Tait TP9100 Service Manual

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TP9100 Service Manual Frequency Synthesizer Fault Finding 193© Tait Electronics Limited May 2005Task 24 óRepair PLL feedbackIf both the minimum and maximum transmit frequencies are correct, thePLL feedback is suspect.1. Resolder R542 in position (see Figure 9.11).2. Remove the VCO BOT can.3. Replace the components C570, R578 (see Figure 9.13) and IC503(see Figure 9.11).4. Confirm that the fault in the radio has been removed. If it has, go to“Final Tasks” on page 134. If it has not, replace the main board, andgo to “Final Tasks” on page 134.Task 25 óRepair TransmitVCOIf either or both the minimum and maximum transmit frequencies areincorrect, the transmit VCO circuitry is faulty.1. Remove the VCO TOP can.2. Check the transmit VCO. The circuitry is based on Q510(see Figure 9.11).3. If a fault is found, repair it and go to Step 4. If no fault is found, goto Step 6.4. Repeat the frequency measurements in Step 2 and Step 4 of Task 23.5. If the frequencies are now correct, resolder R542 in position(see Figure 9.11), and go to “Final Tasks” on page 134. If they arestill not correct, go to Step 6.6. Resolder R542 in position (see Figure 9.11). Replace the mainboard and go to “Final Tasks” on page 134.