M12 Funky Power Switch

[MartinD]

I just followed Chips video and replaced my power switch (thanks a million Chip).
Unit powers up perfectly now.

However no input signal on connecting microphone to channel 1 (tested that microphone works)
or any other channel. Nothing showing on input meters when I speak into microphone either.
Then I connect output monitor, switch T12 off an on .
Squealing noise that goes from low to high pitched and deafening

So bummed, I thought I'd fixed the only issue, the power switch.
Not sure what to do next! ?

 

[Max Relic]

Next warmly recommended step is contacting Tascam support, your unit must be analyzed by competent technical service.