Tait TP9100 - Page 179

TP9100 Service Manual Frequency Synthesizer Fault Finding 179
© Tait Electronics Limited May 2005
Task 12 —
VCO Faulty
If the loop voltage is correct, the loop filter is functioning properly.
The VCO and related circuitry is therefore suspect. The section to proceed
to depends on the type of the radio and the nature of the fault.
1. With a UHF radio go to Step 2. With a VHF radio go to “VCO and
Related Circuitry (VHF Radios)” on page 196.
2. If a UHF radio exhibits a lock error
or a receive fault. the receive
VCO is suspect; go to “Receive VCO and Related Circuitry (UHF
Radios)” on page 183.
If it exhibits a system error
or a transmit fault, the transmit VCO is
suspect; go to “Transmit VCO and Related Circuitry (UHF
Radios)” on page 191.
Task 13 —
Check Reference
Voltage
If the loop-filter circuitry is suspect, first check the reference voltage for the
filter.
1. Remove the
SYN BOT can.
2. Measure the reference voltage at pin 5 of IC505 (see Figure 9.9).
The result should be:
3. If the voltage is correct, go to Ta sk 1 4
. If it is not, the reference-
voltage circuitry is suspect; go to Step 4.
4. Check R5017 (see Figure 9.9).
5. If a fault is found, repair the circuit, and confirm that the reference
voltage is now correct. If it is, 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 5: 2.5 ± 0.05V DC