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iMac starts up with black screen.

Hello,

My 2017 iMac 21.5” 4K does not show pictures on display any more.

It powers up with the chime but shows nothing on the display. It is not a backlight issue. NVRAM clear and SMC reset were tried but no luck.

I can login remotely using ssh. If I try screen share, it only shows black desktop on a remote computer.

An external display does not show pictures either. But I am not sure if the USB-C to HDMI dongle is recognized.

I opened it up to see the diagnostic LEDs and I see that 3 LEDs are lit. I replaced the button battery with a new one but no luck. I also replaced thermal paste on the CPU, GPU and VRAM but no change (which is expected).

So my question is that is there any way to run hardware diagnostics remotely? If not, what’s the next move I should take?

Thanks,

Tatsuya Minami

Отвечено! Посмотреть ответ У меня та же проблема

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I have an update on this iMac.

I bought an IR reflow machine from Amazon.

https://www.amazon.com/gp/product/B08R3P...

And reflowed the GPU and the VRAMs. I followed the procedure in these videos.

https://youtu.be/j67Z9D0rs5s

https://youtu.be/UOoR27IF7Jk

After the reflow, my iMac started up with a picture on display!

Hope this information helps some one who's having the same problem.

Tatsuya Minami

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Sadly you’ve already got the needed info. If an external display won’t work as well then the issue is within the logic board GPU logic.

Using any remote desktop service (SSH in this case) doesn’t use the systems GPU which is why it worked!

This could be a simple issue or it could be a blown GPU chip which would require a new logic board. You’ll need to find someone with the very deep skills to fix your logic board or you could just replace it.

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Thank you, Dan.

This used to be an intermittent problem but now it's a permanent one. Probably there's a solder crack or alike somewhere.

For the people who have the same problem, I clarify external display part a little more.

Right after power up and before logging in, iMac does not show pictures on an external display. Only after you login to the iMac, the external display shows your desktop. So, how do you login, if the internal display does not show anything? After power up, press the key of the first letter of your user name, then press the return key. Next, type your password and press the return key. Now you are logged in. If the black screen is caused by the broken internal display, I think the external display will show your desktop. If the problem is in the logic board like mine, the external display stays black.

Regards,

Tatsuya Minami

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