Normally, hitting one of the Left or Right Stand up Switches pulls in the 500 pts Relay which in turn starts the Score Motor and thru Switch A on the Impulse cam fires the 100 pts Relay 5 times to jog the current player's 100's Score Reel.

However, on my machine, the No3 Reset relay also fires once immediatly after the 5 impulses. This cause, thru the Score Reel reset circutry, all the not-at-zero 10,000s and 100,000 scores reels of all players to jog once!

Have a look at the couple of videos below.

This one shows the score reel action when player 2 scores 500 pts. You can see all the other players non-zero score reels jump up one digit after the 500 pts is scored for player 2:

https://photos.app.goo.gl/LKAmc6g1esjkVi8x9

This second one, you can see the 100 pts Points relay pull in 5 times and then the No3 Reset relay pulling in once:

https://photos.app.goo.gl/mVzk7DCAxNhfxpJ96

I beleive I can logically eliminate a few suspect such as the Coin and Reset Realy switches cuz if they were closing for some reason, The No1 and No2 Reset relays and the Playmeter would also fire. Not the case.

I did test that out anyway by dropping cardboard strips in all switches that could provide a power path the the No3 Relay coil to energize it:

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i) One in the Score Motor Impulse switch B (in red) located immediately before the No3 Relay coil which indeed stopped it from firing. Believe that eliminates intermittent short between that switch and relay coil.

ii) Then in the Reset and Game Over switches (in yellow). They are in parallel and located just before the Impulse Switch B. That did not stop the No3 Reset relay from firing. So I believe this would point to some kind of short between those two switches and the Impulse switch B.

All these switches are on the cabinet insert. So I cant disconnect any Jones plugs to do any continuity tests to ground or something.
And i may very well be missing something else.

Any suggestions out there?

Added a couple close up pics of the relays.

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sch01 (resized).jpg

(P.S. I don't know why the schematic pic appears twice on this post, I've inserted it only once. Plus this line of text was placed after all the pics. Arghhh..)
Back 02 (resized).jpg

That seemed so probable to me that it made me reopen my shop just to verify that....

Could no see any shorts. Spaced the tabs better just in case. Checked for stripped wires touching. None found.

Powered up and tested. No go. Same issue.

Tomorrow, I'll take a good look at all switch tabs on that SM. See if I can find anything.

Keep the ideas coming.

Thanks

Checked all tabs on SM. Inspected them properly.
did not find any shorts. Adjusted them all regardless.some were pretty close.
But no luck.

Checked the tab at the two other switches that Blu-W wire connects to.
No luck there either.

I spotted the same behaviour when scoring the bonus.
But not when scoring spinners or pop bumpers.
Don't really seams that the behaviors only occurs when scoring involves the score motor.

Will keep looking...

Good idea, I will run the SM manually.

In the mean time, I've done more research and stumbled on this topic form 6 years ago by pinsider rufessor

https://pinside.com/pinball/forum/topic/grand-prix-random-10000-and-100000-score-advance#post-1660306

He had the EXACT same issue as I.
He even found that the issue goes away when the AB or the CD targets are hit. And returns when moving on to next player.
I had not noticed that behaviour but was able to verify it consistently on my machine. It's totally repeatable.

The unfortunate thing is that in the end, after a ton of trouble shooting, the one thing he did was to dismantle and reassemble the IMP switch stack and the problem disappeared. Arghhhh... He never really pinpointed the problem. I'll try that, but I'm sceptical that was the actual solution.

I'll certainly try to find the relation with the drop target circuit.

Kowing now that another fellow had the exact same issue, that the issue appears without fails in the very same repeatable conditions tends to make be believe it may not be a spurious short somewhere. If that were the case, I believe the problem may likely not be so repeatable.

