2019 27" iMac Randomly Shuts Down!

[RedSoxSue]

I purchased a 2019 27" iMac with a Pro Vega 48 8g graphics card and 128g of RAM (3rd party that I installed). I bought it in May of this year and started having issues with it in October. I would be editing in Premiere Pro and it would just randomly shut down. It only shuts down while editing video in either Premiere Pro or Final Cut. I can do anything else and i'm fine. When it shuts down, I have to unplug from the power source and plug back in. In early November I brought it to an Apple Store where they erased everything and installed Big Sur. I felt that no diagnostics were done at all. It worked for a month and just started doing the same thing. I'm thinking it's either the graphics card or power supply. I'm also wondering if the 3rd party RAM has anything to do with it. I've been researching this issue and it seems to be a common problem with iMacs from way back. What's up with that??? I have seen a lot of these issues get fixed with a new power supply...but some are logic board as well. I have another appointment with a "Genius" from Apple tommorow...I shelled out 4k for this machine, so far I am not impressed. My 2012 Mac Mini was more reliable than this thing. UGH!

 

[barbu]

based on your description, it sounds like a bum power supply. It happens, sadly (the iMac G5 PSUs would always fail, but that was due to a very specific bit of electrolytic piracy that affected a bunch of innocent companies).
You have AppleCare so it will be annoying to have it repaired, but it will at least be covered.
The RAM will have nothing to do with it, but if you want to be extra careful, you can remove it before taking it in. Just make sure to be polite but firm. Do not tell them you think the PSU is bad, just describe the symptoms and see what they say. It doesn't hurt to remind them that you've already brought it in once and how it's messing up your work, etc. Just keep cool, don't lay it on too thick. It should not take much convincing to get a new PSU.

 

[barbu]

if it makes you feel any better, both my 2008 and 2013 imacs have worked all these years without fault.

 

[TwoH]

This sounds more like an issue with your third-party RAM more than PSU/GPU. Especially when it is only happening on certain programs.

 

[PBG4 Dude]

based on your description, it sounds like a bum power supply. It happens, sadly (the iMac G5 PSUs would always fail, but that was due to a very specific bit of electrolytic piracy that affected a bunch of innocent companies).
You have AppleCare so it will be annoying to have it repaired, but it will at least be covered.
The RAM will have nothing to do with it, but if you want to be extra careful, you can remove it before taking it in. Just make sure to be polite but firm. Do not tell them you think the PSU is bad, just describe the symptoms and see what they say. It doesn't hurt to remind them that you've already brought it in once and how it's messing up your work, etc. Just keep cool, don't lay it on too thick. It should not take much convincing to get a new PSU.

Oh man, I was burnt by the bad caps in my rev A iMac G5.
The whole Nichicon espionage situation sounded like a Raiders of the Lost Ark style screwup. They only got half the electrolyte formula, just like the bad guy only got half of the instructions on how tall to make the staff in Raiders.

I think www.badcaps.net is still active for people wanting the history of this amazing cockup.

 

[Fishrrman]

Did you keep the original RAM?
If so, I would suggest that you REMOVE the 3rd-party RAM, and re-install the original RAM in place.
(Yes, I realize it may constrain you using a smaller amount of RAM for a day or two)

Run like this for 2-3 days.
Do the shutdowns disappear, or do they persist?

 

[Albert2011]

I had the same problem with my 2019 27" iMac. The iMac came with 2 original 4 GB Apple installed RAM cards. I added 2 OWC 8 GB RAM cards. Removing the 2 Apple installed RAM cards fixed the problem. FYI - my unit has a 1 TB SSD drive NOT a fusion drive. It has been failing! Ugh. I now use and boot from an external Thunderbolt SSD.

 

[Nicole1980]

Definitely try different ram (or removing select ram sticks) and see if that solves it first.