Tait TB7100, Service Manual

Page: 168 / 370

170 Frequency Synthesizer Fault Finding TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 18 —
Repair PLL feedback
If both the minimum and maximum receive frequencies are correct, the
PLL feedback is suspect.
1. Resolder R542 in position (see Figure 11.9 ).
2. Remove the
VCO BOT
can.
3. Replace the components C567, R574 (see Figure 11.10 ) and
IC503 (see Figure 11.9 ).
4. Also check the second stage of the receive buffer amplifier based on
IC5100
(see Figure 11.10 ). Repair any fault.
5. Confirm that the fault in the radio has been removed. If it has, go to
“Final Tasks” on page 123 . If it has not, replace the main-board
assembly and go to “Final Tasks” on page 123 .
Figure 11.10 Synthesizer circuitry under the
VCO BOT
can
(UHF radio, bottom side)
Q5001