Adding to the weirdness of this is the fact that in his topic, rufessor also talks about another sporadic problem he has with his machine (Bonus unit not always stepping up one step after a total reset). I also have that same very sporadic problem. It is really weird that this guy had all same issues as I do. He does mention what he thought the solution was to that problem (an improperly gapped switch on the alternator relay), but he doesn't believe it was related to the scoring problem as that one was solved before he solve this one.

Well well well, here is something. Can't say if it's related or not.
I just discovered a discrepancy between the schematic and my machine. But I think it's factory.

I was scrutinising my score motor and found that switch stack on cam 3 on my machine has one more switch than on the schematic.

See pics.
(Yes, I am looking at the right cam. Cam 3 is the one right after the long dwell, shown in the foreground.)

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Anybody have an explanation for this?

(Oh BTW, this does seem to reveal a gaping problem with the switch D but that's just because the cam follower is already partially riding up the cam.)

Not really the case here, but a failed insulator can still be the culprit. So I'll certainly be looking at that.

You beat me to that one. I thought that might have been the case as I was laying in bed last night night thinking about this. Got up this am to verify and saw your post just before.

But there is still a slight discrepeancy as the stack has only one MB switch and the schematic shows two. Thinking one of the two shown in the schematic may only be connected on one of the throws?

In any case, we may be going down a rabbit hole. Don't think it's related to the issue at hand.

Moved one step ahead on this in one.
As suggested, I operated the SM manually after scoring 500pts.
And I found that the it's the cam 5 switch stack that activates the No3 Reset relay. The cam follower drops into the cam 5 notch just an instant after the 5th and last pulse of the impulse cam and that is exactly when the No3 Reset relay pulls in.
So to figure out which switch of the stack was causing it to pull in I held the switches up over the notch of cam 5 and let them drop one by one. This allowed me to pinpoint the switch responsible for activating the No1 Reset relay. And it turns out it is switch 5A (circled in red). I confirmed this by repeatidly opening and closing that switch and seeing the No1 Reset relay pull and drop consistently. Wow... That switch doesnt even come close to being related to the No3 Reset relay circuitry....
Moreover, looking at that switch's circuit explains why the problem disappears after hitting AB or CD stand ups. Hitting any pair of stand-ups energizes the No1 Star relay. Which opens the switch in series with 5A (circled in green). Until that relay drops again for the next player or ball.

So this would further pinpoint the problem (a short?!) as being downstream of that No1 Star relay switch... I think?!
And also probably upstream from the L and R Bonus relay switches... Maybe...

20210125_212113~2 (resized).jpg

Hum...

@MarkG: I was looking at that cam 3 switch stack and schematic. Im.pretty sure the two switches you have highlighted are really the same ones! Both throws of he same MB switch. They actually share the same common wire R-G.
So really the error is that the one labelled 3E should really be labeled 3D.

So we are back at my initial question: what is that 5th switch in my cam 3 stack?
And it looks like a NO switch between the C and D. With a Y and a R-Y wire. All the other wire on the other switch match the score motor documentation.

No, it fires when the switch 5A hits the notch of cam 5. This happens just a tad after the 5th impulse of the Impulse cam. The 5th impulse itself does not energizes the No3 Reset re.

No questions just yet but maybe tomorrow or the day after when I get back to my shop. Time for bed now. Gotta get up bright and early in the morning.
Thanks for the offer.

Ah yes! That could be it. I have to resist going back to the shop to check this now...
I'll let you know. But that would point to a faulty switch stack insulator people have been hunting at.

On a side note, what do you think of that new information regarding the extra-switch-on-cam 3 mystery?

Impulse switch stack...
20210130_171258 (resized).jpg

Can you see it? It was staring me in the face he whole time. Can't believe I missed that.

This stack is the only one that has no insulating papers between the switches. I can't figure out why that would be. rufessor mentioned this in his topic also. He very likely had the same problem as I did.

Anyway, the machine works flawlessly now. It's been a long restauration.

Thanks for the troubleshooting help.

A few pics to close this post.

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