(late 2012 iMac) Black screen 21,5"

[DavidJms]

Hello,

I've tried to change the HDD of this iMac to an SSD and also cleaned it, after i was done (i fully disassembled it and cleaned it with compressed air) I've noticed that i have broken the display ribbon cable which I have later replaced, but the Mac still wouldn't show me any picture, then I connected it to an external display where it posted after like 4 minutes, i got into the EFI installed Windows10 then when it was time for the GPU drivers the picture just died, nothing was on the external display. I thought maybe it hated windows or something so i started installing MacOS, which I haven't finished yet. But it still wasn't displaying to its own screen, even after reconnecting it many times, it only displays to an external display, what could be the problem? I live in Hungary where iMacs aren't really popular so there's no nearby repair shop (I gave it to one, but they didn't even know how to disassemble it) The reason I tried to install Windows and MacOS that maybe they will see the iMacs own display.

As I know it the display is not damaged, and the iMac still functions as normal, although the fan is really loud but I think its cause of no OS

Specs of this machine:
-i5-3330S
-GT640EM

(I also don't really know how Macs work I've always been a Windows and Samsung user, I just got this Mac as a gift from my grandma's friend)

Thank you for any of your suggestions!
Regards: D.

 

[DavidJms]

The GPU might be faulty, after reinstalling windows a couple of times every time I try to install GPU drivers the screen just goes blank.

 

[Nguyen Duc Hieu]

The GPU might be faulty, after reinstalling windows a couple of times every time I try to install GPU drivers the screen just goes blank.

Did you disassembled the GPU heatsink as well? Something went wrong like missing thermal paste on the GPU chip?
Or screws untightened?
If the GPU is still good, the above issues may cause it overheating and shutdown.

So, if you are not afraid of wasting time, maybe you can disassemble and reassemble the iMac one more time, this time carefully check every details.
Somehow doing so help the iMac reconnect every loosen links and work again. Let's hope so.

 

[DavidJms]

Did you disassembled the GPU heatsink as well? Something went wrong like missing thermal paste on the GPU chip?
Or screws untightened?
If the GPU is still good, the above issues may cause it overheating and shutdown.

So, if you are not afraid of wasting time, maybe you can disassemble and reassemble the iMac one more time, this time carefully check every details.
Somehow doing so help the iMac reconnect every loosen links and work again. Let's hope so.

Hello,

I did not disassembled the motherboard it self (or logicboard)
it just shows me no picture on the internal screen only on external screen. I reasembled it many time making sure I connect everything right.

 

[PaulD-UK]

Quote: "...i fully disassembled it and cleaned it with compressed air... I've noticed that i have broken the display ribbon cable which I have later replaced..."

What broke? How? Did you also damage the ribbon cable connector on the logic board?
I've just watched a YT video where a guy ruined an iMac Pro by damaging both sets of logic board connectors whilst dismantling it, without even realising it...
He ended up with exactly the same symptoms as you.

 

[DavidJms]

Quote: "...i fully disassembled it and cleaned it with compressed air... I've noticed that i have broken the display ribbon cable which I have later replaced..."

What broke? How? Did you also damage the ribbon cable connector on the logic board?
I've just watched a YT video where a guy ruined an iMac Pro by damaging both sets of logic board connectors whilst dismantling it, without even realising it...
He ended up with exactly the same symptoms as you.

Only the cable i think, the connector on the logic board doesn't seem to be damaged in anyway. How could I can sure its not damaged, or its just some other issue, but you might be right....

 

[DavidJms]

Now nothing shows on the external screen