Recently I purchased a U/S DMD controller board from a 90's Williams/Bally machine. The board had a hole burnt in it that had been cut out with a dremel tool and very poor repair attempted by soldering a piece or vera board to the main board.
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To repair this board I first removed all the burnt components and sanded the crap and corruption of the board to allow a clean surface. Next I straighted out the edges of the hole use a dremel and file. Next I cut a piece of blank PCB and trimmed it the fix the hole in the main board. Next I taped the new piece of board in place one side and araldite it in from the other. After this araldite had set I did the same to the other side of the board and heated the repaired area with a pre-heater for a couple of hours at about 120 Degrees to really bake in the glue. Next I sanded back excess glue the marked the placed to drill the new holes. After drilling the new holes its just a matter of installing new plated through holes and track.
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The new area is lighter in colour.
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I also had to replace all of the remaining track and holes as they were buggered from heat exposure in the past.
I hope this information is helpful to someone.
So please dont through away your old broken PCB's as most of them can be fixed given enough time and effort. :)