I've picked up a nice almost working Apex 200(?) Turbo XT complete system (system unit, monitor, keyboard, mouse) but it's suffered from a bad battery, like so many other systems of this era.

In addition to that, it has a blown tantalum capacitor and the +12v and -12v rails shorted and burned a 1/8" hole through motherboard at power connector.

As it is currently, it powers on and self-checks but won't boot from floppy. I am not sure if that's due to a bad drive, bad floppy, or something generally wrong.

I've pulled the board out and cleaned it up and traced enough that I think I have a good handle on what needs to be done.

The green boxes are two capacitors need to be replaced. One is shorted tantalum, the other is a smaller tantalum of unknown value but possibly the same as C225.

The teal circles are vias that are no longer connected, so I'll need to repair those somehow. They're blocked by solder or debris that I'm not really able to clear so I might just run a jumper wire around to the back.

The yellow line is a broken trace at some point or another, not sure exactly where since it looks good.

The real question mark for me are the +-12v lines. Everything seems to be working fine-ish other than the floppy booting, and as far as I can tell nothing on the motherboard even uses 12v; is it simply provided for ISA cards to use? The orange and purple lines are my best guess for how the 12v lines were connected based on tracing back from ISA connectors...

As a final problem, I'm having a real hard time getting solder to adhere to the copper traces, even using plenty of flux. It's just beading up and not sticking, any advice on what I'm doing wrong there? I used 5% vinegar to dissolve corrosion and cleaned with ethanol and rinsed with tap water, so perhaps I've done something wrong there, but fixing those traces and vias will be difficult if I can't get solder to stick to the traces...