Bizarre behavior on my iMac screen

[iRock1]

Hello, I have an iMac late-2009 with Core i5 @ 2.66 GHz, 8 GB of RAM, 1 TB HDD, 512 GB SSD and ATI Radeon 4850.

One day I left my iMac active and alone for a few hours. Then I went back and found out that the system restarted itself (I don't know why) and was stuck in the Apple logo screen with the loading bar frozen halfway, with weird cyan squares and pink vertical bars.

I had to turn off the Mac manually, turned on but then the same thing happened again. Mac stuck in the Apple logo screen and the loading bar frozen halfway.

I repeated this about ten times -- I even tried to boot up from a couple of external drives with Time Machine backups, with no success. Suddenly, at the 11th try the desktop appeared normally.

However, after a while those weird pixels started appearing in certaing areas of the screen again.

Finally I tried to play a video in VLC. Everything was kind of fine until the screen got stuck again, however this time it was the image and the AUDIO too that got stuck.

Nowadays I just can't access the desktop, since the display steel freezes in the boot screen with those weird pixels, pink bars and the loading bar stuck in the middle. However, it seems like the system do reach the login screen, since despite the aforementioned, I can hear the sound of a couple of notifications that can only be heard in the login screen.

Somebody told me it could be a RAM issue, but I played around with the modules, I took off some of them, change others... and then nothing, so it looks like it has nothing to do with this.

Ideas?

 

[coso]

I think it might be the GPU failing

 

[burka_tamas]

Sure

 

[ptfuzi]

If it's not the RAM it's the GPU

 

[InuNacho]

GPU failure.

 

[rpmurray]

It is most likely the GPU on the video card. Most often the symptoms are the black screen of demise, but sometimes you get what you see. There are some videos on Youtube of people baking the video card and then having it work for a while longer (it's a crapshoot on how long). You could also try replacing the thermal compound on the GPU to see if that makes a difference.

Have you ever opened the iMac? If it's never been opened then the fans are likely caked with dust, cat/dog hair (if you have either or both) and whatever other crud it sucked up off your desk. Cleaning them may help.

Where are you using it and what is the ambient temperature? If you're still getting any video then you might try aiming a desk fan at it to see if it'll let you get to the desktop and then download something like Macs Fans Control and have it ramp up the internal fans to keep things cooler.

 

[Nguyen Duc Hieu]

It won't make any difference.
Your GPU has failed.
I got the same machine, same GPU, same symptom.
I took out the GPU, send it to a laptop repair shop to rebake it on professional reflow station. Couldn't fix it that way.
I bought another MXM card and my iMac was working again.

 

[rpmurray]

It won't make any difference.
Your GPU has failed.

Agreed that this is the most likely. But trying a few other no-cost/low-cost things first wouldn't hurt. That is, if the OP is comfortable in opening up the iMac and fiddling around in there.

 

[Fishrrman]

I'd agree with the above speculation on "GPU failure".

BUT...
A 2009 iMac is now going on 12 years old.
Unless you can repair it VERY cheaply (say, under $25), it's not worth fixing.

Time to start shopping for a replacement, either new or Apple-refurbished.

The old saying applies:
"If you NEED now, then BUY now".
Sounds like "you need NOW".

I'd be looking at either the new m1 24" iMac
or
Perhaps one of the 2020 27" Intel iMacs.
(If you're a bootcamp user, you'd probably want to stick with Intel)

BE AWARE that new large-screen m-series iMacs are coming in the future, but it probably won't be until the November/December/January timeframe. I could be wrong.

But again, since your current iMac is no longer functional, you are in a "need now, so buy now" situation...

 

[Nguyen Duc Hieu]

I'd agree with the above speculation on "GPU failure".

BUT...
A 2009 iMac is now going on 12 years old.
Unless you can repair it VERY cheaply (say, under $25), it's not worth fixing.

Time to start shopping for a replacement, either new or Apple-refurbished.

The old saying applies:
"If you NEED now, then BUY now".
Sounds like "you need NOW".

I'd be looking at either the new m1 24" iMac
or
Perhaps one of the 2020 27" Intel iMacs.
(If you're a bootcamp user, you'd probably want to stick with Intel)

BE AWARE that new large-screen m-series iMacs are coming in the future, but it probably won't be until the November/December/January timeframe. I could be wrong.

But again, since your current iMac is no longer functional, you are in a "need now, so buy now" situation...

I wish OP followed your advice and dumped his iMac to my house...
I'd pay for the shipping and carefull packing....

 

[iRock1]

It won't make any difference.
Your GPU has failed.
I got the same machine, same GPU, same symptom.
I took out the GPU, send it to a laptop repair shop to rebake it on professional reflow station. Couldn't fix it that way.
I bought another MXM card and my iMac was working again.

I'm not familiar with the internals. Is it possible to replace the GPU without changing the entire motherboard? Do you have the info of some reliable and cheap store?

I wish OP followed your advice and dumped his iMac to my house...
I'd pay for the shipping and carefull packing....

I'd gladly give it to you! The thing is... I live in Nigeria, so I'll need about $1,000,000 to cover those shipping and packing costs.

 

[iRock1]

It is most likely the GPU on the video card. Most often the symptoms are the black screen of demise, but sometimes you get what you see. There are some videos on Youtube of people baking the video card and then having it work for a while longer (it's a crapshoot on how long). You could also try replacing the thermal compound on the GPU to see if that makes a difference.

Have you ever opened the iMac? If it's never been opened then the fans are likely caked with dust, cat/dog hair (if you have either or both) and whatever other crud it sucked up off your desk. Cleaning them may help.

Where are you using it and what is the ambient temperature? If you're still getting any video then you might try aiming a desk fan at it to see if it'll let you get to the desktop and then download something like Macs Fans Control and have it ramp up the internal fans to keep things cooler.

Oh, now that you ask about opening the iMac before, I came to remember that many years ago I asked a friend to open up that iMac and replace the SuperDrive with a caddy and SSD.

The thing is that during the opening process - I was there - he screwed up a flex cable (don't remember which exactly) and the filaments were loose.

In the end we just fixed the problem using a needle and superglue, lol. After that everything kept working fine for a long time. Then I put the iMac in a storage deposit for around three years, until early-2021. At that point I took it out and it was working perfectly again - except for a couple of bad USB ports and the FireWire 800 one - until it started displaying those screen issues about two months ago.

 

[Nguyen Duc Hieu]

I'm not familiar with the internals. Is it possible to replace the GPU without changing the entire motherboard? Do you have the info of some reliable and cheap store?

Yes, it's possible. the GPU is the small MXM card right next to the DVD drive (now the caddy bay in your iMac).
For the repair shop, you have to search yourself in the neighborhood. I'm from Vietnam and although labour cost is relatively cheap here, they would charge at least US$70 for a replaced GPU.
If only the cable are broken, you can buy them cheaply. I guess it's the slim V-sync cable (on the top left) or the fat LVDS cable.
Search Youtube iMac 2009 for a video on how to open your iMac and what needs to be cared about.