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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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After long storage: Fans running, but NO startup chime or display.

My 2017 27" iMac had the logic board replaced just over 12 months ago. It was working fine after that. I moved overseas, and it went into shipping for 3 months. On getting it back about a fortnight ago, it would not start. Where I am currently stationed, there are no Apple Stores or approved Repairers.

SYMPTOMS

  • Power switch works, and fans come on.
  • No startup chime.
  • Nothing on display (remains black).
  • If I power it down by holding power button, it turns off, but then starts back up again after a few seconds. I have to remove power cable immediately it turns off to keep it off.

DIAGNOSTICS

  • I have removed the RAM. If I try to start it up without RAM, it produces the 'no RAM' beep, but symptoms remain the same.
  • I have removed the display screen. LED 1 lights up when power cable is plugged in. LED 2 lights up when I press the power button. Fans run high (as expected with no display). LEDs 3 & 4 do not light up.
  • There does not seem to be any obvious damage or poorly connected cables on the inside, although I have not yet taken off anything other than the display screen.

WAY AHEAD

  • I cannot replace the iMac, nor can I get one shipped to me, due to where I am currently deployed.
  • Is there a PRAM battery in these models that could possibly be drained down after 3 months unplugged? Could that cause the symptoms?
  • Is my only option to get hold of a new logic board and replace? Sadly, that is probably more expensive than the iMac is worth.

Thanks to anyone who has any helpful advice on what to do next.

J

Update (10/12/24)

I thought I would update this question. Unfortunately, it is not good news.

I managed to source a second hand logic board that I was told was working.

I followed the guide, removed my old logic board, and replaced it with a new one. Same SSD, same RAM, same screen, same PSU. On startup, there are exactly the same diagnostics as above. Now, it might be that the 'new' logic board has the same graphics chip problem as my previous one. However, is there anything else that could cause this symptom?

Thanks again for your time.

J

Answer this question I have this problem too

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@torbet are your fans running at normal speed or are they at high speed?

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They are at high speed when the screen is off, but settle down to normal running when I put the screen on.

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@torbet as expected. So that is good. I noticed you have part 2 :-) of this issues posted. It'll be a bit confusing for people.... anyhow new logic board same results with the diagnostic LED's? 1&2 on 3&4 off?

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Yes. Exactly the same issue as before. Down to the iMac restarting after about 10 secs when powered off (holding power button in for 3-5 secs). It made no difference, which means I am statistically unlucky, or there is something else going on. Would a dodgy SSD cause this? My next step is to get an enclosure for the SSD, and check it out as an external drive on another machine.

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@torbet I would at least try and remove those parts that stayed the same. One after the other to try and sort it out.

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It does sound like something is damaged on the Mac, so try some of the steps Apple recommends: if none of these steps work, you will probably have to find some way to repair it. I too live overseas, and I get how frustrating it is when a component brakes with no way to fix it.

https://support.apple.com/en-us/102675

https://support.apple.com/en-us/102623

https://support.apple.com/en-us/102605

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Thank you. I have tried all of those before I took the screen off.

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Hi Torbet,

According to your description, I think your iMac has a VGA problem. However, the VGA of this model is welded on the mainboard, with ordinary users, we can only replace other mainboard.

The order of LED lights is as follows:

1. LED 1: Power Supply.

2. LED 2: Mainboard.

3. LED 3: VGA.

4. LED 4: LCD.

You can also try with the minimum: disconnect all other connections such as HDD, wifi card, speakers. In addition, you should remove RTC Battery on the back of the mainboard and reinstall it after about 2 minutes.

Hope to help you.

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Thank you. I will remove the logic board, which will mean disconnecting everything, and replace the RTC battery. It this changes nothing, I will try and find a replacement logic board.

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torbet will be eternally grateful.
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