Tait TP9100 - Page 180

180 Frequency Synthesizer Fault Finding TP9100 Service Manual
© Tait Electronics Limited May 2005
Task 14 —
Check Feedback
Voltage
If the loop filter is suspect but the reference voltage is correct, check the
feedback voltage.
1. Measure the feedback voltage at pin 6 of IC505 (see Figure 9.9).
The result should be:
2. If the voltage is not correct, the loop filter is faulty; go to Step 3.
If the voltage is correct, resolder R542 in position (see Figure 9.8)
and go to Ta s k 1 5
.
3. Check IC504, IC505, Q511 (see Figure 9.9), C548
(see Figure 9.8), and associated components.
4. If a fault is found, repair the circuit, repeat the measurement of the
feedback voltage in Step 1, and resolder R542 in position
(see Figure 9.8).
5. If the feedback voltage is now correct, go to “Final Tasks” on
page 134. If it is not, or if no fault could be found, replace the main
board, and go to “Final Tasks” on page 134.
IC505 pin 6: 2.5 ± 0.1V DC