Tait TM8235, Service Manual

Page: 266 / 578

266 Transmitter Fault Finding (40W/50W) TM8100/TM8200 Service Manual
© Tait Electronics Limited June 2006
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 11.2
(VHF) or Figure 11.3 (UHF). 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 11.2 (VHF) or
Figure 11.3 (UHF). 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 11.2
(VHF) or Figure 11.3 (UHF). 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 11.2 (VHF) or Figure 11.3 (UHF) —
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 157 . If the repair failed or the fault could not be
found, replace the board and go to “Final Tasks” on page 157 .
point 1 on R350: 13.8V DC
R339: 9V DC
point 2 on R350: < 5V DC