396
CODEC and Audio Fault Finding
TM8100/TM8200 Service Manual
© Tait Electronics Limited
June 2006
13.4
Faulty Receiver
Introduction
This section covers the case where the receiver does not operate, although
there is no apparent fault in the receiver circuit itself. There are two tasks:
■
: check level shifter
■
QN
test point
The latter check will isolate the module at fault if the level shifter is not the
cause of the problem.
Task 10 —
Check Level Shifter
Check the operation of the base-band CODEC and receiver AGC as
described below. This concerns the level-shifter circuit. It is assumed that the
receiver and power-supply circuitry were checked and no faults were found.
1.
If not already done, remove the
CDC
BOT
can.
2.
With no RF signal applied, check the voltage at pin 14 of
IC201
(see
3.
If the above voltage is correct, go to
. If it is not, go to
4.
Check the voltage at pin 12 of
IC201
(see
):
5.
If the above voltage is correct, go to
. If it is not, go to
6.
Check for and repair any shorts to ground at the junction of
R238
and pin 12 of
IC201
(see
7.
Confirm the removal of the fault and go to
. If the repair failed or the fault could not be found, replace
the board and go to
8.
Check the circuitry (
R238
,
R239
,
R240
) around pins 12, 13 and 14
of
IC201
(see
). Repair any fault.
9.
Confirm the removal of the fault and go to
. If the repair failed or the fault could not be found, replace
the board and go to
pin 14 of IC201: more than 2.5V DC
pin 12 of IC201: more than 1V 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...