Imac late 2012 booting problem

[dqtech]

sometimes it can boot normally and sometimes cant turn on at all...i actually dont know where to start for diagnos...already replace power supply but problem still persist....i check power button with buzzer and it still in good condition...when cannot turn on, only 1LED shows....i try using tweezer to jumper power button but also not working....need to rest imac for about 2-3 hours then it will boot normally

here i attach schematic and boardview

[Moxado]

Re: Imac late 2012 booting problem

you should try first with a new psu