Faulty Receiver - Tait TM8235 Service Manual

13.4

Faulty Receiver

Introduction
Task 10 —
Check Level Shifter
396 CODEC and Audio Fault Finding
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:
Task 10: check level shifter
Task 11: check
QN
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
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
2. 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
3. If the above voltage is correct, go to
4. Check the voltage at pin 12 of IC201 (see
pin 12 of IC201: more than 1V DC
5. If the above voltage is correct, 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
page 157. 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 Figure
9. Confirm the removal of the fault and go to
page 157. If the repair failed or the fault could not be found, replace
the board and go to
test point
CDC BOT
Task
Step
Figure 13.7).
"Final Tasks" on page
13.7). Repair any fault.
"Final Tasks" on page
can.
11. If it is not, go to Step
Figure 13.7):
8. If it is not, go to Step
"Final Tasks" on
157.
"Final Tasks" on
157.
TM8100/TM8200 Service Manual
© Tait Electronics Limited June 2006
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