Faulty Receiver; Check Level Shifter - Tait TM9100 Service Manual

13.4

Faulty Receiver

This section covers the case where the receiver does not operate, although
Introduction
there is no apparent fault in the receiver circuit itself. There are two tasks:
The latter check will isolate the module at fault if the level shifter is not the
cause of the problem.
Check the operation of the base-band CODEC and receiver AGC as
Task 10 —

Check Level Shifter

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.
2.
3.
4.
5.
6.
7.
8.
9.
TM9100 Service Manual
© Tait Electronics Limited August 2005
Task 10: check level shifter
Task 11: check test point
QN
If not already done, remove the
With no RF signal applied, check the voltage at pin 14 of IC201
(see Figure 13.7):
pin 14 of IC201: more than 2.5V DC
If the above voltage is correct, go to
Check the voltage at pin 12 of IC201 (see
pin 12 of IC201: more than 1V DC
If the above voltage is correct, go to
Check for and repair any shorts to ground at the junction of R238
and pin 12 of IC201 (see
Confirm the removal of the fault and go to
page 147. If the repair failed or the fault could not be found, replace
the main-board assembly and go to
Check the circuitry (R238, R239, R240) around pins 12, 13 and 14
of IC201 (see Figure
Confirm the removal of the fault and go to
page 147. If the repair failed or the fault could not be found, replace
the main-board assembly and go to
can.
CDC BOT
Task 11. If it is not, go to
Figure
Step 8. If it is not, go to
Figure 13.7).
"Final Tasks" on
"Final Tasks" on page
13.7). Repair any fault.
"Final Tasks" on
"Final Tasks" on page
CODEC and Audio Fault Finding
Step 4.
13.7):
Step 6.
147.
147.
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