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Hi. I have a late 2012 iMac 27 inch. This morning I tried to turn it on and nothing happened. I removed the screen to see what’s going on. On the logic board, I can see that 1 LED is blinking. When I press the power button the LED resets the blinking but it never stops. I’ve been looking everywhere to determine what this blinking LED mean. PD. It is the only LED on, the other 3 of them are off. Thanks
Well it’s a bad power supply. But not really that bad. It can probably be fixed with just a little work over with a soldering iron. It’s late and I’m going to bed but Google “cold solders” and how to fix them. UPDATE 3/16/16 https://learn.adafruit.com/adafruit-guid… https://www.youtube.com/watch?v=h5_dBMuJ…
Maybe it’s the processor, but I could not test it because it was old …
Have similar problem. I thought it was my i7 cpu, but cpu works perfectly at another machine. I give 12v to motherboard with my bench psu (cooling was off). I found that the led start blinking WHEN i press cpu at the top left (around pin 221). I saw at boardview that this side is for communication with ram. With another cpu i have the same problem. I put a piece of paper to cpu pins to isolate the problem. Even with the ram dimms off, the problem exists. Ram slots seemed perfect. Cpu slot pins seemed perfect. edit: Possible some secondary voltage was short. Found a low resitance (can’t remember how much) at PP3V3_S0 that i didn’t like, i inject 3v to check for hot areas, didn’t found. Then i assemble machine, boot it and works. Tried Apple Service Diagnostics, passed all tests. Hypotheses: It’s magically fixed (temporary or not) It’s something missing (still i didn’t find it) Blow the sd reader slot for dust, i might remove some piece of wire stucked within. I did something without my knowledge that fixed the problem.
i have similar problem, but i have solved it. Power supply is good but logic board have a short. That’s why, system is in a power cycle, so led 1 is blinking. Your system try to boot up, but there is an short on your logic board. check the voltage rails from schematics. S0, S4, S3 and s5 there must be and short.
