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376 CODEC and Audio Fault Finding TM9100 Service Manual

Task 4 —

Check Audio

Power Amplifier

If there is no fault with the power supplies, check the inputs to the audio PA

as follows. This check is only applicable, however, if the output of the voice-

band CODEC is correct and the signal level varies as the volume is varied.

1. Use the programming application to find the frequency selected for

channel 1.

2. In user mode apply an on-channel RF signal of –47dBm with 60%,

1kHz deviation. The channel must not have signaling enabled.

Set the volume to maximum.

3. Use an oscilloscope probe to check the output of the voice-band

CODEC at the

TP200 test point (see Figure 13.2). The signal

should be:

4. If the above signal is correct, go to Step 5. If it is not, go to Task 7

5. Vary the volume control. This should cause the signal level at the

TP200 test point (see Figure 13.2) to vary. If it does, go to Step 6.

If it does not, go to Task 6

6. Check the voltage at pin 11 of IC202 (see Figure 13.2):

7. If the voltage is correct, go to Step 9. If it is not, check for and repair

any faults in the level-translation circuits incorporating Q200 and

Q201 (see Figure 13.2).

8. Confirm the removal of the fault and go to “Final Tasks” on

page 147. If the repair failed, replace the main-board assembly and go

to “Final Tasks” on page 147.

9. Check the digital signals

DIG AUD PA EN1 at R200 and DIG AUD PA EN2 at

R202 (see Figure 13.2):

10. If the signals are correct, go to Task 5

. If they are not, check the

programming and test set-up; otherwise the digital board is faulty;

replace the main-board assembly and go to “Final Tasks” on

page 147.

TP200 test point: sine wave of 100mV

with 0.6V DC offset

pin 11 of IC202: at least 8V DC

R200 (DIG AUD PA EN1): 3.3V DC

R202 (DIG AUD PA EN2): 0.0V DC

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