Dead iMac and out of ideas- full details in post

[pchc_lx]

Hello, new user here and hoping I could get some suggestions on a really tough hardware problem. Here are the details.

Machine: Apple iMac 21.5-Inch "Core i5" 2.7 (Late 2013) ME086LL/A - iMac14,1 - A1418 - 2638

Synopsis: iMac will not power on after completing several upgrades / part replacements


Original symptoms prompting the upgrade

• iMac works OK, but runs slowly and occasionally “dies”.
• This is an intermittent power / wake problem
• After going to sleep, iMac would be unable to power on.
• No combination of power button / keys would wake or boot iMac
• Only temporary solution: to leave unplugged for an amount of time and try again

Initial repair/upgrade attempt

• Replaced HDD with SSD (with this kit from OWC)
• Repaced 2x4GB RAM w/ 2x8GB RAM (with these RAM sticks)
• Replaced PSU with new PSU (with this new PSU)

(few photos of the process here)

Put everything back together and hit the power button. Nothing.

Machine will not power back on after repairs/replacements.

It booted once, randomly (?!) after indeterminate changes.

I manually shut computer down (*regret doing this*), never started again.

Diagnosis / Troubleshooting attempts

• Replaced HDD with SSD→ Reverted this, old HDD back in
• Repaced 2x4GB RAM w/ 2x8GB RAM→ Reverted this, old RAM back in
• Replaced PSU with new PSU→ Attempted revert, no change, new PSU back in
• Replaced BR2023 mobo Battery w/ new CR2023 (might as well try?)
• Reseated all the above components, plug/unplug, re-seat RAM etc
• Many, many, many combinations of the above

Description of current state

• iMac will not power on nor boot, nor make the boot chime noise
• Screen stays black, does not light up. No beeps. Sometimes I can hear a very faint click sound when pressing the power button.
• Startup key combinations seem to have no effect (difficult to know w/ wireless keyboard though- I’ve tried a mini USB PC keyboard w/ no noticeable effect). This means all the Reset NVRAM/PRAM/SMC processes seem not possible.
• I can force the iMac into a “Fans on High” state by holding power button down while plugging in the IEC cable
• The above implies that the PSU is not dead and the fans at least can power on
• But no other signs of life from the machine whatsoever

I have been working off a mental list of 'things I haven’t tried yet' and going through them one at a time. I’m afraid I am at the end of that list. The only things I can think of

• The motherboard (logic board) is “fried” or dead somehow, I’ve never seen this actually happen to a computer but maybe it does actually happen ?
• I somehow broke something (?) while doing the repairs, I don’t know what it would be, I’ve visually inspected every connecting ribbon cable and component and seen no damage, I experienced no static discharges at any time, I’ve done this before on PCs and Linux computers many times … also annoying that current state is not *thatdifferent from original intermittent issue state
• Some unknown Apple-specific angle that I am unaware of as this is my first time working on an Apple computer. e.g. "you'd never know this unless someone told you but an iMac won't boot unless ___ (tiny thing easily missed)"

I’m at the point where I think I just have to bring it into a computer repair service, as I think this may be beyond me. Frustrating situation.

If there is anything else I can try here I would love to know, thanks in advance

 

[harryb2448]

Amongst your tests, did you check if the LED lights are all (4) functioning? If these are not functioning you may be in for a logic board replacement. Have a read of this from ifixit:-

No power on, No LED on logic board - iMac Intel 21.5" EMC 2638

Hey guys, Today I need your help! I have an iMac late 2013 with 11.7 Volt of Logicboard (J600 plug) . No diagnostic LEDs. System no Start I still have to measure other small plugs. does one have a tip? O_o. System : iMac A1418 (21.5 Zoll) ME087D/A (late, 2013) i5 4570 ,NVIDIA 750M , 8 GB Ram...

www.ifixit.com

 

[chscag]

Welcome to our forums.

I saw your same post in another forum. It appears you've done a considerable amount of work and troubleshooting. Unfortunately, I don't have any ideas that may help you.

We do have a certified Apple tech as a member of our forums who drops in now and then. If he reads your post he may have some ideas that might help.

You might want to wait before taking it to a computer repair service. Also, it might not be a good idea to spend more money on a machine that is going on 8 years old. Just my opinion.

 

[pchc_lx]

Amongst your tests, did you check if the LED lights are all (4) functioning? If these are not functioning you may be in for a logic board replacement. nHave a read of this from ifixit:-

Thanks harryb2448 I had seen some reference to LED diagnostics here and there but haven't properly looked into it. I'll try to find the corresponding codes for my model and see if any new info can be found.

Welcome to our forums.

I saw your same post in another forum. It appears you've done a considerable amount of work and troubleshooting. Unfortunately, I don't have any ideas that may help you.

We do have a certified Apple tech as a member of our forums who drops in now and then. If he reads your post he may have some ideas that might help.

You might want to wait before taking it to a computer repair service. Also, it might not be a good idea to spend more money on a machine that is going on 8 years old. Just my opinion.

Thanks chscag, sorry to crosspost a few forums (a little desperate here haha).
I think you make a good point about money sink considering the age of the machine. I hadn't really weighed that angle and am going to do some pricing out of other models and see what makes the most sense considering.