TM8100/TM8200 Service Manual Frequency Synthesizer Fault Finding 189
© Tait Electronics Limited June 2006
Task 5 —
5V Power Supply
If the SMPS output and 6V DC supply are correct, check the +5V DEC
supply next.
1. Remove the
SYN TOP can.
2. Measure the supply +5
V DEC at pin 4 of Q508 (see Figure 9.2).
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 Q506, Q507
and Q508 (pins 1, 2, 6) (see Figure 9.2). 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 Q5004 (see Figure 9.2). Remove the
SYN TOP
can (A4 band only) and
VCO BOT can, and check the transmit-receive
switch based on Q5002 and Q5003 (see Figure 9.5). Replace any
suspect transistor. 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 157. If the repair failed or no fault
could be found, replace the board and go to “Final Tasks” on
page 157.
pin 4 of Q508: 5.3 ± 0.3V DC
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