Small Square Pixels Display Problem

Hello,

I've encountered a problem with my iMac as of yesterday and I was wondering if anyone else had a similar issue. My mac freezes up and I get small square pixels all across the screen. I have to pull the plug in order to shut it down and restart it. Even in safe mode after a while I'll get vertical pixelated lines down the screen. I'm assuming it's a display issue but I'm not sure. Below are the specs for my iMac along with 2 pics. Thanks.

iMac : 21.5-inch, Mid 2010

Processor : 3.06 GHz Intel Core i3

Memory : 4 GB 1333 MHz DDR3

Graphics : ATI Radeon HD 4670 256 MB

Software : OS X 10.9.5 (13F1066)

It appears the graphics adapter in your iMac is defective. To test it, attach an external monitor or TV and see if it displays the same as on your iMac. If it does, the graphics adapter will have to be replaced. Replacing the graphics adapter in your iMac is not an easy do it yourself job and a new adapter is expensive. If you wish, take your iMac to an Apple store and let them run diagnostics (diagnostics are free) and get an estimate of repair cost.

RjX14 said:

Hello,

I've encountered a problem with my iMac as of yesterday and I was wondering if anyone else had a similar issue. My mac freezes up and I get small square pixels all across the screen. I have to pull the plug in order to shut it down and restart it. Even in safe mode after a while I'll get vertical pixelated lines down the screen. I'm assuming it's a display issue but I'm not sure. Below are the specs for my iMac along with 2 pics. Thanks.

iMac : 21.5-inch, Mid 2010

Processor : 3.06 GHz Intel Core i3

Memory : 4 GB 1333 MHz DDR3

Graphics : ATI Radeon HD 4670 256 MB

Software : OS X 10.9.5 (13F1066)

Click to expand...

I have had the same problem for some time with a 27" iMac of slightly newer vintage. Your screen shot looks very much like mine. That pixellation appears at random - sometimes with intervals of several weeks with no problems in between. I haven't been able to find a pattern or cause. Everything (including the graphics card) tests out on the hardware check, but I finally took it in to an Apple Store Genius Bar. They ran several tests - including one that went overnight - and still found no failure in the hardware components. Their only conclusion was some sort of a software problem. They wiped the hard drive, and I reinstalled from my Time Machine. Everything worked fine for about 5-6 weeks - - then I started getting the same thing happening again. It has become more frequent of late - including this morning, which is why I was searching again and found your post. The only thing I've ever been able to attribute it to was switching desktops via Mission Control. Even with all programs and windows on a single desktop, it has still happened. The graphics card has never failed a test, though, and I didn't want to pay to replace it unless I was sure it was going to solve the problem. The other idiosyncratic item is that sometimes the pixellation will disappear after a restart, but sometimes it just remains - then goes away on its own. The only thing I've noticed consistently is that the little squares seem to blink when the internal drive is being accessed. That one really has me stumped.

From recent experience, I learnt that Apple Store does only limited diagnostics when problems such as this appear and doesn't go into the machine's own system log to find what happened at the point of the errors. I watched an engineer do this in front of me and asked why this hadn't been done (it took two minutes) before major repairs, which didn't solve my problem, were carried out. Ask them to do this.

You can look at the records yourself and see a second by second account of what your Mac is doing. Understanding is another issue!

Find your system log: Applications > Utilities > Console

Looks like this: