I was recently working on my System 1 totem pinball machine, added some lights and cleaned up a bit under the playfield. and suddenly switch 40, for the #1 & #3 rollover buttons stopped working, the connections on the switches work fine, and I checked with a multimeter and it leads all the way back to the diode board. not sure why its not working.. Don't think it has to do with the CPU because everything was working absolutely perfectly until I went under the playfield and put in some new LEDs... any ideas?

The Return and Strobe is working id assume, as B,C and D are working as well as drop targets 1 & 6... now that you mention it though, the D rollover and A both register when either of them are pressed.

Oh haha makes sense! A and D ARE connected! Update, I'm in a bit of a tough spot.. I'm trying to learn to repair these machines and im a total newbie, it seems while trying to troubleshoot a switch on my system 1 gottlieb totem machine I put a multimeter set to continuity on the wrong end of a switch matrix diode and the other end to switch 40, the whole machine went out and smelled faintly of melted plastic.. I found that one of the 1n270 diodes on the part the multimeter was touching has blown... game turns on, displays show, lights are on and high score pops up but now the game won't start, so I've got two problems, the original switch (switch 40) not registering and now whatever I have done with my amateur and foolish repair attempts, I was wondering if anyone may have an idea of what I might have done to the machine

Holy smokes, I really messed up with that! I tested the fuses, an they are all working fine here's a pic of exactly where I put the Multimeter when testing and one of the diodes appears to be fully dead.

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Good to know, I have a hunch that what might've happened it that the Multimeter sent an electrical charge that the diode was supposed to supress, and I might've sent a high voltage signal upwards to the cpu/driver board in the machine? is it possible that I messed up the CPU? its still playing a lure chime sound every ten minutes, showing highscores and all the lights work.. or do you think its board related?

That sounds like its probably the problem! lesson learned, don't check continuity with the game on!! Ill replace the mpu and switch diodes and give an update then. Thanks so much!