Why my iPhone 4s has no more sound and vibrator

Hello,

I'm from France, so please excuse me for my poor English :)

I repair phones and a client brought me an interesting problem. Anything related to sound suddenly stopped working, and the vibrator stopped working at the same time.

When I say anything related to sound, it means speaker, microphone, ear piece, and jack plug.

I spent some time to test it, replaced all the different elements one by one but without any results. I also tried to restore it but nothing changed.

Just during a few seconds, everything worked without apparent reason, but when I tried the vibrator, it vibrated briefly then stopped, and everything was not working again.

I am pretty sure the problem must come from a chip on the motherboard, but I can't identify which one.

I can try any other suggestion.

Thanks,