Yea so DOA.
I rebuilt the rectifier board and ditched the MPU board for an Alltek.

Following Clays guide, I connect J2 of rectifier and J2 of SDB, coils blow!

The original MPU board and SDB have signs of repair...shit work too I might add, with burn or blown marks on the board and around the connectors. Something bad has happened with the machine at some point but previous owner denies any knowledge.

I WILL double check the coils and diodes this weekend, and if all che k out, I'll try the rotten dog SDB I have handy to see if the issue is with the original SDB.

I wouldn't rush out and buy a new sdb, these things are always fixable, really simple too, and parts are always available.
Personally a board would have to be almost snapped in half before I would give up on it, I am just too stubborn
The Bally / Stern systems are a good start for a beginner because they are so easy to fault find.