Sounds very likely to me too.

Far as some of the coils not firing, continuity test all the fuses with a meter that are on the power supply (top left board) and the PPB (lower left board).

I am using the original DE LAH magnet board with zero issues. Yes, at some point a person can have one of the transistors lock on and blow a fuse or heat the solder up so much that the transistor just falls off the magnet board into the cabinet. That is why I replace all 3 when I work on games that have this magnet board and making sure having the last game ROM installed. No issues after such repair.

I had a very similar switch matrix issue with my LAH. I just don't recall the switches that were registering when they shouldn't had. I do remember my smart missle button was not even registering. I found a broken diode on this remote diode strip shown in the picture just below the right flipper button.

Since you don't have the exact switches acting up, you may have one of the other ones broken. If not any of the three, then it may be on another remote diode strip mounted on the underside of the playfield.

Make sure you tug on the diodes as it may look they they are connected, but may be broken like mine was.

20190706_224322 (resized).jpg

Make sure that you have CN1, CN2 and CN3 plugged in at the top right of the MPU board. The signals for the magnet come from those 3 connectors as to when they should activate.

LAH magnet (resized).png

What was your solution for the switch matrix issue?

Time to test the transistors for shorts that drive the ripper. There will be a Tip36c on the PPB for power to the coil and a TIP122 on the MPU that would make it fire.

Since you have the 2 boards out, best to test all the transistors.