YLOD... Only After Cleaning

Hello,

I picked up a Used 40GB PS3 Phat, and it was in perfect working order when I brought it home. Formatted a new HDD, logged in with my PSN. But the inside was caked with dust on the inside. Like that was it's side hobby.

So I disassembled, replaced the thermal paste (TM30, after cleaning with 99.9% Iso), cleaned the fan and heat sink and reassembled with nothing out of place.

And now I get the YLOD. Did I do something, because reading up on the issue it seems it can only be caused by blown capacitors but I obviously turned off the PSU before removing and replacing the plug in the beginning/end.

I did the exact same work on my PS4 Pro a month ago and it works perfectly.