TM9100 Service Manual Frequency Synthesizer Fault Finding 189
© Tait Electronics Limited August 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 9.4).
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 9.7)
and go to Task 15
.
3. Check IC504, IC505, Q511 (see Figure 9.4), C5085 to C5089 (B1
band, see Figure 9.7) or C5085 and C5086 (H5, H6 bands
see Figure 9.7), 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 9.7).
5. If the feedback voltage is now correct, go to “Final Tasks” on
page 147. If it is not, or if no fault could be found, replace the main-
board assembly and go to “Final Tasks” on page 147.
IC505 pin 6: 2.8 ± 0.1 V DC
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