Okay, I'll do a power check later to see if the LED turns on as they are supposed to.
Unfortunately I can't (or don't want to) check the boot screen right now. Last time I used my Commodore monitor, it was making a quite noisy high pitch sound, which I understand is a sign of it giving up. I read that if it does give up, it can be hard (or practically impossible?) to repair, so I'm currently looking for someone that can perform a repair of my monitor for me. I've emailed a company here in Sweden, hoping the guy running it can help me although have not gotten a reply yet.
I'll tend to the cap you've mentioned and fix the blob of solder.
For checking the pins on the expansion, what should I have the multimeter set to? My knowledge in electronics is very limited as you might understand by now
If all checks out, there is no more to repair.
I sent my A1200 for repair like two years ago, and it has been re-capped, but it seems that after I received it, it now has issues. Found a guy with the same problem as me in a thread, and they're discussing memory issues:
https://www.radios-tv.co.uk/community/vintage-computers/amiga-a500-graphics-problem/ although I have no idea if this is the case or not but the graphical issues seem to be the same in games. Everything seems to work just fine, besides having these strange corrupted graphics. Due to the monitor issues, I basically just packed away the 1200 again. Figured it wasn't worth it if I risked killing my monitor.