256
Receiver Fault Finding
TM8100/TM8200 Service Manual
© Tait Electronics Limited
June 2006
10.6
High Receiver Distortion
Introduction
If there is high receiver distortion, the TCXO is suspect, or alternatively, the
matching circuitry for the crystal filters XF400 and XF401. There are two
tasks:
■
: TCXO calibration and repair of TCXO
■
: second IF and repair of matching circuitry
Recalibrating the TCXO might often be sufficient to rectify the fault.
Task 17 —
TCXO Calibration
and Repair of TCXO
First check the TCXO calibration and, if necessary, repair the TCXO.
1.
Use the calibration application to check the TCXO calibration:
Open the
“Raw Data”
page and click the
“Volt Ref/TCXO/VCO/VCXO”
tab.
2.
Note the values listed in the
“Tx TCXO”
and
“Rx TCXO”
fields of the
“TCXO”
group box. The values should be:
3.
If the calibration values are correct, go to
. If they are not,
recalibrate the TCXO and go to
.
4.
Remove the
CDC
TOP
can.
5.
Check the components of the TCXO, which is based on
XL500
(see
). Repair any fault.
6.
Recalibrate the TCXO and check the TCXO calibration values
again as in
and
7.
If the calibration values are now correct, go to
. If they are not,
.
8.
Check if the distortion fault has been removed. If it has, go to
. If it has not, go to
Tx TCXO and Rx TCXO values: b20Hz and –20Hz
Содержание TM8235
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