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The trigger adding another player could be a wiring issue or a switch matrix problem. What does your switch test mode show you? Do you get the same results using jumpers on the of connectors with the pf disconnected?

Good general info on Data East games: http://www.pinwiki.com/wiki/index.php?title=Data_East/Sega

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).

That games magnet board was a junk design. Theres a company that offers a new board just buy that and be done (and reliable).
The ripper was also non functional when I got mine. The fuse was blown. It would work once and the fuse would blow. Bad transistor IIRC. However to be sure temporarily short the lugs on the coil. Does it fire? If it doesnt you need to replace the coil and likely the associated TIP transistor as well.

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.

Sounds like a matrix problem, at least with the trigger issue (switches are on same column). See page 28 of the manual and follow instructions on pinwiki for matrix problems (testing diodes, etc.). Want to start there vs. board. Also verify the connectors are where they should be.

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

Missing coin mech no problem.
Because it's easy to check, I would look at the wiring and make sure the shooter lane switch has one green/red and one white/grey wire and the Launch Trigger has one white/grey and one green/brown.

Pinwiki can get you started troubleshooting the switch matrix: http://www.pinwiki.com/wiki/index.php?title=General#The_Switch_Matrix

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.

I love to see these threads solved. Awesome! Congrats.