I have a big trouble now, and I want to get help from you.
I have developed a battery-driven voice amplifier, and just start mass production.
Look at the below pictures.
"A" PCB board works well without noise.
But, "B" PCB board is not working properly.
There are serious noice.
I attached noise mp3 file, please hear it.
The symptoms are:
1. serious noise (hear attached noise.mp3)
2. "SW2" are connected to high (3.3V), the noise become louder. (95% of tested boards.)
3. Some boards are nearly normal, but when "SW2" is connected to high(3.3V), the noise become louder.
4. When earphone volume down, the noise is also decreased.
When volume is 0, noise is 0, that is, no sound from the device.
5. In some boards, when R5 (output of oscillator (12.288MHz)) is decoupled with R & C, noise is reduced.
6. It is likely that all other signals are normal. (MIC bias, earphone output, VDD and ground etc.)
7. Severity of noise varies from board to board.
The circuit and firmware is completely same.
I have tried many things to remove the noise, but I can't fine the cause.........
No suspicious point by visual inspection.
I suspect :
1. PCB faulty (if yes, how to prove?)
2. PCB layout (If PCB design problem, is it possible to fix with above patterns?)
I want to get many advices, your plentiful experiences, helps........
I attached circuits of board.
Please, help me.
I'm looking forward to your help.