Stubborn heatsink thermal gunk removal tip
As mentioned above, the heatsink on the GPU was stuck solid. I'd advise against prying it off as the chip underneath is fixed using BGA rather than pins. Heat has been doing its best to break that chip for 20 years so don't help it out by cracking it off with a screwdriver
The safest way to remove it is with a little heat. You can use a hairdryer but I've got a (albeit cheap) rework station with a hot air gun so I set it to 150 and warmed the heatsink up for a few minutes, moving in a circular motion. After about 3 minutes the heatsink released with a very gentle twisting motion.
Unfortunately, the residue left on both the chip and the heatsink was not like any thermal compound I've seen. Maybe it was the 20 years its been on there, or maybe it's just a very heavy duty thermal adhesive but it's thick, hard, sticky in places and won't budge with any amount of isopropyl.
Attacking the chip with a scraper or knife didn't seem like a good idea but I remembered I had a bottle of jollup that I use for removing sticky residue called
Sticky Stuff Remover so I thought I'd very carefully give that a go.
Using a soaked q-tip and being careful not to get the stuff anywhere other than on the chip itself (I've no idea what's in it...), it came off easily after leaving it on for a few minutes to break the compound down. After dying with a lint free cloth and cleaning it again with isopropyl, no old thermal compound remains: -
It's been rebuilt with new thermal compound and fans and I'm happy to say it's all back up and running.
Obviously, feel free to educate me as to why putting Sticky Stuff Remover near a board is a bad idea, but it seemed like the least invasive solution
Many thanks again to Vamino for the replacement motherboard
