Fixing a Borken(sic) iMac Display

My 2009 iMac decided to break down in the most unfortunate way just before Christmas.

I normally leave it on all the time, and when I came back to it, the screen looked strange with small yellow blotches all over the screen and was unresponsive.  Since nothing else worked I did the "hold the power down button for 10 seconds" thing to force turn off the machine and waited about a minute before restarting.

Bad news, the progress bar crept to about 70%, then the screen got corrupted again and the boot sequence failed.  This was annoying on more than one way in that I had recently upgraded the 1TB hard disk to a 1TB SSD for massively increased performance. (I would 100% tell anyone who wants to get more performance out of a machine to a) upgrade the RAM and b) upgrade to a non spinning-rust storage instance.  I digress).  So, this is what I was seeing:

I reset the PRAM and booted into safe mode.  This took a very long time, but I did manage to get a login screen and the desktop, but with VERY slow video performance,  and still had 5 yellow/blue stripes down the screen.  After logging in, I could reboot it back into normal mode, but it stuck at the Apple logo screen and failed to continue.

This is what it looked like in safe mode:

Redrawing the screen was painful, as you could almost see it working out what to do.  Video playback didn't work, but I was able to fire up Citrix and work from home for a while, but really, really slowly

.

I did some searching on the web and it looked like it was a video card issue.  Since it was well out of warranty, I phoned my local may authorised repair place and they agreed to take it and have a look.  Unfortunately they confirmed that it looked like a video card issue and there was very little to be done since these cards cannot be sources easily any more and are not manufactured.

So, I bit the bullet and ordered a new 2017 i5  iMac with 1TB SSD and waited for the pain to subside from the payment.

In the mean time, I did look further and found a reference to an iFixit post (see here ) which suggested dismantling the iMac and roasting the GPU in an oven for 10 minutes to rement and dry solder joints.

My hardware experience is very limited.  I added a 1 Mhz to 2 Mhz switch (yes, mega, not giga...) on my first Acorn Atom to boost the 6502 processor, but that really was the level of my hardware experience.

But nothing ventured..., so I bought all of the bits and bobs needed from Maplins (R.I.P.) and 3 weeks ago, after watching both of his video tutorials, decided to bite the bullet and give it a go.

Well, it wasn't easy, but the worst part was putting everything back together.  The ribbon cables on that machine are a real bugger to put back correctly.  I took both videos and went with a combination of removing as little as possible to get to the GPU and then followed the rest of the instructions, eventually baking the GPU card on 4 little foil pyramids.

Put it all back together and it worked.  Booted to High Sierra and all the graphics stuff works perfectly now.

What did I learn from this?

1. Broken GPU cards can be fixed by baking them in the oven.  It may fail later, but when you're at this stage, anything is worth a try.
2. Go slow and steady when trying some new hardware stuff.  I disassembled and re-assembled over 3 days giving me plenty of time to make sure I didn't rush anything.
3. Rare earth magnets are great at pulling screws from your hand, just as you try to screw the LCD panels back into a chassis... :-)