I have an issue with my Comet machine that cropped up last night. I recently acquired this game and have had it working great now for several weeks, no issues. Yesterday, the right flipper started losing power and I noticed the EOS switch was hanging by a thread. I had a flipper rebuild kit on hand so I rebuilt the right flipper and kept the existing lane change switch in the assembly. After I was finished, the flipper worked wonderfully but all sorts of odd issues started happening with the switches. After some testing, it appears to be column 4 which the lane change switch is on. Every switch on column 4 is triggering something incorrectly, with the exception of the 'Left Drain Special' switch that seems to be working okay (although I can't say 100%). I figured it was a diode issue on that column and triple-checked every switch in that column for anything unusual, then every switch on the playfield, and didn't see any broken wires, diodes, shorts, nothing. It's really odd that it literally worked fine right before I did the flipper rebuild and now these issues have cropped up. Any suggestions on what to check? Here are some of the items I've noticed in particular:

-Cycle Jump- Lower and Center Rings cause a tilt, Upper Ring triggers a credit
-Comet Ramp upper switch does nothing at all
-Dummy Dunk Tank Drop Target triggers the outhole
-Lane Change switch scores a bunch of points (unsure of what it's triggering)
-Right Drain Special does nothing at all
-Left Drain Special SEEMS to work but hard to tell if it may be triggering something else too

All other switches seem to be okay: Pops, slings, standups, top lane rollovers, corkscrew switch, tilts, service switches, etc.

I tried clipping the leads on the lane change switch to remove it from the circuit and get the same result on all the other switches.

I'm so stumped because I didn't touch anything else...

Comet sw matrix (resized).jpg

So, in switch test, this is what I see:

With 1J8/1J10 unplugged- no switches are activated
With 1J8/1J10 plugged in- no switches are activated

Then, I tested pressing each switch individually and all of the problem switches in column 4 are activating every switch on their corresponding row.

For example-
Cycle Jump Upper activates every switch on Row 1
Cycle Jump Center activates every switch on Row 2
Cycle Jump Eject activates every switch on Row 3
Comet Ramp Upper activates every switch on Row 4
etc...

All 8 switches in column 4 activate all of their corresponding ROW switches.
What the heck does that mean?

Thanks in advance for any assistance.

So, I jumpered pin 4 of 1J8 to each pin of 1J10 and got the same exact results, every switch (pin) was activating the entire row of switches! Ugh. Any idea what might be bad on the board to cause this?

That was it! Q10 was fried. I happened to have spares by some miracle and replaced it. I only tried the game briefly after the replacement but it seems to be working normally! Now I'll work on putting the lane change and flipper assembly back together and see how everything is playing.

frunch Thank you so much for the screenshots and explanation, it totally makes sense after thinking it through but I just couldn't wrap my head around it before. Thank you!

Thanks for the suggestion @rikoshay, I did check pretty carefully for diodes or switch problems and also took the lane change switch out of the circuit to eliminate that from the equation. Turned out the Q10 transistor was bad but I suspect the lane change switch may have been a contributor. It looks like someone hacked up the wrong type of switch and had the diode connected wrong. The odd thing is that it worked for many weeks just fine but maybe when I took it apart to rebuild the flipper something happened.