Buy a metal stern bob and try that?

Sorry guys, I don't get on Pinside that much anymore. Definitely contact me at [email protected] with questions like this. Jeff did yesterday, which is how I realized this thread was going on.

Tilt unresponsive: this is common, the switch is a graphite bob on one side of the contact, and a brass ring on the other. It is nothing like the gold-plated contact switches through-out the game, and is not going to last 40 years in operation as we expect it to. The transmissivity of the contact is just not there, so getting the contact to drive the strobe line to '0' volts is going to need some effort on our parts. I like the idea of the Stern metal plumbbob, but haven't tried it, and Marco is out of them. So last night, I took steel wool to the graphite bob, *and* the brass ring (and even the area where the metal rod contacts the tilt frame). On my Sinbad, it made a world of difference, though I'd say it still missed 1 out of 4 "hits". My bob is pretty "dinged" up along the graphite from hitting that ring, so I'm not too surprised.

There is likely nothing wrong on the board guys, and no chip/diode you can change to address this, unless you want to mess with every switch on the front door (these are the common return line switches). If your game start button is working than your chips are OK.

If someone *does* have a metal bob - I'd be interested in hearing the results.

-Ace

As noted in post #16 of this thread, the pull-up resistor on the switch return line the tilt switch is on is 1k ohms (Gottlieb boards have a 2.7k ohm pull-up resistor). This doesn't help a resistive plumb-bobs cause.
Is there any reason a higher value pull-up resistor (say 10k ohms) couldn't be used to make it easier for the plumb bob to pull the signal to zero volts on fast activation?

To add to this, although I'm not sure if it's relevant here: my LISY board had issues with many standup switches too. No matter how close I gapped them and how much I cleaned them, they wouldn't register consistently. I've since repaired an original gottlieb MPU and installed it, no more issues with the standups, and the tilt seems more sensitive.

I'll see if I can measure the strobes on the original MPU and maybe the LISY too for comparison... I don't have direct access to any Ni Wumpf MPUs though

Update:

original MPU scans all columns at 60Hz. pasted_image (resized).png
It does a weird double pulse consistently, not sure why, but I guess that winds up as a 3ms pulse width? pasted_image (resized).png

Remember Quench - this is an active LOW signal. A lower pull up value on the return is likely to help reactance - not the reverse. So no, a 10k pull-up would be going the wrong direction - especially if there is any resistance in the contact surfaces. It'll help the recovery signal, so that you can strobe faster, but that too is not the intent.

-Ace

Wait, but isn't a higher value pull up weaker? So if the bob is trying to pull the signal down (since it's active low), the weaker the pull down, the lower it will go, which should make it easier to sense? You said in your email that the problem was that it was having trouble driving the signal to 0 due to the bad connection of the bob-ring, not an issue with the pulse length?

Respectfully, I don't see your logic here.
If the plumb-bob is having trouble pulling the signal LOW because of resistive contact, then a *higher* value ("weaker" as zacaj put it) pull-up resistor will allow the signal to swing low easier.

The question is whether there would be any side effects of raising the pull-up resistor value, i.e. will the R0 return signal accidentally trigger on noise interference through the cabinet/playfield wiring harness?

Out of curiosity, can you explain the Ni-Wumpf software logic to determine a "valid" tilt switch activation? i.e. how often are switches scanned, and how long do the switch return signals need to be active LOW to be considered a valid switch activation and not just noise/switch bounce? Or does your software switch matrix scan method work differently? (I come from the Bally world)

With the lower 1k ohm pull-up resistor being used, shouldn't the C7 "switch settling" capacitor be raised in value to hold an activated low signal longer?

Gents, in a series circuit, where there are two resistors R1 (the pull-up), and R2 (the resistance of the contact at the plumb bob from bi-metal contact), the higher the pull up resistance (R1), the greater the voltage drop will be measured (whatever the current) across that part of the series network. So in the conductance case, you'd be right, with all that voltage across R1 (especially if we pull it higher), the lower the signal would drop as measured across the contact (R2). This would be good, as you guys describe.

But we are not seeing "contact", and the reason isn't the voltage, it is the *width* of the voltage pulse (zacaj' picture above is, after taking away the double pulsing, pretty generous. The normal pulse is 15 - 40 mSecs active-low depending on the board) . We are trying to increase *reactance*, not conductance - the inverse of capacitance across that contact. Which means we hope to pump current across those contacts to overcome whatever the RC value of that contact is (lower the pull-up resistor). I can't change the filtering capacitance on the input circuit on the board, or when you press the start button, you'd register more than one "game start" request occasionally. So I have to change the 'Q' response of the contact during a pulse (skip the rest of the parts of that equation that I cannot change, like chokes and crap) - to do that, I have to pump more current: i.e. lower the resistance of the pull-up, and hope that the resistance of the plumb-bob contact is still minimal when compared to a 1K pull-up. When you think about it, at what point would it make a difference if the pull up is 10K or 1K - probably right around 100 Ohms contact resistance value. I don't think that this is the case, so I doubt that we care about the resistance of the pull-up.

