No video output on mid-2011 27" iMac

[Aidoru2K]

Hi everyone, after a regular reboot I seem to have lost video output on my 27" EMC 2429 iMac with a 6970M.
It boots up regularly but the screen stays black, I already tried resetting the PRAM and connecting an external display but it didn't work.

Luckily I can connect to it via VNC and I noticed that there is no mention of either the display or the graphics card on System Information. The Graphics/Display section is just empty, and the resolution is fixed at 1280x1024.

I don't think the video card has ever been replaced, and to be honest I only experienced a few vertical lines from time to time. Did it die suddenly? Can the iMac even boot up with a non-working card? Since I already cleaned my backlight diffuser and installed an SSD a few years ago, should I risk removing the 6970M and baking it?
Thanks!

 

[krazzix]

There is no risk in removing it since it already broke. I would recommend baking it. It worked for me and several others here.

 

[herrdude]

You could bake your card but will find yourself doing it again down the road.

For all the effort that it will take you to bake it, I highly recommend this thread: https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/

It is a long-term solution.

 

[fairbanx]

My problem is similar. I have an iMac 27 mid 2011 i7 3.4 GHz AMD 6970M on my desk which delivers no video output, also it doesn't work via an external monitor. I opened the machine, replaced the battery and checked the LEDs on the logic board. Only LED 1+2 lighting up. I baked the GPU once for 8min @200° Celcius with no success, and a 2nd time for 8min @210° Celsius with no luck. Only LED 1+2 are working again (I have to admit that I only put the pieces together roughly without thermal paste to check whether LED 3 will light up or not. I turned on the machine only for some seconds). Any further ideas or should I go for a new GPU?

 

[krazzix]

I have to admit that I only put the pieces together roughly without thermal paste to check whether LED 3 will light up or not.

Actually in my case I also had only 2 leds lighting up. I decided to put everything back together anyway and boot it to see what happens, and what do you know, it worked again.

 

[fairbanx]

Actually in my case I also had only 2 leds lighting up. I decided to put everything back together anyway and boot it to see what happens, and what do you know, it worked again.

Ok, thanks for sharing your experience. Then I will do the same and try before ordering another GPU. But this will take a while as I currently have no thermal paste at hand.