I would not have thought you would need a high power iron to work on the PSU board. I hope we can patch this up although it won't be pretty when we've finished. I am still hoping to see the box work but if was a cat it would be really short of lives by now. By the way the PSU board is only single sided (tracks on one side only and no internal ones) and does not have plated through holes and so solder will not be drawn into the holes. The cause of your difficult in soldering is due to damaged tracks and missing pads - nothing to solder to - the one leg of R91, for instance is surrounded by fibreglass and not copper.

I've got things to do tomorrow so do not expect quick replies.