iMac Mid 2011 27" with repeated black screen after repeated fixing attempts - anyone have any other ideas?

[amoxitine]

Hi there,

I have an iMac mid 2011 27" that started black screening last week and since then I have done all of the following, yet I can only get the iMac to boot with the screen working for maybe a few minutes at best before it black screens on me yet again :-

1) I have removed and oven baked the original graphics card twice (200 deg C for 10 minutes) - both times the card started working from 1st boot but then either dies within minutes or black screens again after a reboot

2) I have done numerous PRAM resets and other types of known iMac resets involving the power button / removing the power cable etc

3) I have replaced the firmware battery

4) I bought another 2nd hand graphics card (same model) that was tested as working in another iMac, but put that in my iMac, worked for a few minutes and then died again.

5) Sometimes if I leave the iMac overnight, then strip it down (to where I remove the mobo and reseat the graphics card and then refit everything) again it will start up but then then black screen after a few minutes.


Each time I've used what I believe is decent thermal paste when I've attached the original or replacement graphics card to the heatsink so I doubt that the card is overheating, so I was wondering if anyone might have any suggestions as to what the problem might be? Logic board or another component?

Cheers,

Dave

 

[Cory Cooper]

Hello and welcome.

1) Not sure where you saw "oven baked the original graphics card twice (200 deg C for 10 minutes)" as a troubleshooting step?
2) Good you did the SMC and NVRAM resets. If they didn't help, then it is a hardware issue.
3) Fresh PRAM battery is always a good troubleshooting step.
4) If multiple cards have the same issue, I would lean towards the LCD panel/cabling or the logic board.

It does sounds like either a thermal issue, or another component failing. It could prove difficult to narrow it down, without having other parts on-hand to swap in/out.

If you have an external display available to connect, and the issue doesn't happen on it, then it may be the LCD panel/cabling. If it does also happen on the external, then it's the logic board/video card.

C

 

[amoxitine]

Hi Cory,

Many thanks for your reply, greatly appreciated. In regards to the oven baking of the graphics card, during my iMac black screen research I came across a few videos that demonstrated a fix using this method with the 21' and 27" iMac from the same period, so that's why I gave it a go (plus I did manage to revive an old PC card doing the same thing many years ago so have had positive results previously), but the issue doesn't appear to be caused by the card and is more likely to be as you suggest, either the LCD panel itself or the logic board.

I just need to get my hands on a display port adapter to hook up an external monitor, so I will report back my findings when I've been able to do this.

Cheers,

Dave