27). In either
case repair any fault. Replace IC303 if necessary. 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.
3. Measure the voltage at pin 8 of IC303 [at 3D7/3H4] in the power-
control circuit. The voltage should be 7.4 ± 0.5 V. If it is not, go
to Step 5. If it is, measure the voltage at pin 10 of IC303. The
voltage should be 4.8 ± 0.5 V. If it is, go to Step 4. If it is not, go
to Step 5.
4. Check C322, C324, R342, R347 (see Figure 9.22) and R396 (see
Figure 9.23 and Figure 9.24) in the power-control circuit. Repair
any fault. If these components are not faulty, replace IC303.
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.
5. Measure the voltage at pin 1 of IC301 [at 3C8/3J3] in the power-
control circuit. The voltage should be 4.8 ± 0.5 V. If it is, check
the components R334 (see Figure 9.22) and C319 (see
Figure 9.23 and Figure 9.24) [at 3D8/3J4]. If it is not, check the
components between the
PWR test point [at 3A9/3K1] and pin 1
of IC301 (see Figure 9.22). Repair any fault. Replace IC301 if
necessary. 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.
6. Check for short circuits at the gate of the PA driver Q306 [at
3C3/3E3]. Check R333, R336 [at 3D7/3H3] (see Figure 9.22),
C310, R324 and R327 [at 3C4/3F2] (see Figure 9.20 and
Figure 9.21) between the power-control circuit and Q306.
Repair any fault. If these components are not faulty, replace
Q306. 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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