SYMPTOM
Sometimes I lose power or get partial power to flippers and/or the two maze kickers -- I don't think I've seen the pops, drops, or the slings lose power even once. It's happened off and on pretty much since I got the game. I can go 10 games with no issues, then the problem comes back. I can turn it off a while, then on again (didn't count the time interval to imagine heat changes) and then it might work fine again for a few games.

OTHER WEIRDNESS
kinda loud hum in attract mode *before* you start a game after first power up.

WHAT I'VE DONE
* reflowed SDU-100 header pins
* added 3 grounding mods to back of SDU-100
* verified solenoid fuse and under-playfield fuse have continuity out of socket (replaced playfield fuse for good measure)
* tried jiggling all 5 SDU female connectors while flipping flipper that is dead (no change) -- but only tried this once
* Disassembled both maze kickers and cleaned em.
* swapped in another SDU-100 to verify that the problem in fact goes away (which at least eliminates female connectors + other boards and fuse clips)

WHAT I HAVE NOT DONE
* measured TPs while in a good or bad state

REFERENCE
https://www.pinwiki.com/wiki/index.php?title=Bally/Stern
http://techniek.flipperwinkel.nl/ballyss/rep/index1.htm
https://pinside.com/pinball/forum/topic/vids-guide-quick-bally-driver-board-repair-bulletproofing/

READING
https://pinside.com/pinball/forum/topic/stern-pinball-troubleshooting
https://pinside.com/pinball/forum/topic/flippers-dying-mid-game
https://pinside.com/pinball/forum/topic/strikes-and-spares-solenoid-power
https://pinside.com/pinball/forum/topic/bally%E2%80%99s-hotdoggin-solenoid-issues
https://pinside.com/pinball/forum/topic/how-to-test-flipper-relay-on-solenoid-board-ballystern
https://pinside.com/pinball/forum/topic/classic-bally-flippers-not-working-stumped
https://pinside.com/pinball/forum/topic/bally-eight-ball-outhole-kicker-not-working
https://pinside.com/pinball/forum/topic/stern-meteor-flippers

Here's an example of the maze kickers working on partial power. Both kickers were disassembled and cleaned to eliminate drag as part of the issue. And again, it's an intermittent power issue not friction/drag.

They tend to go together.
Yes I cleaned the maze kickerss. (Added above)
Did not touch the flipper enable coil -- which is what?

I'll swap SDB's and reflow the relay and report back.

I can't help but wonder about the clue where kickers/flippers go low power -- but not the drops/pops/slings. Wouldn't that point to something?

Re flowed flipper relay. No change.
I can get power loss 3 minutes into playing a first game.

What do the two kickers and flippers have in common that the other solenoids do not?

Swapped in a new sdb. Sure seems like that's the case.

Cannot reproduce error now after 30 minutes of play.

Interesting that the loud hum is still there in attract mode.

What's a possible next step for troubleshooting the old sdb?

I'm looking in the user manual -- what is the difference between "momentary solenoids" and "continuous solenoids" ? -- it appears I am just having intermittent low power issues with the continuous solenoids.

A friend gave me a hint. Check for good ground. I cleaned up pins 23, 24 with an eraser -- on j3. I'm 10 minutes in, so far so good. Fingers crossed.

That's a wrap. J3 male pins up for re-pin someday...

I think I have a backup set of new caps here from big daddy I can swap out.

Which set would you start with? I prefer to change things one at a time rather than shotgun all 5. I have a chance to find cause easier, and learn more that way.

It's funny as far as hum goes, this is my only B/S with hum.

I have hum in 66% of my sys11s + sys9:

Diner, Taxi, Grand Lizard, High Speed, Space Station, and Sorcerer. (but NOT in WW, Pinbot, Space Shuttle)

oops I replaced the 5v ripple cap on the sdu-100 haha. funny stuff. Still good to do!

One sec! I think I have the sound kit too...

Looks like the previous owner took care of it? Or are those originals...
20220709_f2k-sound-board-caps (resized).jpg

https://www.bigdaddy-enterprises.com/repairkits/stern_kits.htm#SB-300

I'll open a new thread for it someday when I choose to chase it down. I think the game is playing a tone and it's low and sounds like a hum -- there are certain parts while playing when things get quiet, and I hear the low hum tone again, and then it's gone rest of the game. I don't think it's just pure line hum. But that's just me guessing.

thanks for the cool idea -- I need to make a movie for you, so you can decide whether it's a tone or a hum. I'm leaning towards a tone at this point.