Tait TB7100 - Page 255

TB7100 Service Manual Transmitter Fault Finding (25W) 257
© Tait Electronics Limited October 2005
Task 24 —
Power Control
and Shaping Filter
In this task any faults in the power-control and shaping-filter circuitry will
be located:
1. Measure the voltage at pin 8 of IC303 (see Figure 13.9) in the
power-control circuit. The voltage should be:
2. If the voltage is correct, go to Step 3. If it is not, enter the CCTM
command 32 and return to Task 23
.
3. Measure the voltage at pin 10 of IC303 (see Figure 13.9) in the
power-control circuit. The voltage should be:
4. If the voltage is correct, go to Step 5. If it is not, go to Step 8.
5. Enter the CCTM command 32 to place the radio in receive mode.
6. Check C322, C324, R342, R347 (see Figure 13.9) in the power-
control circuit.
7. Repair any fault revealed by the checks in Step 5. Replace IC303
(see Figure 13.9) if none of the other components is faulty. Confirm
the removal of the fault and go to “Final Tasks” on page 123. If the
repair failed, replace the main-board assembly and go to “Final Tasks”
on page 123.
8. Measure the voltage at pin 1 of IC301 (see Figure 13.9) in the
shaping-filter circuit. The voltage should be:
9. Enter the CCTM command 32 to place the radio in receive mode.
10. If the voltage measured in Step 8 is correct, go to Step 11. If it is not,
go to Step 12.
11. Check the components R334 (see Figure 13.9) and C319
(see Figure 13.13) and go to Step 13.
12. Check the components between the
PWR test point and pin 1 of
IC301 (see Figure 13.9) and go to Step 13.
13. Repair any fault revealed by the checks in Step 11 and Step 12.
Replace IC301 (see Figure 13.9) if none of the other components
is faulty. Confirm the removal of the fault and go to “Final Tasks” on
page 123. If the repair failed, replace the main-board assembly and go
to “Final Tasks” on page 123.
pin 8 of IC303: 7.4 ± 0.5V
pin 10 of IC303: 4.8 ± 0.5V
pin 1 of IC301: 4.8 ± 0.5V