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Pinball switch closure timing problem

For years the pinball companies used a small .047 uf capacitor across some switch terminals for switches that could be closed and reopened very quickly like a target getting slammed particularly hard. The capacitor would increase the 'closure time' that the CPU would read the

switch as closed, long enough to help it pick up the switch closure. These switches are just simple two blades and contacts, with one wire to the cpu, the other wire thru a diode to isolate it within the matrix

of switches in the game, and the capacitor may or may not be across the

terminals also.

I'm having a problem with a particular swtich that the cap fix is working, but not completely. Some hardhits will still not register. Tried putting bigger cap on it with improved results but I've read that

too big of a cap can cause 'ghosting' where it might start causing false closure reading on other switches in the matrix. So my question is....

Is there a simple formula where one could increase the size of the .047

cap or .1 cap or whatever is being used, but put in in series with a resistor, to lengthen the time that it is doing it's thing of lengthening of the closure to the cpu? I.e if I wanted to use a cap

10x bigger, what resistor could I put in series with it to be sort of like the smaller cap without the resistor, but length of discharge would be stretched out? Or is this possible? I am pretty good at fixing pinballs, but electronics theory is not my calling. thanks for any assistance anybody can give me. Thanks!
Reply to
frenchy
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Apart than the switch clean (gold contacts, only clean with a business card) and well adjusted, with a good diode and good cap (and good connectors on the MPU), I suspect that there are not much we could do (apart that slightly increasing the cap value as you tried), given that the MPU performs a strobe/scan of switches rows (or columns) at a certain rate and may miss a switch closure if it is too short to be held by the cap between scans. Just my gut feeling.

Have you tried posting in rec.games.pinball ?

Cheers,

- Sylvain in Ottawa, Ontario, Canada

Reply to
Sylvain Gregoire

Another item,

could also be the PIA chip (or its socket on the MPU) for the switch matrix. See my older post in rec.games.pinball for a Bally HotDoggin ...

Good luck, Regards,

- Sylvain

card)

Reply to
Sylvain Gregoire

It would be no big deal if the cap/resistor combination, if it could do it, hold the closure for more than one switch scan. It will not register twice, i.e. it is no problem if the game interprested every hit to this switch to be lasting twice as long or three times as long as it does now, as long as I get a reliable closure I don't really care if it is during one, or 2, or 3 switch 'scans', it would still be doing what it's intended to be doing in the game rules.

Reply to
frenchy

so did you try adding a big cap directly across the swithch?

Mark

Reply to
Mark

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