Williams System 9 CPU/MPU board.

So...
I thought the hole in the board by IJ17 and the wires strung though it might be a problem down the line, so I found a replacement board.

Checked all the chip connections, plugged it in, checked all my connections, and I get Error 7, which is a system failure.

Phooey.

And I saw...
When I was poking around checking connections and things, a puff of smoke from the area of the crystal. And the burning smell I am becoming too familiar with lol. I couldn't figure out where it came from exactly though.

So far...
I swapped the game ROMs out with the holey board, reseated U18, checked that the rest were seated well (without removing and reseating) swapped the crystal for the crystal in the holey board, and still get the same issue.

I am getting 5 volts at 5V on pins 4,5, and 6 on 1J17. On the power supply, pins 7,8,9 and 10 on 3J6 have 5V.

Maybe Related??
F2 fuse kept blowing...I finally READ the fuse and it was a 5 volt, and not a 2.5 volt sb. Fixed that. Blew it again. Hmm. Schematic shows the one directly above that is a 'do no use' fuse. But there's one there. I removed that, and changed F2 again; seems okay now...but could a wrong fuse configuration (for lack of a better way to say it) make something on the board go out?

Yes, I know I can send it out for repair, but then I won't know what it was or how to fix it myself. lol though if I did know how to fix it myself, I probably wouldn't have any problems sending it out. If anyone can help me fix this, I know the people here can.

Yeah, that's what I put in after I looked at the schematic.

UPDATE:

I thought the problem was with the CPU/MPU unit. Now, I don't, but I don't know where else it could be. I got the old board (with holes and interesting fixes) working again and put it back in the game, and it's doing the same thing the newer board was.

First turn on; loud loud hum. At this point, I turned it off, but with the other board, I didn't, and eventually there was a burning smell, a small puff of smoke in the backbox and F2 blew. I thought at the time, it was because F2 had a wrong fuse in it, and the one above it was also being used even though the schematic says not to. But fixing that didn't make it work right.

I rechecked the solder points on the transformers, the fuse next to them under that metal grid thing, I've getting 5 volts to the CPU board, the game ROMS are good, the crystal is good. The connectors are well seated as are all chips. I don't think the system fail code is because of a failure on that board. But I'm not sure how to check what IS causing it. Or what to check.