I finally fixed the rear panel of my Classic Bally Cabinet. It was actually quite simple and did not require any special bits.
It may look like an heresy to the purist, but compared to the MDF crappy board that Bally provided, it will be a lot better and sturdier.
The most difficult is to actually remove the old soaked panel: I used a rubber mallet and broke it out, so to speak. The board was so bad, it only took a blow to break it:
This is what you get after sanding and priming. The corners holding the legs, will be removed and glued back in place for stronger bonds.
Basically, you are left with a square opening of 1/2 inch thick and a 45 degrees angled opening on both horizontal sides.
The idea is to glue in place a piece of 1/2 inch plywood squarely cut of about 19 x 22 inches (measure to make sure it matches your cabinet). The piece is glued and clamped for at least 24 hours. I use Titebond 3 as a glue. That piece of plywood has a little gouge of 1/4 inch, to hold in place the bottom of the cabinet:
My cut was a little bit too large and I should have done it smaller (in width).
Test fit the board and then glue in place using a few wide clamps.
Once the glue is dry, flip the cabinet over and re-install the corners, while adding some more glue for good measure.
The, re-create the hols for the leg bolt. I used a round file to finish smoothly the openings, and verified with a bolt that it slides easily:
Them a piece of 1/4 inch plywood (approximately 19 x 22) is carefully cut with its two horizontal sides cut at 45 degrees. Make sure that the board fits perfectly:
After gluing overnight, the board is ready for sanding, priming and painting.
It may not be perfect for some of you, but when I compare with the original condition, I like my simple and easy modification a lot:
Once painted, I will add four large gliders (not the stupid and useless tiny Bally gliders) that will hopefully protect the bottom of the cabinet from water damage and humidity, when stored erected.