TM8100 Mobile Radio Service Manual Diagnosis of Faults on Main Board 239
May 2004 © Tait Electronics Limited
Tas k 3 —
Faulty Receiver
If the receiver does not operate, check the operation of the base-band
CODEC and receiver AGC as described below. It is assumed that the
receiver and power-supply circuitry were checked and no faults were
found.
1. Remove the
CDC BOT can. With no RF signal applied, check that
the voltage at pin 14 [at 2N4/2F12] of IC201 exceeds 2.5 V DC
(see Figure 9.32). If it does, go to Step 4. If it does not, go to
Step 2.
2. Check that the voltage at pin 12 [at 2N5/2F11] of IC201 exceeds
1 V DC. If it does, go to Step 3. If it does not, check for and
repair any shorts to ground at the junction of R238 [at 2N5/2F11]
and pin 12 (see Figure 9.32). Confirm the removal of the fault
and return to Subsection 8.1. If the repair failed or the fault could
not be found, return to Subsection 8.1 and replace the complete
main-board assembly.
3. Check the circuitry (R238, R239, R240) [at 2N4/2F11] around
pins 12, 13 and 14 of IC201 (see Figure 9.32). Repair any fault.
Confirm the removal of the fault and return to Subsection 8.1. If
the repair failed or the fault could not be found, return to
Subsection 8.1 and replace the complete main-board assembly.
4. Apply a strong on-channel signal. (Use the programming
application to find the frequency selected for channel 1.) Check
that a sine wave is present at the
QN test point [at 4P1/4C12] (there
is access through a hole in the
IF TOP can — see Figure 9.31). If
there is, the digital board or IC204 is faulty; return to
Subsection 8.1 and replace the complete main-board assembly. If
a sine wave is not present, go to Subsection 9.5 on the receiver.
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