TM8100/TM8200 Service Manual
Receiver Fault Finding
257
© Tait Electronics Limited
June 2006
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
— access is through the hole in the
IF TOP
can
(see
). The frequency is the second IF and should be:
3.
If the second IF is correct, go to
4.
Recalibrate the TCXO.
5.
Check if the distortion fault has been removed. If it has, go to
.
6.
Remove the
IF TOP
can.
7.
Check the components between
T401
and
IC400
— these form the
matching circuitry for the crystal filters
XF400
and
XF401
(see
8.
Repair any fault, confirm the removal of the fault, and go to
. If the repair failed or no fault could be found,
replace the board and go to
.
frequency at
QN
test point: 64.000kHz
Содержание TM8235
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