242
Receiver Fault Finding
TM8100/TM8200 Service Manual
© Tait Electronics Limited
June 2006
10.2
Excessive Loss of Sensitivity
Introduction
This section covers the case where the receiver has suffered an excessive loss
of sensitivity. As measured in
, the receiver gain will be less than 1500,
which implies a sensitivity that is more than 40dBm too low. The fault-
diagnosis procedure for this case consists of five tasks:
■
: check power supplies
■
: check logic signal
■
■
: check biasing of IF amplifier
■
: check matching circuitry
If the fault does not lie with the power supplies, it is probably in the control,
LO, IF1 or IF2 circuitry.
Task 2 —
Check Power
Supplies
First check the two power supplies
3
V
0
AN
and
3
V
0
RX
for the receiver
circuitry.
1.
Remove the board from the chassis.
2.
Check for 3.0V DC (
3
V
0
AN
) at the
TP
601
test point
near the
LO
2
BOT
can (see
3.
If the voltage is correct, go to
. If it is not, the 3V regulator
IC603
is suspect; go to
“Power Supply Fault Finding” on
4.
Remove the
LO
2
BOT
can.
5.
Check for 3.0V DC (
3
V
0
RX
) around the collector feed to
Q402
or
Q403
of LO2 (see
Alternative measurement points are the collector feed to
Q401
of the
RF LNA under the
FE TOP
can (see
) or
Q404
of the IF
amplifier under the
IF
TOP
can (see
).
6.
If the voltage is correct, go to
. If it is not, the 3V RX switch
(based on
Q604
and
Q605
) in the PSU module is suspect; go to
of
“Power Supply Fault Finding” on page 168
TP601 test point: 3.0V DC
Q402 or Q403 collector: 3.0V DC
Summary of Contents for TM8235
Page 1: ...TM8100 mobiles TM8200 mobiles Service Manual MMA 00005 04 Issue 4 June 2006...
Page 10: ...10 TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 62: ...62 Description TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 148: ...148 Disassembly and Reassembly TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 162: ...162 Servicing Procedures TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 178: ...178 Interface Fault Finding TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 258: ...258 Receiver Fault Finding TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 446: ...446 Spare Parts TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
