Amp repair; Tooooo muchhhh feedback
So I've a little 60W combo amp for about 5 years now and a few years back I had to get the input jack replace. I send it to this local electronics shop to get fixed and everything was good until about six months later when it developed a reaaaallly loud static that muffled out the actually sound of the instrument it was amplifying. So I just put it away and used my other amps.
I pulled it out today when a buddy came over to jam and we got it to work, but it's still really muffled and static-y, and very once in a while it would throwback the gnarliest feed back I've ever heard. Like enough to scare the neighbors.
I've decided to take it apart and fix it myself (as I now have a pretty decent understanding of electronics). I took it apart and there's a scrape on the circuit board, but the copper is still in tact; it just scraped the green insulation or whatever. The soldering job on the input jack isn't the best Ive ever seen either.
So basically I just need advice on what you all think it is and how I can fix it. Thanks!