Hello Guys. I've had this Williams 1970 "4 Aces" for approx 3 years and now finding the time to work on/restore.
Taking the advice of many of your post and others, I spent about two weeks disassembling all the indexing units.... ball count unit, Replay unit, player unit....ect to insure they all indexed/reset smoothly. All of them had gummed up residue "I assume WD40" but managed to get it all cleaned up and working like they should!
I also cleaned every contact on the machine with my wife's soft flexible 320 grit nail pads and rubbing alcohol. I made no adjustments to contacts, waiting till everything was cleaned up to see how it started up before anything else.
During all that I found one flipper EOS limit switch broken, bad coil on special bonus indexer and of course 23 - #44 bulbs burnt out.
All of that was replaced.

Okay my problem... Turned the machine on and she lit up and was quite.
I put a quarter through coin slot, the "replay unit" indexes and registers 2 credits.

When I press the start button:
Both of the player score units index and zero's out.
"In lower cabinet" The reset unit indexes the lift bar that resets all the game play relays at once.
Game over light goes out.
Player one and player two lights jump back and forth a couple of times, then it stays on player one.
Game ball one lights up.
One credit is removed.

"All that seems normal"

The problem is, the machine goes into continuous cycle of:
"score reset" relay is doing a triple tap of contacts every couple of seconds continuously.
"Ball unit" reset solenoid is being triggered every couple of seconds continuously.
and the "score motor cam" never stops cycling through complete revolutions.

I tried many times to turn the machine off and check for obvious problems or indexing units not resetting with no luck However, JUST Once of of the many times I restarted the machine, it actually stopped cycling and allowed me to play one ball till I lost. Now it's back to the same problem with one exception. When I turn the machine on now. In addition to "Game Over" displayed, it also has "Tilt" displayed till I hit start button.
I can read schematic's and am trying to go through it but as most are aware "experience" usually leads you to the right place to look right away.
So asking for suggestions of where to look.
Thanks in advance for any suggestions! Attached schematic below.

4Aces pic (resized).jpg

Playfield (resized).jpg

Williams_1970_4_Aces_Schematic_Diagram_continuous.pdf

back panel (resized).jpg

lower cabinet (resized).jpg

@ MarkG Thank you, you are correct and I have been tracing back all the relays/switches that in gauge the score motor. I've narrowed it down to a small section with 4 possibles: Ball unit 0 break, Game over, 8 Drum unit 0 break or score motor index. The Ball unit and Game over contacts, I put paper under contacts but it continues, so either 8 Drum unit or "score motor index which is not likely".

@ Black_Knight thank you for responding!
I read through most of your post and yes, it sounds just like my issue. Had to take a few days off to quit pulling my hair out "what's left anyways". Going to look at same components today as in your post and report back what I find.

Quick question; on your post HowardR posted a pick of schematic section, exactly where I was looking on my schematics but I'm unfamiliar with the "Drum unit". On my schematic it actually says "8 Drum Unit" and is only mentioned once on schematic and nothing in the manual. Could you tell me what it's referring to?

Thanks again to you both!