I would look to see if a diode has come loose, is shorting to a coil bracket, etc first. There could have been a short of the solenoid voltage to the switch matrix for instance already going on in the game and when you put the new boards in, poof good bye switch matrix PIA.

What did it do when it started acting up?

That is where I would start... maybe the switch when activated hit the power feed for the GI or controlled lamps? Something fed some voltage into the matrix and the game wasn't happy. There are a couple other IC's (7406 / 4049) in the path before the PIA so maybe it just affected them.

To test the switch matrix in the game, first remove both Switch Matrix connectors on the top right of the driver board. J2 is Column (green wires) and J3 is Row (white wires).

Then run a switch test from diagnostics, you should get no switches being sensed.

Use an alligator test lead as follows:
Connect one end of the test lead's alligator clip to the column pin, starting at column 1. That's the bottom pin of J2.

Then use the other end of the test lead to touch the appropriate row pins.
Start at the bottom pin of J3, which is row 1. You should see switch #1 indicated (R1C1).

Move the probe to the next pin up on J3, which is row #2. You should see switch #2 indicated (R2C1).

When you got to the top of the row pins, move the clip end to COL #2 (up one pin) and start again with row #1.

Activate each switch in turn by connecting the appropriate 2 male pins on the CPU board with your test lead.

Using your switch matrix chart from the manual as a guide, you may find the faults as your game "sees" on the same switches.

If you get an error in sequence, more than one switch registers at a time or you are missing a row or column - then you know the problem must be on the board. You can either try to fix it or send the board out for repair.

If the above test works correctly, meaning all switches register correctly then your problem must be the wiring or on the playfield.

oh well shit, if all of those IC's are socketed yes you could shotgun it and get it going in minutes. the tough part is finding why it happened in the first place and fixing it so it doesn't happen again.

You can test the 7406 and the PIA with your DMM by the way. I can send you that procedure if need be.

It's probably the 7406. Did you find what caused it?