Motorola A3100 Troubleshooting Manual page 23

• Check if the voltage at Pin 1 of R148 is logic low, if not, check the
audio jack J170 is OK and well-contacted with the main board.
• Using the oscilloscope to see if the waveform is visible at U10 or
U11, if visible at pin 4 but not pin 3, replace U10 or U11 with new
chips.
• If not visible at both pin 4 and pin 3, replace U1 with a new chip.
Service Engineeing & Optimization
Level 3 , Rev.1.0
Earphone Malfunction (1)
J170 Audio Jack