Red and green square dots?

Apple didn't make these cards, and nobody makes them anymore.

Oh, I know they did not make the cards, but ultimately they are responsible for the cards that are in the machines they sell. Whether it is an ATI or an Apple recall, I think this thread has proved a significant and consistent manufacturing defect in these cards.

We had 2 of these machines in our office and one even had the card replaced via AppleCare, but both exhibited the same problem. The same issue came back on the new card after a few months. AppleCare is now long expired.

So I spent a couple of hours yesterday with a lot of nervous sweat, taking my $3000 iMac apart and cooking the video card. 24 hours later I can say there are not any graphic artifacts or freezing. Time will tell. I'll keep the forum posted on my results.

I am reminded of a quote from The Graduate 😁...

Mr. Braddock: Ben, this whole idea sounds pretty half-baked.

Benjamin: Oh, it's not. It's completely baked.

=============================================

You might say that the ATI graphics cards were half-baked.

Just so everyone knows, I updated to Yosemite thinking it would help and it made the problem worse. =(

Thought I'd join this thread and share my story. I have a late 2009 27" iMac i5 with 8gb of ram and an ATI Radeon HD 4850 graphics card.

On Thursday (last week) I started to experience random glitches on the display and the machine froze. I Turned it off and back on only to see the vertical lines and it would not boot past the apple logo. It would however boot into safe mode. Reseting PRAM and SMC worked briefly before the lines returned and the machine froze. I updated to Yosemite which seemed to fix the issue but I ran a web based GPU stress test which brought back the symptoms.

After scouring the internet and reading this thread I had a strong feeling the issue was with the GPU. I'd read about the bake trick and decided to give it a shot. My macs been running perfectly since Saturday without a glitch, and I'm a heavy user (its been running all day every day since but switched off in the evening). So far so good but I'll keep you updated.

If anyone would like to have ago at baking, the ifixit instructions mentioned earlier in the thread are excellent. I used steps 1 to 9 but did not unplug the Graphics card temperature cable as it looked very difficult to reconnect. The thermal paste on the GPU and chips had dried out and cracked in places as can be seen on my heatsink.

.

Here's my card baking...

plkay - what's your "ahimmering green-n-purple pixel" status these days?

Much to my chagrin.. "they're back"!!

Despite MONTHS of not a single instance (with prefs set to NO sleep mode - hard drive or monitor) under all iterations of Mavericks, once I upgraded to Yosemite, they've returned... at first, dancing and shimmering on the periphery to the top left and right hand corners of my 2010 27" i5 iMac.

After "inactivity", there seems to be only one or two lines of these to the upper left, which only seem to "dance" when typing or moving my mouse... and a 2" square grid of them in the upper right hand corner, that "blinks" randomly, regardless of other activity...

sigh....

Does anyone believe that Apple will EVER addres this issue? Even Scion eventually did a "courtesy" recall/replacement of the rear hatch handle on 2004-2006 xB's, when thousands experienced failures from a simple hardware design insufficiency...

They can build a multi-million dollar, alien ship eco-campus and substantially improve employee benefits, but they're unwilling to assist loyal acolytes?

As an aficionado since 1984, I can only say "shame on Apple"!

Same here:

After MONTHS of "ficker-free" performance, the minute I upgraded to Yosemite, they've returned with a vengeance...
Not at all confident in my skills to remove-bake-reinstall the video card: Does anyone have suggestions for a replacement card (of a different manufacturer)?

Too weird: Installed Macs Fan Control App, and turned off a small external fan I'd been running for years (blowing across the top of my 2010 iMac 27" i5)...

Everything froze: Had to manually restart - and restart a second time.

Eventually everything came back - with the "graphic problem" alert (see below) that I'd never seen before (perhaps telling us this IS a "graphics problem", or that Apple might actually be collecting data on the issue?)!

My display has never had greater depth and richness of color, nor such crystal-clear focus: No shimmering appeared for the longest time, and when it did it was extremely short-lived (nothing happening at present).

Just as I'm hesitant to perform the "baked board" initiative, I'm equally uncertain about adjusting the fan speed/temps with this app: Does anyone know of a "how-to" blog that's reliable and safe?

One thing: Everything seems to be running a bit slower, and while typing my cursor seems to randomly jump to lines other than the one I'm typing in....

Your thoughts, please?

I After my 'bake' I installed a trial of istat Menus 5 to monitor the temp of my GPU and ran my fans at a medium setting for a while before switching to the default setting. This did not create any issues and obviously reduced the GPU temp. Although mines a late 2009 machine, just for reference here's a screen shot of my temps. I currently have mail, iTunes, safari, garage sale and iPhoto running.

Thanks for the info!

Was I mistaken, or did earlier posters mention better "non-shimmering" performance by actually RAISING temps?

BTW - ever since the "double restart" and that graphic problem alert, I've not had any shimmering .. and my display is more brilliant, richer in color, and sharper than I've ever seen it: go figure!?

You really need to bake your graphics board for a permanent fix.

Adjusting the fan speeds might get you by for awhile but eventually it will get so bad that it will not help at all.

That was my experience anyway.

Rich

I agree with Rich. I had read about fractures in the solder developing and perhaps increasing the temperature is expanding the components and improving connections, hence the need to reflow the solder on the card. I was completely sceptical but if it worked for us and for others I'd give it a go.

Justin.

PhilP2 - that's the same system readout as the one from my OEM ATI Radeon HD 5750 thaet came with my mid-2010, i5 27" iMac...

I'd run for over a year without pixelations... until upgrading to Yosemite a couple of days ago.
Checked to see if my "energy saver" settings had been restored to their defauilts (NO).
Problem seemed to increase with mouse movement or typing...

System then froze: Had to hard restart - twice (interrupted the first restart with a second, when it stalled).

Now, no problems reoccurred and strangest of all - my display has the richest colors I've (never) seen since it was purchased - more vivid, sharper, deeper!

I might also add that prior to this reoccurrence, I'd been running a small fan across the display top to more quicky dissipate the heat that it was emitting - and after reading several posts suggesting higher temps seemed to alleviate the issue for some. I thought perhaps returning to "factory cooling specs and conditions" might aid.

So far, it seems to be working... and I'm thoroughly enjoying my "new" monitor!
Does anyone have an inkling as to why it seems so MUCH better (other than to postulate that - as a light bulb about to burn out - it may be brighter and better prior to imminent failure)?

I had my video card replaced twice and my logic board on this 27" mid 2010 iMac and it got rid of the problem for a good year. Ever since I installed Yosemite...it came back and even worse it locks up my computer. When I did a hard reset it reported a "Graphics Error" to Apple but didn't give me a crash report.

This is depressing. 😟

Here are some new members to our club: Imac display issues following Yosemite upgrade

Ok so I got thinking is this environmental? Last winter when temperatures reached freezing was when my iMac started to experience these problems and my computer is in a cold room next to a drafty window. I had the video card and logic board replaced and it's been fine until now when the weather started to get cold again. Could the heat of the iMac combined with the cold temp cause the thermal paste on the GPU to crack and flake off?

It's kind of similar to the ATI cards in Xbox 360 where people wrapped a towel around them to try and reflow the chip. Is it just that? I'm going to try to raise the temp in this room to see if that makes any difference to the frequency of my pixelation problems before I consider baking the video card.