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!

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


"frenchy" wrote in message
oups.com...
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!

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

"Sylvain Gregoire" wrote in message
...
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


"frenchy" wrote in message
oups.com...
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!

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.

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

Mark