iMac27 A1312 No signs of life, led 1 blinks twice.

[Bentley100]

Hi, I got this iMac to fix and I have been having a really hard time. When I plug it in led 1 blinks twice but never fully turns on, it only does this when I plug it in then it imminently stops. The PSU does make a slight buzzing noise but nothing noticeable. I have replaced the PSU with a newly bought one from eBay. I have already also tried different RAM. Here is a video of what happens when i plug it in.

 

[The_Croupier]

Disconnect all hardware devices, I would start with the gpu.
And I must say that is a terrible video not really helping at all to diagnose.

 

[Bentley100]

Sorry about that video, I was just trying to show off Led 1 blinking but had terrible lighting. I have disconnected everything but still no luck, should I take the GPU out and test without it?

 

[The_Croupier]

Yes, gpu is number hardware issue in old iMacs.

 

[Bentley100]

i have narrowed it down to the eBay seller selling me a faulty PSU. I did take the graphics card out but there was still no difference. currently working on refunding the PSU and getting a new one. I will update you when i get another psu.

 

[w.sanjaya83]

Hi.. I think we have same issue. Mine 27" 2011 iMac just got GPU Card in and out for several times, then it completely dead. Only the first LED blink at once, then its off; no signs of life.

But just now I'm curious about something after digging some information. I found out then CPU if unplug, the first LED turned on. But when I put it back, the first LED shuts off again.

It seems like I dont tell the whole story how it become like that. But maybe my comments give you a hint. It might be dead processor, or some short around the CPU area. Hope it helps.

 

[slomat]

Hi, I have the same behaviour of the diagnostic LEDs on my imac.

i have narrowed it down to the eBay seller selling me a faulty PSU. I did take the graphics card out but there was still no difference. currently working on refunding the PSU and getting a new one. I will update you when i get another psu.

@Bentley100, did changing the PSU solve the problem in the end?

 

[Nguyen Duc Hieu]

Hi, I have the same behaviour of the diagnostic LEDs on my imac.


@Bentley100, did changing the PSU solve the problem in the end?

Best case scenario: The GPU failed and caused a short circuit.
Worst case scenario (what happened to me): The whole thing was toasted (PSU, logicboard, GPU). I struggled to save the only thing left not broken: The LCD panel and its aluminum frame....

 

[slomat]

Best case scenario: The GPU failed and caused a short circuit.
Worst case scenario (what happened to me): The whole thing was toasted (PSU, logicboard, GPU). I struggled to save the only thing left not broken: The LCD panel and its aluminum frame....

How did you diagnose that these 3 components were toasted? I don't have any apparent short circuit symptoms on the PSU or the GPU (I need to look at the logic board).

 

[Nguyen Duc Hieu]

How did you diagnose that these 3 components were toasted? I don't have any apparent short circuit symptoms on the PSU or the GPU (I need to look at the logic board).

I diagnosed them by swapping the PSU from a working iMac 2011 and remove the GPU, which was assumed to be dead right from the beginning and of no use to me even if it's working.
Good PSU in bad iMac 2011: Still dead, 1st led blinked twice and got dimmed.
Bad PSU in good iMac 2011: dimmed 1st led

My initial intention was not to rescue the PC parts, but the LCD panel so I didn't test further.