Can you do a switch test in the diagnostics and report back? And does it light up with any of the five drops being dropped, or just specific ones being the only ones dropped?

Which switch does it report for each drop target? And are you using an original MPU, or aftermarket? If it's an original, I've had serious issues with phantom switches because of battery corrosion; the switch matrix logic area of the board is pretty much in the direct path of battery leaks in the design, and that causes some really odd behavior when it's been corroded.

So, again, in diagnostics, which switch numbers are reported on each drop target?

OK, so no doubling up when one is dropped? No reporting of "30", then "31", then "32", etc, when you drop a single target?

Also, you do have ROM "E" on the MPU?

Here you go. The chips for the switch matrix (they deal with more than the drop target switches) are in the lower left corner of the board. The upper leftmost chip is for the ROM.

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If you haven't repinned the connectors yourself, and have no indication the previous owner ever did, then yes, repinning the connectors is something you need to do. The fingers in the connectors are only rated for something like 30 cycles, and any machine - especially if it saw a route - has a chance of having had hundreds of cycles on the connectors.

Interesting that it's clearly NOT seeing phantom switches, as your pics are showing the bonus ladder, and it's indicating that the machine only sees that you've hit one or two drops. When I was having phantom switch hits, the bonus ladder would move further in response.

Now, here's a question... if you drop a white target and the special lights, does it actually collect the special when you drop the red target? That might indicate whether or not it's a short somewhere in the light matrix causing it to light up when any target is dropped.

That's weird that you're getting that, and no phantom switch action. I'm running out of ideas that don't involve replacing the three chips for the switch matrix control (7404N, 7405N). You might try posting what we've seen thus far, including what you responded with, to the big thread (https://pinside.com/pinball/forum/topic/home-for-the-gottlieb-sys1-sys-80b-guys-yep-i-guess-it-a-club/), or post there to point people here and see if anyone has any ideas.

One other thing to try would be, does it collect the special dropping another white target?

Usually, if there's a fault because of the switch matrix logic, it does something like "walk" all the way along a "column" or "row". What you're seeing is like the MPU is treating one drop target like it's all of them at once, except for the bonus ladder should count up more than one step if that were the case.

If you need a connector to repin, the two leftmost connectors along the bottom of the MPU handle the switch matrix. But it's sounding more and more like there's some sort of MPU logic problem going on. Or some sort of esoteric short in the matrix.

Do you know of anyone that you can borrow a spare MPU from for testing? All the System 1 MPUs are interchangable, all it would need is the ROM. I have an MPU board, but it's badly corroded now and the switch matrix repairs have never lasted before it's back to erratic behavior.

You might also check the diode strips on the underside of the playfield, see if any of those are shorted (both ways instead of one way current flow).

OK. So, the targets work normally, but once you go through the "return to lane" gate, the targets start doing the funky "any drop lights special"? Is there any other impact, like it also lighting (or strobing) the "reset drop targets" lights when you drop any drop target?

That switch (Rollunder, #52), shares the same row (Strobe) as the red target (#32), top kickout (#42, which collects the bonus), the star rollovers (#12), the third rollover lane (#22, lit when bonus multiplier is X3), and the Right Coin Chute (#02). That strobe line is on connector A1J7, line 4, the wire colors are supposed to be Black, Orange, Orange.

First thing to check is to see if the rollunder switch attached to the gate is correctly gapped. It should only be closed when the ball passes through the gate, and reopen once the gate is cleared. It should not close if the ball doesn't make it through the gate - there isn't any real ambiguity, if the ball doesn't have enough momentum to pass through, it won't trip the switch and will be pushed back into the playfield. Make sure the spring isn't binding and holding the switch closed.

Do you have the manual for the machine?

There really isn't a difficulty setting on Solar Ride that changes how the drop targets behave. There is only 3/5 ball (which only changes number of balls, whether Extra Bonus adds 3 or 5 to the ladder, and specific score of the bumpers) and Replay/Extra Ball (which changes what the award is for the Special and score tiers).

It sounds like a hardware issue to me. I have a Solar Ride (it's our only real pinball machine currently), and when the switch matrix gets funky, it does some really odd things that seem like they might be rules settings gone off.

There is a slight chance if the ROM has gone bad it could cause an issue... the problem is that it's difficult to source a replacement because of Gottlieb's holding company insisting that everything for repair - machine specific manuals, software, parts numbers - must be purchased from a licensed seller or by finding bits for sale from existing machines.

I know there was a place that sells ROM chips for System 1 when they get them in, but I don't rightly remember which one; we'd already made the choice here that, when it came to that, we'd go for an after market board. We bought a LISY1 for ours in 2018.

I'd second using the heat sink, but use a proper thermal tape to attach it - most heat sinks you buy for this sort of work should come with that tape. Regular superglue will fail when exposed to heat. My recommendation is to buy a set for use with the Raspberry Pi, that should get you a heat sink big enough and the matching piece of tape.

You're welcome. Glad it was ultimately a simple fix.