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Model A1419 / EMC 2806 / Late 2014 or Mid 2015. 3.3 or 3.5 GHz Core i5 or 4.0 GHz Core i7 (ID iMac15,1); EMC 2834 late 2015 / 3.3 or 3.5 GHz Core i5 or 4.0 GHz Core i7 (iMac17,1) All with Retina 5K displays

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iMac not turning on, Service LED#1 blinking

Hi,

would appreciate any comment/help about the following issue:

I got an iMac 27“, Late 2015, CTO. Display had a transport damage. Removed screen and tried to power on, service LED#1 is only blinking, if I press the power Button for a longer time, sometimes the LED will just stay on, sometimes the LED continues to blink. I can hear some strange noises from the PSU… Did anyone experience a challenge like this, should I try another PSU or could this be related to a faulty logic board? Could a faulty CPU be the reason for such a behavior?

Appreciate any support,

thanks,

marcus

Update (06/12/2019)

Hi,

just swapped the PSU against a known good one, same result, please see the video:

I guess it is Logic Board related, could this be a faulty CPU?

Service LED#1 is blinking, Service LED#2 is frequently and very briefly flashing (almost unnoticeable)

Any ideas?

Regards,

Marcus

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Any update to this problem? I have an early 2009 machine with the same symptoms. I do not have a new power supply to test but I understand you tried a new PSU on yours and it made no difference. Please provide an update if you have more information to share.

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Hi Larry, yes, I have exchanged the PSU against a known working one, as this ended up in the same result, I assumed that the CPU might stopped working. Also exchanged the CPU against a known working one, same result, so I give up now. My last try would be to replace the GPU, and maybe this will be a safe bet that this will be the faulty part, but as the GPU is soldered to the board, I do not have the required machinery/tools to do so, will now replace the whole board.

Regards,

Marcus

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@macmarcus Boo. In my case, I don't think the machine is worth the effort to repair. Good thing I only spent $20 buying it. One difference I note between mine and yours (based on the video), my LED is flashing probably twice as fast. Yours is a slow flash. Does the speed of the flash indicate any different problem?

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@macmarcus @larry767 - You both have bad logic boards. The GPU's in this series is soldered to the logic board directly. It does not have an MXM card unlike the older 2011 and back models

Power surges or a lightning strike likely killed both the power supply and the logic board power logic VRM's.

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Hey Dan, thank you for the comment. Does this mean a replacement of the GPU would do it or would you need to replace the LBP logic VRMs, which I would think is not doable?

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I would start off replacing the Power Supply. There might be more damage…

iMac Intel 27" Retina 5K Display Power Supply Replacement

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The LED is telling you no power to the Logic board.

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Thank you Dan and mayer, will start with a replacement PSU and will post the results

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Sorry you got a double whammy! Your system got a power surge or a lightning strike, killed both the power supply and the logic board.

Before you use the outlet again make sure its properly wired and grounded and make sure your buildings grounding is in good shape (breaker panels ground). You do want to use surge suppressors on all of your grear (anything that plugs to your system) printers, scanners HD's and all of the Ethernet gear. I do recommend using a UPS for your system directly.

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I was surprised the PSU was not the fault.

Next, let’s take a look at the RAM. First we need to verify if it is the correct RAM for your machine, please pull it and tell us what you have.

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Hi mayer,

the RAM is not the problem, the iMac don't even act different with or without any RAM installed, I don't even hear the sound that normally appears if RAM is missing. However, I am using CRUCIAL CT8G3S186DM.M16FP, so 2x 8 GB, which is recommended for this machine.

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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.

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