When the motor runs, the switch opens.

Just a WAG here (really asking Ken more than anything else), but I think the "O" is a 'zero', based on the other one you circled that has a '5' next to it. Probably a index number for the contacts?

Then another WAG: no diagonal line is 'normally open' whereas one w/a diagonal line is a 'normally closed'?

Pretty sure it is an "O" not a zero. May be reflecting the state of the switches given the score motor position as the schematic is drawn.

The Williams Score Motor annotation is a little confusing and sometimes inconsistent. They did however publish at some point a decoder ring:
Williams score motor cam switches (resized).jpg
The helpful intention is that the switch label is supposed to give you some timing context which should make unwinding a circuit involving a score motor sequence a little easier. So for example a switch labeled 2A (on cam 2) will close momentarily before any switches labeled 3A (on cam 3) or with any higher number. When they did it consistently on a schematic it made things clearer than Gottlieb's notation for example (where 2B happens after everything else). Unfortunately I think these labels were sometimes inconsistent which made things a little worse.

Williams schematic symbols (resized).jpg

These diagrams are from Williams' Intro to Coin Operated Amusement Games available here and other places:
https://archive.org/details/introductiontocoinoperatedamusementgames

/Mark

I've seen similar issues with O and C score motor switch labels and don't have a good explanation for that, hence the inconsistencies I mentioned earlier.

I don't know. Sometimes the schematic will tell you something about the state of the machine, but often it won't, or it will only give you clues like this:
Williams schematic note (resized).jpg
If you're lucky, maybe there won't be any active relays when the game is reset but not unplugged so it won't matter.

Hi paulace +
because there is a topic running in a german forum I plan to open up here in pinside a topic "faults in schematics / manual - Fan-Tas-Tic". Funny - Your last sentence in post-8 --- reading Williams schematics from the 1970ies: I simply not pay(ed) attention to these "O" and "C" --- maybe grumbling
- "I see from the "diagonal line" drawn through the switch: The switch is closed, I see it is a Score-Motor-Switch - therefore when the switch will be operated, actuated - it will OPEN --- I simply do not look at the "O".
- " I see from the absence of a "diagonal line" ...
- I see from "IMP." at the drawing that the switch is mounted on the Impulse-Cam of the motor --- there always are mounted 5 teeth on a turn of 180 degrees - O.K., I see written there "5" - who cares.
MarkG - thanks for the link in Your post-7 and the JPG (from the document) --- maybe (?) useful on early schematics on pins when they had the old Score-Motor (looking similar to Gottlieb Score-Motors).

I accept the naming of the Score-Motor-Cams "IND 1 2 3 4 5" as "telling when operating in a turn of 180 degrees - IND is the cam having actuated its switches in Home-Position, cam-1 will actuate at "30 degrees (((one times 30))) ", cam-2 will actuate at "60 degrees (((2 times 30))), cam-3 will actuate at "90 degrees (((3 times 30))), cam-4 will actuate at "120 degrees (((4 times 30))), cam-5 will actuate at 150 degrees "(((five times 30)))".

I look at Williams, Bally, Gottlieb schematics assuming "a game has been started for one player - all the reset stuff has been done, ball has been kicked over to the shooter alley - then pin is toggled-off and / or line cord unplugged".
I never could look up in a Chicago Coin machine - from the schematics (see the JPG) I assume "a game has been started for one player - all the reset stuff has been done, ball has been kicked over to the shooter alley - AND then the pin stays toggled-on and line cord plugged-in".
Greetings Rolf

0Sound-Stage-Work-02 (resized).jpg

Thanks for pointing that out. I had overlooked that. Now I wonder if Bally ever specified how their schematics were drawn.

I combed through all of the technical manuals I could find while preparing materials for my class and have posted snippets in the forum like the one above that folks seem to appreciate. If that makes me a nerd I'm good with that. While going through that exercise I discovered that big chunks of the manuals from two of the manufacturers are word for word the same which makes me wonder who actually wrote them.

I recently ran across this nugget on the Williams Skill Pool schematic on ipdb.org:
Skill Pool Motor switch nomenclature (resized).jpg
I think the position of the movable part of the switch (above or below the 2nd contact) also is meant to show NO vs NC switches.

This game (Skill Pool) uses a 2 cam score motor with a vertical shaft that looks more like a Gottlieb score motor. There's a complete diagram of it on the schematic. The position referred to above indicates which switch stack the switch is in. I suspect though that the number also indicates the relative timing of the switches just like it would on a horizontal shaft score motor with multiple cams.

These are normal 2 leaf score motor switches. The first is Normally Closed and the second is Normally Open. Note that these symbols are rotated clockwise 90 degrees when they're used in the schematic.

The schematic has lots of other interesting symbols that take a little detective work to sort out. Here are some examples:
Skill Pool Motor schematic symbols (resized).jpg

It seems like the point is to indicate what the switch does during the course of the score motor rotation (stay open, stay closed, pulse once on certain angles, pulse multiple times, etc). The first example on the image linked above seems incorrect - it should be ‘C’ to indicate it’s closed during the rotation.

That being said, I have no idea why the schematic snippet you posted shows a NO motor switch with ‘O’ by it. If that’s not just a single typo instance, then maybe that’s just how they labeled them instead of using ‘C’ (even though it seems completely counterintuitive).

Now I gotta go check my Space Mission schematics to see if they have this too ..