Chosen Solution
Sorry for the long post, but I’m trying to be thorough. I may have done the bad thing. I came in to get set up for an event yesterday, only to find that my iMac would not power on. No chime, no whirring of a disk—nothing. It has done this before, and the only thing that helped was to leave it unplugged for a week, then try to boot up a week later. Side note: I was out-of-state over the weekend and don’t know if there were power outages/surges from weather, but we’ll consider it likely. Well, I decided to open ‘er up today as I had seen that there are diagnostic LEDs that can point to the issue. I got the screen off and delicately set it aside only to then discover that I was looking at the troubleshooting guide for the wrong generation and my LEDs are visible through vent-holes without removing everything. I decided just for kicks that I would unplug the power supply from its cables and plug it back in. Got everything screwed back together, screen put on, and it started up! Now, though, the display is a bit messed up and I’m not sure what went wrong… everything displays and I can use it just fine, but green dots and stripes show up in varying places. The pixels aren’t dead; when I hover the cursor over any of those spots, they disappear and show up as soon as I move it away. My question is twofold: 1) should I bite the bullet and buy a new power supply even though it booted up this time? And 2) how do I fix the green-pixels issue? Any help would be appreciated!
Test out that power strip first. I’ve had them go bad totally and just one outlet. As for the artifacts, hook up an external monitor and see if the problem persists. If they show up on the external, your GPU has been hit. Now if facing replacing parts, total up the costs for the parts, then check on eBay to see what your machine is now worth. If indeed you have been hit with an electrical surge, such as caused by lightning, it will have weakened other parts and you may start getting cascading failures, i.e. you replace one part and then the next part fails. I don’t understand the photo you have posted.
I do not like to take chances with power supplies. I think it would be in your best interest to purchase one just in case. It definitely sounds like a power surge hit your computer, and I would hate for it to be damaged by a bad power supply. As for the green pixels, it sounds like those are GPU artifacts. It’s likely that the power surge shocked your GPU. I would replace that as well. You’re fine to use it right now, but you’ll probably notice lots of other issues as you do, so replacing that should be a priority. This looks like the correct part, but double check to make sure. This guide should get you to where you need to be in the iMac. Good luck!
