244 Diagnosis of Faults on Main Board TM8100 Mobile Radio Service Manual
May 2004 © Tait Electronics Limited
Task 6 —
Faulty Modulation
Using Auxiliary
Connector
If the transmitter operates normally but there is no modulation (although
there is modulation at the auxiliary connector), proceed as follows:
1. Enter the CCTM command 33 to place the radio in transmit
mode. (The frequency is that of channel 1.) Check the
modulation via the microphone input. If it is correct, go to Step
2. If it is not, go to Task 4.
2. Apply a 1 kHz AC-coupled signal of 0.7 V
pp
at pin 7 (AUD TAP IN)
of the auxiliary connector (alternatively, as
ITF AUD TAP IN [at
2M2/2D11] at the junction of R237 and R241 — see
Figure 9.31). Enter the CCTM command 323 t5. Check that the
DC offset voltage at pin 7 is approximately 1.5 V DC. If it is, go
to Step 3. If it is not, go to Step 4.
3. Remove the
CDC TOP can. Check for and repair any soldering
faults around IC205 [at 2P2/2D12], or else replace IC205 (see
Figure 9.31). Confirm the removal of the fault and return to
Subsection 8.1. If the repair failed, return to Subsection 8.1 and
replace the complete main-board assembly.
4. Check that there are no shorts at pin 7 of the auxiliary connector.
If there are none, go to Step 5. If there are, repair the fault.
Confirm the removal of the fault and return to Subsection 8.1. If
the repair failed, return to Subsection 8.1 and replace the
complete main-board assembly.
5. Remove the
CDC TOP can. Check that the voltage at both ends of
R241 [at 2P2/2D12] is 1.5 V DC (see Figure 9.31). If it is, go to
Step 6. If it is not OK, go to Step 7.
6. Check for and repair any soldering faults around IC205 [at
2P2/2D12], or else replace IC205 (see Figure 9.31). Confirm the
removal of the fault and return to Subsection 8.1. If the repair
failed, return to Subsection 8.1 and replace the complete main-
board assembly.
7. Remove R241 and check that the voltage at pin 3 of IC205 is
1.5 V DC (see Figure 9.31). If it is, go to Step 8. If it is not,
return to Subsection 8.1 and replace the complete main-board
assembly.
8. Check for and repair any soldering faults around R241 and IC205
[at 2P2/2D12] (see Figure 9.31). Confirm the removal of the
fault and return to Subsection 8.1. If the repair failed, return to
Subsection 8.1 and replace the complete main-board assembly.
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