iMac 4K 2017 booting to black screen

[viken]

Hi,

As I can't bring my iMac to an apple center (all shops are closed around me because of covid), I'd like to ask for your help about the issue I'm facing.

The iMac suddenly start booting to black screen or weird screens, I tried to boot on bootcamp and get weird things to. The iMac boot on safe mode though and it works.

I'm afraid this could be the GPU, because I think I'd have to replace all the motherboard and the price I saw on ebay are so expensive :/

Any advices for me ?

Thanks for your help !

 

[Applicator]

Yepp, that's definitely a broken GPU. I'm having similar trouble with my wife's iMac 4k 2017, too. Her iMac works fine until set to sleep. Now it's running on "amphetamin" 24/7. It's up for 3 days and no crash so far.
I'm just hoping it lasts until Mx-iMacs are available, or a repair shop offers Radeon Pro replacements.

What I found during my research: https://discussions.apple.com/thread/7781774
It's like using safe mode only for the graphics. This is what I will try, when our iMac issue gets worse.

I think we can't count on Apple for a service or repair program, even tough I've seen a couple of broken Radeon Pros in MBPs as well.

 

[viken]

Yepp, that's definitely a broken GPU. I'm having similar trouble with my wife's iMac 4k 2017, too. Her iMac works fine until set to sleep. Now it's running on "amphetamin" 24/7. It's up for 3 days and no crash so far.
I'm just hoping it lasts until Mx-iMacs are available, or a repair shop offers Radeon Pro replacements.

What I found during my research: https://discussions.apple.com/thread/7781774
It's like using safe mode only for the graphics. This is what I will try, when our iMac issue gets worse.

I think we can't count on Apple for a service or repair program, even tough I've seen a couple of broken Radeon Pros in MBPs as well.

Thanks for your feedback.

I let my iMac sit for 24hours and now it crashes 4-5 times and then the 5-6 times i try to boot it actually works.

I got the result of the kernel panic which starts with :

panic(cpu 0 caller 0xffffff7fbbfb115b): "virtual bool IOAccelLegacyDisplayMachine::display_mode_did_change(uint32_t): AMDRadeonAccelerator driver returns false"@/AppleInternal/BuildRoot/Library/Caches/com.apple.xbs/Sources/IOAcceleratorFamily_kexts/IOAcceleratorFamily-439.35.4/Kext2/IOAccelLegacyDisplayMachine.cpp:267

It does point to the GPU... but I don't understand how it can sometime boot and work perfectly (I can even play video games without problems), and then I stop and restart it the next day and it crashes...

I saw the trick you mentioned, if it eventually never boot again I will try it too, thanks

I'm scared Apple tells me to pay for a new GPU though, I've read there was replacement program for some iMac but my model is unfortunately not one of those...

Anyway with the current situation Apple store are closed in my town so all I can do is cross my fingers so it keeps working after 5-6 try of boot everyday 🥲