330 Transmitter Fault Finding (25W) 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 12.3.
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 12.3. 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 12.3.
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 12.3 — and conclude with Step 8.
7. Remove the heat-transfer block from the board. Replace Q311
(situated on the bottom-side of the board next to the power
connector). Replace the heat-transfer block, and conclude with
Step 8.
8. Repeat Ta s k 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.
Task 3 —
9V Power Supply
If the supply from the power connector is correct, check the 9V DC supply.
1. Enter the CCTM command 326 1 to set the transmitter power level
very low.
2. Enter the CCTM command 33 to place the radio in transmit mode.
3. Measure the supply voltage between the 9
V0 TX test point and the
GND test point (see Figure 12.4).
4. Enter the CCTM command 32 to place the radio in receive mode.
5. If the supply measured in Step 3 is correct, go to Task 4
in
“Transmitter RF Power” on page 334. If it is not, the 9V regulator
IC601 and the associated switching circuitry Q603 are suspect; go to
Tas k 3
of “Power Supply Fault Finding” on page 168.
point 1 on R350: 13.8V DC
R339: 9V DC
point 2 on R350: < 5V DC
supply 9V0 TX: 9.0 ± 0.5V DC
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