168 Frequency Synthesizer Fault Finding TP9100 Service Manual
© Tait Electronics Limited May 2005
Task 5 —
4.3V Power Supply
If the SMPS output and 5V DC supply are correct, check the +4V3 DEC
supply next.
1. Remove the
SYN TOP can.
2. Measure the supply +4
V3 DEC at pin 4 of Q508 (see Figure 9.3).
3. If the voltage is correct, go to Tas k 6
. If it is not, go to Step 4 (UHF
radios) or Step 5 (VHF radios).
4. With a UHF radio check for faults in the C-multiplier Q508 (pins 3,
4, 5) and the 5V and transmit-receive switches based on Q513, Q507
and Q508 (pins 1, 2, 6) (see Figure 9.3). Replace any suspect
transistor. Conclude with Step 6.
5. With a VHF radio check for faults in the C-multiplier and 5V switch
based on Q508 and Q513 (see Figure 9.3). Check the operation of
Q517 and Q513. Conclude with Step 6.
6. If a fault is found, repair the circuit, confirm the removal of the fault,
and go to “Final Tasks” on page 134. If the repair failed or no fault
could be found, replace the main board, and go to “Final Tasks” on
page 134.
pin 4 of Q508: 4.3 ± 0.15V DC
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