Tait TB7100, Service Manual

Page: 161 / 370

TB7100 Service Manual Frequency Synthesizer Fault Finding 163
© Tait Electronics Limited October 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 11.4 ).
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 11.7 )
and go to Task 15 .
3. Check IC504, IC505, Q511 (see Figure 11.4 ), C5085 to C5089
(B1 band, see Figure 11.7 ) or C5085 and C5086 (H5, H6 bands
see Figure 11.7 ), 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 11.7 ).
5. If the feedback voltage is now correct, go to “Final Tasks” on
page 123 . If it is not, or if no fault could be found, replace the main-
board assembly and go to “Final Tasks” on page 123 .
IC505 pin 6: 2.8
±
0.1 V DC