If things get stronger or weaker over time capacitors are always the first suspect.

If the EOS isn't opening at full flipper stroke, the high power coil will stay energized, overheating the coil making things bind up. Next time your flippers get weak, turn off the game, raise the PF and feel the flipper coils to see if they are hot. Adjust the EOS so it is gaped 1/16" at full stroke. Do not measure by pushing the flipper bat, but by pushing on the pawl into the coil.

I've never played an 80s Williams where the flippers didn't get hot after a while

There's a separate pin on 2j12 going through a separate contact on the flipper relay and down through the playfield connector for each side's flippers.

Are the eos switches new as well? Have you filed the new cabinet and eos switches? I find new switches may need a little filing to get them working properly. How are the eos switches currently gapped on the flippers?

Also, do the eos switch leaves have some amount of tension against each other when the switch is closed? They shouldn't *just* be touching, but they don't have to have strong tension either. You just want to make sure the other switch leaf bends back a bit when the switch closes, giving a bit of a wiping motion.

One other idea: when you replaced the cabinet switches, are they adjusted in a way that fires the upper and lower flippers at the exact same time? Or do the lower ones activate first, then the uppers? It can be in very quick succession, I'm just thinking you don't want all 4 flippers firing at the *exact* same time. Let the first switch close before the second one, even if the difference isn't noticeable in gameplay (and really it probably won't be noticeable anyway)...Honestly, that may not really make any difference here, but if nothing else works it may be worth taking a look.

Beyond that, I've had 2 Black Knight's that saw significant improvement in flipper strength after replacing the male pins and female connector at 3J3 (flipper power and +38vdc for the playfield solenoids) on the power supply board and also 2J12 (flipper ground) on the driver board, the connector zacaj mentioned above. I know re-flowing the solder on the pins often suffices with connector problems, but this was a case where the pins got kind of dull and were creating resistance, which ultimately led to weaker flippers. Only by replacing the male connector pins and female connector pins & housings did i finally get them at a strength i think is suited to the game. (After doing many of the things you're doing/have done so far)

Post a couple pics of the flipper mechs if you like and we can see if maybe getting a few more sets of eyeballs on the matter helps along the solution.

New eos often have a protective coating on them. File or use alcohol, etc to remove it. You'll see the resistance over the contacts drop.

it’s probably a high resistance connection somewhere in the right flipper wiring limiting the current. Check connectors and don’t forget the relay. Also check for burned pins on the boards and reflow the solder on all pins in the flipper circuit.

Don_C

My right set of flippers stopped working when putting the pf’s back in.

The connector at the power board to the flippers was having bad connections to the pins.

I tested continuity of the hardness from the connector to the flippers and magnets. Then repinned the whole connector.

Maybe not the same issue, but you’ll also want to verify the ground strap, continuity and power for the flippers and magnets.

You can file any high voltage switches like EOS switches but don't file any low voltage contact switches. Just clean with strips of cut up business card dipped in alcohol.

I'd reflow every header pin on any board you take out of the machine. System 7s seems to always have bad solder joints.

And I’d check all the connectors pins inside to see if they are going to make good connections. I had two connectors that had to be upgraded to molex as the pins inside were bent or literally not making a connection.