Chosen Solution
Hello everyone, Computer guy here and repaired all kinds of Apple iMacs… This iMac 27” puzzled me to no end. I’ll do my best to explain… If I powered up the iMac it will shutdown within seconds (it will show the white screen and the Apple chime before shutdown).The iMac won’t come on again unless I unplugged the power cord for few seconds. Try again and the iMac will power up/shutdown within seconds. Yes. I have replaced the power cord.Here is the kicker… after I removed the LCD assembly along with the usual wires/cable/graphic ribbon etc; I can powered up the iMac, hear the Apple chime and it continues to run just fine for hours.As soon as I restored the LCD assembly, the iMac goes back to shutting down within seconds.Could that be the backlight invertor or the main power pack? I am guessing there isn’t enough power? The power pack gets weaker etc? Looking forward to any suggestions you may have. Thank you
If unplugging the display makes a difference then its more likely a short in the T-CON or the backlight LED bar - The display Time to try a second display assembly
