Tait TP9100 - Page 267

TP9100 Service Manual Receiver Fault Finding 267
© Tait Electronics Limited May 2005
Task 18 —
Second IF and
Repair of Matching
Circuitry
If the TCXO is not faulty, check the second IF and, if necessary, repair the
matching circuitry.
1. Input a large unmodulated RF input signal exceeding –90dBm at the
RF connector.
2. Use a needle probe to measure the frequency of the signal at the
QN
test point TP444 (see Figure 12.5). The frequency is the second IF
and should be:
3. If the second IF is correct, go to Step 6. If it is not, go to Step 4.
4. Recalibrate the TCXO.
5. Check if the distortion fault has been removed. If it has, go to “Final
Tasks” on page 134. If it has not, go to Step 6.
6. Remove the
IF IQ BOT can.
7. Check the components between T401 (see Figure 11.4) and IC400
(see Figure 11.1) — these form the matching circuitry for the crystal
filters XF400 and XF401 (see Figure 11.1). Repair any fault.
8. Confirm the removal of the fault, and go to “Final Tasks” on
page 134. If the repair failed or the fault could not be found, replace
the main board and go to “Final Tasks” on page 134.
frequency at QN test point: 64.000kHz