Mid 2011 27" Sometimes Video, Sometimes Nope

[Jimmy-Chivas]

Just looking for some advice here on how to deal with this issue.

Recently picked up a new to me iMac. Price was nice, so I couldn't help myself. Currently got it completely tore down and cleaning it out, re-applying thermal paste and that special GPU paste, etc.

Before the teardown the video wasn't coming on several times in a row. Got the chime, fans spinning, and all that good stuff. After a few tries video came back up, I ran the onboard Diags. No problems found.

It's got the Radeon 6970, which I hear is notorious for issues.

Anyway, I carefully checked the cables and connectors on the logic board during the teardown, all connections seem okay. I'm going to clean up the GPU and re-grease it.

Based on my description, what should I try? Suggestions? I forgot to check and see if the back light is the problem. I suppose the back light could come one intermittently? I should mention that the display is not dim when the video does come on. The video looks good and I see no sign of dimming, in case that helps.

Would taking the extra step of baking the GPU be worth a try given what I've described?

Or, does anyone have a compatible pre-flashed Nvidia GPU they wanna sell me for this unit? Thanks.

 

[MrZupp]

I had a case with an 27" 2011 iMac, the display turned on and off randomly, even though the machine did chime and I had fan spin, turned out the power supply was on it's way out, I replaced it and now I'm writing this on it ( happened around 8 months ago ) Also, I do recommend you to get another GPU since that Radeon wil 100% fail ( if you want to use it just for browsing and stuff, you could upgrade to a kepler gpu with full support in big sur, otherwise get an AMD wx41xx to get full support in Monterey and possibly Ventura, that's just my recommendation )

 

[Jimmy-Chivas]

I had a case with an 27" 2011 iMac, the display turned on and off randomly, even though the machine did chime and I had fan spin, turned out the power supply was on it's way out, I replaced it and now I'm writing this on it ( happened around 8 months ago ) Also, I do recommend you to get another GPU since that Radeon wil 100% fail ( if you want to use it just for browsing and stuff, you could upgrade to a kepler gpu with full support in big sur, otherwise get an AMD wx41xx to get full support in Monterey and possibly Ventura, that's just my recommendation )

Thanks for your input.

This unit seems to either boot with video or boot without video, and nothing in between so far from what I can tell. Video hasn't abruptly quit after booting with video. But also, I've had a relatively short time with this unit.

I think it could very well be a failing PSU like you say. If the GPU were faulty I would expect other symptoms, but who knows sometimes.

Going to button this unit back up today after a complete cleaning/re-grease and see what happens.

 

[MrZupp]

Thanks for your input.

This unit seems to either boot with video or boot without video, and nothing in between so far from what I can tell. Video hasn't abruptly quit after booting with video. But also, I've had a relatively short time with this unit.

I think it could very well be a failing PSU like you say. If the GPU were faulty I would expect other symptoms, but who knows sometimes.

Going to button this unit back up today after a complete cleaning/re-grease and see what happens.

Good luck! And please let me know what caused the issue if you find out.

 

[pugxiwawa]

I had similar issue with 2011 iMac for many years now. It would get stuck at video verification step and sometimes doesn't proceed. I ended up installing Windows bootcamp and surprisingly it always boots fine to Windows. Maybe the driver verification is different. Give bootcamp a try if you want to savage the iMac. Good luck.

 

[Jimmy-Chivas]

UPDATE: I finished my refurb on this unit and it seems to be fine now. Seems like it was just a loose/improperly seated video cable. The unit checks out otherwise. I ran some video diags (which I realize now probably isn't the best idea to stress these old machines) but everything was fine.

I recall the (original) owner saying the video card was replaced under warranty from Apple many years ago.

I'm beginning to understand that most 2011 iMacs that still have working video at this point probably have had the video card replaced already. So they will probably be fine for many more years to come. *Unless of course some of you have had to replace the GPU more than once? I really don't know since I am a late comer to these awesome machines. I would appreciate it if some of the old veterans with 2011's can weigh in on this point.

I did a thorough cleaning, inspected the PCB's, PSU, etc. and did a 're-grease' of the GPU and CPU, and this one doesn't seem to run toasty at idle anymore. Hopefully they run their new OS (Linux/Zorin OS) for many more years!