オリジナル投稿者： Larry Jorgenson ,
Found this thread troubleshooting a similar problem. iMac would not turn on one day. Power Supply is providing voltage to the logic board - LED 1 is lit (very difficult to see on the very first 2009 21.5 iMac model but I get voltage at pins 1 and 4 on the logic board). After reading this thread I pulled the RAM (as a side not this iMac and the RAM compartment were very dusty and full of fuzz which I blew out after pulling the RAM). The iMac did power on although there was no chime and no error beeps (note that the display was not installed). Just fans on high. I turned it off and turned it back on several times and got the same result each time. When I tried reinstalling the RAM one by one I would get nothing. Thinking the RAM or slots were bad I tried once more to power the machine with no RAM and I am back to a no power situation again. I have not checked the PRAM battery - for some reason Apple put it on the back side of the logic board which means a complete disassembly just to check it. Or, does anyone know any way to check the PRAM voltage without exposing the actual battery? Are the pins accessible from the front? Anyone with any other ideas - I’m all ears.