Tait TM8100 mobiles Service Manual page 205

Task 12 —
VCO Faulty
Task 13 —
Check Reference
Voltage
TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
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
Related Circuitry (VHF Radios)" on page
2. If a UHF radio exhibits a lock error or a receive fault. the receive
VCO is suspect; go to
Radios)" on page
If it exhibits a system error or a transmit fault, the transmit VCO is
suspect; go to "Transmit VCO and Related Circuitry (UHF and
800MHz Radios)" on page
If the loop-filter circuitry is suspect, first check the reference voltage for
the filter.
1. Remove the
SYN BOT
2. Measure the reference voltage at pin 5 of IC505 (see
The result should be:
IC505 pin 5: 2.8 ± 0.1V DC
3. If the voltage is correct, go to
voltage circuitry is suspect; go to
4. Resolder R542 in position and check the C-multiplier Q512
(see Figure 9.8).
5. If a fault is found, repair the circuit, and confirm that the reference
voltage is now correct. If it is, go to
is not, or if no fault could be found, replace the board and go to
Tasks" on page
Step 2. With a VHF radio go to
"Receive VCO and Related Circuitry (UHF
209.
218.
can.
Task 14. If it is not, the reference-
Step
"Final Tasks" on page
163.
Frequency Synthesizer Fault Finding
"VCO and
224.
Figure
4.
163. If it
9.4).
"Final
205