Having said all that - it's a crap shoot. At design time, you start somewhere, put a scope on the signal (with capture), set your scan frequency, and see what the return signal looks like as we tweak the return capacitance / resistance values, coupled with the strobe signal pull up resistance. Fun huh?

Now, to answer the question: on the original board, we did logic debouncing of a contact - in other words, a valid switch is identified after 3 active low pulses are received sequentially on the return line from the same strobe line at the 8279. That is not normal for a pinball CPU, but at the time, I was into acoustics, and a purist, this was how we did things to be absolutely sure that transient signal spikes from the rest of the game were not being seen on the return circuits showing false signals. In 1995 it worked great! Even for the plumb bob (or so I thought then with the game I had) It was partly this circuit design that allowed us to really improve spinner target response. We could detect spinner closure 2 - 3 times the amount that the original board could, and this was one of the odd goals we had (remember the reactance spiel). With the new board, we tried conditioning the return pulse with a more complex circuit (check the schematics between the 2 boards), and do away with switch debounce. Embarrassingly, that worked just as well, and the response seems about the same. It cost more, but the return circuits were pretty much bullet-proof - you could short a coil voltage to the returns, and not blink (though, that would probably take out the strobes).

Now, how fast are they strobed? I can look it up, but remember we are strobing the displays at 2X the speed of the switches. We need to fit 8 strobe lines into one full strobe "cycle". Whenever I change the active low pulse width, I also wind up changing the width of the full pulse cycle on the displays. I think the default width is 15 mSecs as I mentioned above - the original board used closer to 40 mSecs active low, which will definitely help improve switch detection of the plumb bob, but then you've lost your spinner response, (and overall playfield response feel).

Now, you can change this on the new board: set the options to EXPERT mode and tweak the switch strobe speed. It shouldn't affect the game - though it might make the displays a little less crisp. Don't go past 40mSecs. This will help the plumb bob response, by reading the signal, hopefully after the reactance curve falls to the acceptable level, and won't affect the front door switches.

In the end, everything is a trade-off. Electronically, you get fast game play, or a good plumb bob. If you want to run a System 1 tournament, clean the bob, and the brass contact ring, you won't be disappointed, if that is still not great, set the switch strobe speed higher, and put the game into Tournament mode. Sorry, this isn't an option on the older boards.

-Ace

Thanks for the explanation Ace,
I have no experience with Gottlieb in this regard as I'm from the Bally world. They require active high switch returns which seems the better approach and gives more margin to sense active TTL switch signals, but that's another matter. They use 56k ohms pull-down resistors with no switch smoothing caps on the MPU board - these caps are fitted directly and only across fast react switches (tilt mech being one of them) with a value of 0.05uF - hence the O.P asking about installing caps on the Gottlieb tilt switch plumb-bob mech.
Bally scans the switch matrix every 8.3ms. Each strobe line is active approx 257us and the switch returns are read at the 238us mark. Two consecutive active high signal returns on a switch are then considered a "valid" closure. The switch has to be serviced then sensed as open before it can be validated a new time and this works very well. I don't know if you're handling debounce in software or via the 8279 keyboard mode.

With the tilt plumb-bob closing/opening instantaneously unlike the swiping action of all other game switches seems to me makes it difficult to sense sequential closures in this scanned matrix circuit. With that in mind, if someone was to design a circuit to sense the plumb-bob activation and have it simulate a longer hard switch closure, what's the optimal time of the active low pulse you want to see?

couldn't you just add a cap to the plumb bob to draw out the signal longer so the board can see it easier?

I don't think anyone in that thread actually said that a cap won't lengthen the pulse? I'm not seeing one offhand. It's not helping in your case, but is there really an electrical reason why the cap doesn't lengthen the pulse here? I don't know of one, and the fact that this isn't helping suggest it's not a 'length' issue to me...

I'd love to actually get a scope on your machine and see exactly how long the pulse is lasting, if a cap effects it, and how low the voltage is getting during that pulse...

DoverPros seems to have said both ways, so I'm confused on that end. Is the issue that the pulse is too short, or the issue is that bad contact isn't pulling the voltage down enough?

Sorry not me, I don't have any system 1 games to test it on.

In the meantime, I still think the diode/cap has some merit, *but* a 1N4004/1N4148 diode isn't going to cut it and neither is a 0.047uf capacitor in this circuit.
The logic low level for a TTL chip is considered between 0 and 0.8 volts. The MPU board wants to see the active closed switch signal in that range for a period of time.

