284 CODEC and Audio Fault Finding TP9100 Service Manual
© Tait Electronics Limited May 2005
12.5 Faulty Modulation
Introduction This section covers the case where the radio transmits the correct amount of
RF power, but there is either no modulation or the modulation is distorted.
There are four tasks:
■ Task 11: check internal microphone
■ Task 12: initial checks of external microphone
■ Task 13: check external microphone audio
■ Task 14: check external microphone bias
Task 11 —
Check Internal
Microphone
To check the modulation from the internal microphone:
1. Remove any external microphone or accessory and apply an audio
acoustic signal from an external speaker or noise source near the
internal speaker.
2. Enter the CCTM command 33 to place the radio in transmit mode
(the frequency is that of channel 1). The radio must be in transmit
mode for the +5
VTX and microphone pre-amp circuit to operate.
3. Create an audio signal by whistling into the speaker and check that
the audio signal appears at the junction of C235 and R261, and also
the junction of C236 and R262 (see Figure 12.3).
4. If the audio signal is not present check and repair the speaker, speaker
pins, components and soldering of C235 and C236
(see Figure 12.3). If the signal is present, go to Step 6.
5. 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.
6. Create an audio signal by whistling into the speaker and check that
the audio signal appears at the junction of R267 and IC202
(see Figure 12.3).
7. Enter the CCTM command 32 to place the radio in receive mode.
8. If the audio signal is present, go to “Frequency Synthesizer
Fault Finding” on page 159 on the frequency synthesizer fault
finding. If it is not, go to Step 9.
9. Check the components and soldering around IC202 and repair or
replace as required.
10. 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.
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