TM8100/TM8200 Service Manual
Receiver Fault Finding
245
© Tait Electronics Limited
June 2006
Task 5 —
Check Biasing
of IF Amplifier
If the lock status is normal, check the biasing of the IF amplifier.
1.
Remove the
IF
TOP
can.
2.
Check all components around
Q404
of the IF amplifier
(see
3.
Check the 3V supply voltage at
L419
; use the measurement point
shown in
4.
Also check the amplifier bias conditions. First measure V
c
between
the collector of
Q404
and ground (see
5.
Secondly, check I
c
. To do so, unsolder and raise one terminal of
L419
(tombstone position) (see
), connect a multimeter
between this terminal and the pad for the terminal, and measure the
current.
6.
If the checks in
. If there
is a fault, repair it and go to
7.
Recalibrate the receiver using the calibration application.
8.
Confirm the removal of the fault, and go to
. If the repair failed go to
Task 6 —
Check Matching
Circuitry
Having excluded the IF amplifier, check the matching circuitry for the
crystal filters.
1.
Check all remaining components between
T401
and
IC400
— these
form the matching circuitry for the crystal filters
XF400
and
XF401
(see
2.
If the above check reveals no fault, go to
. If there is a fault,
3.
Remove the
PIN
TOP
and
LPF
TOP
cans.
4.
Make a visual check of the components in the receive path of the PIN
switch and LPF circuits.
5.
If the visual check reveals an obvious fault, repair it and go to
If there is no obvious fault, go to
6.
Recalibrate the receiver using the calibration application.
7.
Confirm the removal of the fault, and go to
. If the repair failed go to
V
c
: 2.0 ± 0.2V
I
c
: 1.8 ± 0.5mA
Содержание TM8235
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