254 Transmitter Fault Finding (50W/40W Radios) TM9100 Service Manual
© Tait Electronics Limited August 2005
Task 2 —
Check Switch Circuit
If the power supply to the drains of the PAs and PA driver is not correct, the
switch circuit is suspect. Check the circuit as follows:
1. Measure the voltage at the point 1 on R350 shown in Figure 11.4
(B1 band) or Figure 11.5 (H5, H7 bands). The voltage should be:
2. If the voltage measured in Step 1 is correct, go to Step 3. If it is not,
check for continuity between R350 and the power connector. Repair
any fault and conclude with Step 8.
3. Measure the voltage at R339 as shown in Figure 11.4 (B1 band) or
Figure 11.5 (H5, H7 bands). The voltage should be:
4. If the voltage measured in Step 3 is correct, go to Step 5. If it is not,
go to Task 3
and check the 9V power supply.
5. Measure the voltage at the point 2 on R350 shown in Figure 11.4
(B1 band) or Figure 11.5 (H5, H7 bands). The voltage should be:
6. If the voltage measured in Step 5 is correct, go to Step 7. If it is not,
replace Q308 — see Figure 11.4 (B1 band) or Figure 11.5 (H5,
H7 bands) — and conclude with Step 8.
7. Remove the heat-transfer block from the main board. Replace Q311
(situated on the bottom-side of the main board next to the power
connector). Replace the heat-transfer block, and conclude with
Step 8.
8. Repeat Task 1
to confirm the removal of the fault, and go to “Final
Tasks” on page 147. If the repair failed or the fault could not be
found, replace the main-board assembly and go to “Final Tasks” on
page 147.
point 1 on R350: 13.8V DC
R339: 9V DC
point 2 on R350: < 5V DC
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