Customer stated that they inadvertently connected the speaker output to a mixer rather than the line output, and claimed it stopped working, no longer any output.
Clean some of the compound away to see the damage (obliteration and vaporisation of the ICs and surrounding tracks).. This one is going to be a challenge:
Ordered replacement ICs (MPS 1019), whilst waiting to arrive, attempted removal and cleanup… Trickier than expected as the welding-action of the failure meant they were quite firmly stuck to the board, what remains:
Managed to start laying down some new copper traces:
The other side not as bad:
After fitting new ICs
With a penny for scale:
Unfortunately there was further damage, the unit was stuck in ‘power-up-mute’, and turns out the signal from the microcontroller wasn’t getting out (the microcontroller I/O port itself was damaged so was not replaceable as had no means to program it), so a bodge was made to permanently leave the unit out of mute.
It meant a little bit of digital noise can be heard during startup if you listened really closely, but otherwise is undetectable during operation.
Calling that one a win! 🙂
Quite why connecting speaker outputs to high impedance input would result in such devastation is a bit strange though, and even if it was producing full output and load disconnected, the catch-diodes should have prevented any nasty voltage spikes from the LC filters?