2017 iMac: Doesn’t boot, only USB power

[BShanks]

Hello,

I own a 2017 21.5” 4K iMac. Last year, I upgraded RAM to 32GB and HDD->SSD and am on Big Sur.

Overall, works fine, but with a kernel panic once every 2 months. Still, everything goes back to normal.

Was browsing the web this morning with a sudden shutdown. Error message said a kernel panic. Restarted with a fresh instance. Starting browsing again and sudden everything froze and shutdown.

However, nothing has worked to get the iMac up again (SMC/NVRAM) and this has never happened before.

What works:
- Any USB peripheral turns on
- High speed fan trick (plug power in while turning on)

What doesn’t:
- Everything else. Not even sure keyboard is getting connected as CAPS LOCK light doesn’t turn on, so maybe that is why NVRAM can’t be reset?

Any ideas? I guess my only hope is to open up the iMac and check the diagnostic lights and perhaps remove the RAM and change the small battery?

 

[StoneJack]

Mainboard or cpu, gpu defective. Check YouTube videos for hints

 

[BShanks]

Will do. Thanks. Seems like any of those issues wouldn’t be worth the cost to fix.

 

[Fishrrman]

Before you go pulling out the motherboard, I suggest you REMOVE the 3rd-party RAM you installed.

Put the factory RAM back in.

Does this change anything?

 

[BShanks]

Before you go pulling out the motherboard, I suggest you REMOVE the 3rd-party RAM you installed.

Put the factory RAM back in.

Does this change anything?

This is the plan and I will do so this weekend. Finger’s crossed!

I guess I find it curious that the system accepted the RAM i added and threw up no errors via any diagnostics. It did work well with the replacement RAM, but perhaps it was all leading up to this eventuality.

 

[BShanks]

Well Mr. Fishrrman, your advice was sound! I opened up my iMac and sure enough, only 2 diagnostic LEDs were lit. Once I removed the "upgraded" ram and replaced with my original 8GB, the other diagnostic LEDs lit up and my iMac was back to being operational! *phew*

I thought I did my due-diligence when purchasing replacement RAM, and while all the specs seem to match what I needed, in hindsight, the upgraded RAM, while it did work for nearly a year, was beset with problems, culminating in total failure. Can this be attributed to failing RAM, or did something not match? All I can think of is that the upgraded RAM is dual-rank vs the original single-rank?

This is what I purchased: Timetec 32GB KIT(2x16GB) Compatible for Apple 2017 iMac

Back to the drawing board! Thanks again!

 

[Fishrrman]

For future RAM, I'd highly recommend these guys:

iMac Memory Upgrades

DMS Certified Memory for all iMacs, including Intel Core i3, i5, i7 models. 100% Apple Compatible & backed by a Lifetime Warranty. Free shipping available.

www.datamemorysystems.com

 

[BShanks]

Thanks for the recommendation, I've never heard of DMS. I was leaning toward OWC or Crucial (Mac versions), but I will take a look!