I've had an issue with the left flipper on my Stargate being weak for a few years now, and I've even created a thread about the issue before, but now it's gotten even worse, to the point where I can't make the right ramp shot at all. I've tried everything I know how to do and at this point the issue seems to be beyond what I know how to fix. In an attempt to fix the problem I have

Rebuilt the flipper
Replaced the coil
Replaced the flipper button switch
Made sure solder joints on the coil are solid
Done grounding mods
Made sure the 120V jumper is being used

The flipper is still too weak to make it up the ramp, it doesn't even get close. It used to be that right ramp shots were fairly easy for the first 15 to 30 minutes of play, and the flipper would get weak over time, but now it's just super weak to begin with. The other two flippers seem to have plenty of strength, especially after rebuilding them (The left ramp can be made easily and the ball goes up it very fast) but the left flipper just doesn't feel all that snappy and right ramp shots usually don't even make it to the top of the ramp.

I'm convinced at this point that the issue is electrical, but I wouldn't know where to begin looking to diagnose an issue like that. I'd like to measure the energy going to the flipper coil to confirm, but I'd need some guidance on how to do that with my multimeter. If anyone has any advice, please let me know! I'm not going to stop trying to fix this until the issue is fixed once and for all.

Sorry for not getting back to this sooner. Got busy/stressed with work and mostly forgot about this. I've finally taken the time to look into things and here's what I've found.

Doing this (Red clip on flipper lug, black on ground, multimeter set to 200 V DC) the flipper starts at a little above 70 VDC and then slowly climbs to above 90 after a few minutes. The highest I saw it get was about 98.

The one interesting thing I've found though is that if I test the lug connected to the silver banded end of the diode, and flip, the voltage spikes, sometimes nearly to to 200. The right flipper does *not* do this. Not sure which is normal behavior but it seems I've finally found an inconsistency between the two flippers.

I've tried cleaning the Q relay, no difference (I used the business card method. Should I used something to grind it a bit?). How would I be able to tell if a connector pin is bad or not? How would I figure out which wires are ground for each flipper? I'd be interested in swapping them to see what happens.

Yep, I replaced both the EOS and capacitor. EOS is adjusted correctly. I also replaced the flipper button switches entirely. Game is pitched at 6 degrees.

Final note, while testing today, at one point the GI was off and would flash on whenever a solenoid fired. I power cycled the machine and it went back to normal. Not sure what that was about but figure I should document everything at this point.

Alright, I swapped the ground wires (Both on each lug) and now the right flipper button flips the left and vice versa, so I assume I did it correctly. The switch matrix is also messed up now but hopefully that's just to do with the swapped ground wires and will return to normal once I switch them back.

Unfortunately even with the swapped ground wires the left flipper is still far too weak to make the ramp shot. Would it also be worth trying to swap the other wires (The banded side wires) to see if that makes any difference, or no? If not, I suppose that rules out an issue specific to the power to the left flipper, but it doesn't rule out the possibility that *none* of the solenoids are being powered properly. If all, or even just the flippers, aren't quite getting enough juice the left flipper is the only one you'd really notice it on. The right flipper doesn't have any ramp shots, and the upper right flipper ramp isn't as steep or as far from it as the left flipper ramp. Currently on my game the upper ramp is makeable, but only if shot just right. Otherwise it tends to come back down quite often. I assumed this is just the way Stargate plays, but maybe not.

I also tried using a switch contact file to clean the Q relay, no difference.

Yesterday I found that the center bridge rectifier had a bunch of wires soldered onto one of the lugs instead of connected with a brass connector. I removed the old solder and redid it with fresh solder, no difference. Not that those wires looked related to the flippers or solenoids in any way from what I could make out from the schematics, but figured it was worth trying in case the solder was cold. I also tried reseating all the other brass connectors there, again no difference.

I'm still wondering, is the VDC I measured off the flippers correct? Could someone with a Stargate take a measurement just so I could confirm if mine is the same or not? I'd really appreciate it.

EOS fall under .5 ohms like you said it should. It's basically brand new so it shouldn't have any resistance issues.

Looks good.

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Here's a vid of actually trying to make the shot (The flippers are reversed because I still have the ground wires swapped): https://photos.app.goo.gl/JLNEsZyz2Kbe5J4K7

Today I tried swapping the 48V bridge rectifier with one of the others in case there was an issue with that, and I also tightened up the ground cables from when I did the ground mods, but neither thing made any improvement.

I've considered doing that, but I really want to get to the root of the issue, especially since it seems to be getting worse over time. Using a more powerful coil may fix it for now, but then I might end up in the same situation in a few years.