Late 2012 27" iMac shutting down now won't power on

[timeshifter]

Customer has a Late 2012 27” iMac. A few times in recent days / weeks they’ve found it shut off. Doesn’t happen while they’re using it. Sometimes it won’t power on without unplugging and plugging back in (SMC reset). Today while I was there it finally bit the dust and won’t power on at all.

I’m thinking (hoping) power supply. Problem is a) I only see aftermarket power supplies for sale on Amazon, none on iFixit and b) I’ve never opened the new thin iMacs, but I guess there’s no time like the present.

They know they’ll be down for a few days and can wait, I’ve got the machine in my car now. They’re considering buying a new machine. But if they decide to fix for this user, fix to hand down to someone else, or scrap it (and I’ll try to fix as a resell), … I still need to attempt a repair.

So, anyone else seen power problems with this model? How like could it be the motherboard or something that is not the power supply?

I’ll probably order iFixit’s repair tools and this power supply from Amazon.

Any feedback?

 

[cyabro]

Without getting it open and seeing the diagnostic LEDs on the mainboard, you won't know for sure if it's the PSU or something else.

 

[trevm999]

I can't remember if I ever did a PSU replacement on one of the thin iMacs, but with the regular iMacs, I can only remember once when it wasn't a PSU replacement. I always did check things out with a pen voltage checker though, but even if voltage is getting the the logic board, that's doesn't actually prove too much.

The official Apple steps would be to check the diagnostic LEDs, check the cables, then swap out the PSU.

 

[timeshifter]

The official Apple steps would be to check the diagnostic LEDs, check the cables, then swap out the PSU.

Did some digging around, is this accurate for the LEDs?

https://www.ifixit.com/Answers/View...+diagnostic+led's+on+this+model's+logic+board

 

[cyabro]

Did some digging around, is this accurate for the LEDs?

https://www.ifixit.com/Answers/View/126233/Where+are+the+diagnostic+led's+on+this+model's+logic+board

Not in our Apple system right now but that sounds right.

I had one just last week that wouldn’t power on.
After opening it and seeing not even led #1 on thought it must be psu.
However even a new psu had the exact same issue so looks like a faulty main board.