The speaker has no sound.
Audio only works with headphones.
The first step is to figure out if the problem is a complete lack of sound or if headphones also work, so try headphones first to see if the audio works.
If you have sound with headphones but not with the speaker, the first step is to try a new speaker.
Diagnosing the audio circuit.
The audio chip receives two signals from resistors R30 and R3 on the CPU; these two points have approximately 1V of voltage when the device is powered on.
The next step is to check if the audio chip is receiving the correct voltage to function.
The next step is to check if the volume potentiometer is working properly. Place the red probe of the multimeter on pin 10 of the chip and move the volume potentiometer; the voltage should change from approximately 0.5 volts to 3 volts.
If audio only works with headphones, the audio jack might be faulty; internal corrosion of this interface is common.
Repair Steps
If the CPU signal is lost, the CPU solder joints might be broken. Inspect the area under a microscope; you might be able to resolder the pins. The traces in the middle of the PCB might also be broken.
If any point on the IC is missing 3V, you can check the battery connector, as this voltage is generated by the battery.
If the voltage at pin 10 is abnormal, the solution is to replace the potentiometer.
If there is corrosion inside the audio jack, clean it as thoroughly as possible, being careful not to damage it, as this component is difficult to find.
If the audio works but the volume is very low, you can replace the capacitor behind the audio jack; that’s a 100uF 4V capacitor.
If the potentiometer pads on your device are damaged, only these pads are needed for repair.
