Tait TP9100, Service Manual, Page: 282 / 326

282 CODEC and Audio Fault Finding
TP9100 Service Manual
© Tait Electronics Limited May 2005
12.4 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:
■
Task 9: check level shifter
■
Task 10: check
QN
signal
The latter check will isolate the module at fault if the level shifter is not the
cause of the problem.
Task 9 —
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 and in receive mode, check the voltage at
pin 14 of
IC201 (see Figure 12.5 ):
3. If the above voltage is correct, go to Task 10 . If it is not, go to Step 4 .
4. Check the voltage at pin 12 of IC201 (see Figure 12.5 ):
5. If the above voltage is correct, go to Step 8 . If it is not, go to Step 6 .
6. Check for and repair any shorts to ground at the junction of R238
and pin 12 of IC201 (see Figure 12.5 ).
7. Confirm the removal of the fault and go to “Final Tasks” on
page 134 . If the repair failed or the fault could not be found, replace
the main board go to “Final Tasks” on page 134 .
8. Check the circuitry ( R238 , R239 , R240 ) around pins 12, 13 and 14
of IC201 (see Figure 12.5 ). Repair any fault.
9. Confirm the removal of the fault and go to “Final Tasks” on
page 134 . If the repair failed or the fault could not be found, replace
the main board and go to “Final Tasks” on page 134 .
pin 14 of IC201: more than 2.5V DC
pin 12 of IC201: more than 1V DC