148 Frequency Synthesizer Fault Finding TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 3 —
14V Power Supply
First check the output VCL SUPPLY from the SMPS, which is itself provided
with a 9V DC supply from a 9V regulator in the PSU module.
1. Remove the main-board assembly from the chassis.
2. Place the radio in CCTM.
3. Measure the SMPS output
VCL SUPPLY at the via between C531 and
R530 (see Figure 11.2).
4. If the SMPS output is correct, go to Task 4
. If it is not, go to Step 5.
5. Check the 9 V supply at Q500 and R533 (see Figure 11.3).
6. If the voltage is correct, go to Step 7. If it is not, the 9V regulator
IC601 is suspect; go to Task 3
of “Power Supply Fault Finding” on
page 132.
7. Remove the
FCL TOP can and check the SMPS circuit based on Q500,
Q502 and L502 (see Figure 11.3).
Remove the
SYN BOT can and check IC504 and IC505 for shorts
(see Figure 11.4); replace any suspect IC.
8. If a fault is found, repair the circuit, confirm the removal of the fault,
and go to “Final Tasks” on page 123. If the repair failed or no fault
could be found, replace the main-board assembly and go to “Final
Tasks” on page 123.
C531: 14.2 V ± 0.3 DC
Q500 and R533: 9.0 V ± 0.3 DC
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