A low current voltage drop across a 1N4004/1N4148 diode is approx 0.72 volts leaving you next to no room and that's assuming the MPU board manages to pull the strobe line down to zero volts.
That's the reason I asked if you had a 1N5819 diode. The low current voltage drop across them is about 0.25 volts giving you more headroom before the signal upswing moves into the indeterminate logic level voltage.
The 1k ohm pull-up resistor on the MPU board will charge a 0.047uf capacitor too fast rendering it useless in this application. You might need something like a 10uF cap to hold the closed switch state longer.

But I'm only guessing - not sure I can add much more here since I don't have any games of this series to experiment with.

Disconnect the strobe wire from the tilt mech.
Banded side of the diode on the strobe wire.
Non-banded side of the diode to the tilt mech where the strobe wire was connected.
Capacitor across the two contact points of the mech.
If you're using an electrolytic capacitor, connect the negative lead to the non-banded side of the diode.
Identifying the strobe wire is the one that does NOT connect onwards to the coin switches and start button.

Hopefully this helps, if not something more fool proof needs to be done.

Update from arcade owner is that his all have pascal boards, and they all tilt. He will be setting up another game in a couple weeks and putting a NiWumpf in it to check out its response.

If the switches are active low as Ace says adding a cap will do nothing to lengthen a low pulse (it would make it shorter, if anything). Seems "backwards" to me, if the normal state of the switch is high, so the pulse is low. I wonder what the design philosophy behind that was?

Confirmed that my Joker Poker + Pascal tilts no problem.

Aren't most games active low? WPC at least, I think sys 3-7 too? On my homebrew I found it helps with avoiding stray switch activations from induced current from nearby solenoids

The strobe being low is what I mean. Maybe most games are - I thought Bally sent a positive pulse (I guess any multiplexed PIA would have to?)
Is it easier to detect a low or a high pulse vs. noise?

I have joker poker with pascal as well. Also tilts no problem. As does my count down with pascal.

Great to hear! thanks for the update

see the cap method did work. With an altered addition.

Glad this helped get the tilt working properly.

The instructions should be included with each Ni-Wumpf system 1 cpu board.

Great job guys!!! I sold my Sinbad to a good friend. I'll put together a kit for him. My Joker Poker is working fine with the electronic tilt, but if I ever sell it I'll put the plumb bob back in and keep the electronic tilt.

Impressive engineering by Quench! I can't believe I watched this solution come about in real time. This is what makes Pinside awesome!

Probably should get a write up perhaps even with a drawing and have marked as key post. I will be ordering parts with my next order.

Annotated pictures would help.

can we get a photo? thanks!

MLCC type capacitors now-a-days are pretty impressive in size to capacitance/voltage rating. It would be a 106 cap code.

This should also be added to the PinWiki site.

Any tips on getting Ace to respond to email? Same board which is acting dead. I need to know if it is gone or I can mail it in, etc. No responses at all. been 2 weeks.

You can see the thread I created here: https://pinside.com/pinball/forum/topic/ni-wumpf-system-1-cpu-v1-board-issues#post-5754534

I really appreciate the effort made by JethroP and Quench. I went ahead and disconnected and removed the prototype electronic tilt board from my Joker Poker and reinstalled the good old plumb bob. I used a nice new plumb bob with thumb screw from PBL along with the new diode and capacitor. The tilt now works perfectly I am glad to report. Now if only the foam ear plug trick would work on these old Gottlieb games without replacing the plumb bob hanger and shaft...

I like the original tilt mech better than the electronic one for a number of reasons. The electronic one worked just ok, but the software was in a very early stage and needed a lot of work to be a really good replacement for the plum bob. Being a beta tester, I wrote up a long list of things that I would change and sent them to the person who is designing the board. Unfortunately I am not sure he is still working on this project as I have received no response.

Edit: Here are the parts I ordered. Diodes and capacitors are literally a dime a dozen, so I figured I would order cheap assortments that had the proper values in them. This will give me enough to do a bunch of games and who knows when I will need some other diode or cap for an old Bally game or something? Anyway I found a diode assortment for $5 shipped and caps for $10.

https://smile.amazon.com/dp/B01M7S2ROI/ref=cm_sw_em_r_mt_dp_U_CfAhFb0S67GFP

https://smile.amazon.com/dp/B085RDTCCV/ref=cm_sw_em_r_mt_dp_U_VjAhFbBCCTVF5

Those are good prices on those assortments of diodes and capacitors.

I had the same issue when using the Pascal PI-X4 board in my system 1 pins.

I tried the 10UF cap paired with the NTE585 diode and it tilted upon game start.
Soooo....
I modified the spec to a 2.2UF electrolytic I have good stock of and SUCCESS!!!!
It is just as sensitive as any Bally SS now.

So 1N5819 (NTE585) paired with a 2.2UF Electrolytic did the trick.(Pos side of the cap soldered to the non banded side of the diode)Will be doing this to the rest of my System One pins.

Hats off to you Quench and thankyou Jethro for starting this System One tilt fix discussion.

Cheers!
Dr. Dave