Hi check your -12v Signal comes in from the back of the mother through a via just above the first amp between amp and thats u404(amp) and c443 there is a via which supplies the amp the -12v Signal if the via is damaged due the the c443 leaking it will be damage it and will not suppy the amp with the -12v siganl. or the -12v line under u404 is damage. I Had the same Problem and this is what caused it in my case.
Regards Laurence
