TECH: Twilight Zone (TZ) repair notes
sinkva
Hi. I'm new to RGP. I recently got a Twilight Zone from Ron Kral
(after he and his daughter had shopped it completely). I'm totally
thrilled with it.
Ron and I also spent a couple of weekend mornings fiddling
with/adjusting my Twilight Zone machine, and he said that I should post
my fix/repair notes on RGP. So here goes...
===========================================
Problem: After warming up, the top/upper left flipper was weak (or
didn't flip at all).
The fix for this was a two-parter. The first part of the fix was to
clean the flipper optos. A blast of łDust Off˛ resulted in a huge cloud
of dust coming out of the optos. That got rid of the łworks OK until it
warms-up˛ behavior of the upper left flipper, but the flipper was still
not working quite right.
Most of the time it would flip OK. But sometimes it would flip half-way
out (then kind of buzz). Sometimes it would flip out, then collapse
back (even though I still had my finger on the flipper button).
Sometimes it wouldn't flip at all.
The answer is in the optos themselves (original, vanilla, stock, as far
as I can tell). There's a basic weakness in the design of the
Fliptronic-II board when flipper optos are connected to it: there's no
hysteresis designed into the comparator circuit (the LM339s). If
electro-mechanical switches are used with the Fliptronic-II board, then
that's not a problem. But when you use optos (like in TZ), the design
of the flipper opto switches allows for a continuous range of voltages
to be sent to the input of the LM339s on the Fliptronic-II board. If
you have a light touch on the flipper button, the
light-touch-flips-the-bottom, heavy-touch-flips-the-top behavior of the
flippers can contribute to funny top flipper behavior.
But I digress. A couple of things to know: 1) the LM339 comparators are
trying to do their job in an incredibly noisy (electrical) environment,
and 2) the current going through the opto (probably the saturation
current, but I haven't checked the specs) can be as low as 7mA when
fully illuminated (when the metal blocking the IR transmitter is
completely moved out of the way by the flipper button).
So what? Well, say you press the flipper button all the way in. And
your opto current is only 7mA. That makes the input voltage to the
LM339 5.0 volts (12 VDC supply, 7mA through a 1 kohm resistor, Ohm's law
(V=IR), 7 volt drop from 12 volts gives you 5 volts). The trip
threshold of the LM339 is hard-wired to 5 volts, also. The LM339
circuit has no hysteresis, and there's a bunch of noise from the rest of
the machine. So the LM339 output (what's being polled by the CPU) is
sending (SWAG) dozens of pulses per second to the CPU, which then tries
to flip the upper left flipper dozens of time per second. Which
(mechanically) it can't do.
That explains all the symptoms I listed earlier. Buzzing. Weak
flipping. Sometimes no flipping. It's all a problem if current going
through the opto is around 7mA. Which it can be. And a light touch on
the flipper button results in less current through the opto, which
causes the same symptoms even with łhigher-current˛ optos.
So what's the fix? (WARNING: I TAKE NO RESPONSIBILITY IF YOU ATTEMPT
ANY OF THESE FIXES) A simple hack is to short out the 1N4004 diode on
the Fliptronic-II board. Sometimes this drops the input voltage to the
LM339 enough so that the comparator isn't trashed by other circuit
noise. But the fix that I put in was to replace the 1 kohm resistor
with a 2 kohm resistor. That results in doubling the IR drop across the
resistor, even with the same opto current, which drives the input of the
LM339 way past the comparator threshold voltage. I've had no problems
with my upper left flipper since putting this fix in. But remember,
there are no guarantees here, only warnings. Be careful...
I also thought that the (electrical) pounding the flipper coils took
might have weakened them so much that I'd have to replace them, but łso
far, so good˛ with no coil replacements.
===========================================
Problem: Upper *right* flipper was also weak sometimes
A blast of łDust Off˛ fixed this. This probably allowed more
illumination on the opto receiver, resulting in just enough current
through the opto to drive the input of the LM339 past the comparator
threshold voltage.
Again, a better (but harder to do) fix is to replace the dropping
resistor on the Fliptronic-II board.
===========================================
Problem: The ł0 minutes˛ opto on the clock was noisy, and would register
switch closures when the minute hand wasn't near it.
In test mode, when the clock motor was running, the ł0 minutes˛ opto on
the clock would register random switch closures. When the clock motor
wasn't running, the ł0 minutes˛ opto was perfectly well-behaved. But
that meant that the clock would fail the power-up tests...
Again, this was a problem with optos that just don't pass quite enough
current when illuminated. In this case, we had new clock boards from
PBLiz, and the LM339 comparator is on the main WPC CPU board. But the
explanation is the same as the (long-winded) one above.
And the fix was the same, too. Find the dropping resistor for the
mis-behaving opto. Replace it with a larger resistor (resistance-wise,
that is <grin> ). This results in a larger IR drop across the resistor,
even with the same opto current, which drives the input of the LM339 way
past the comparator threshold voltage.
It's interesting (at least to me) that this same problem showed up on
new clock boards from PBLiz. That says to me that the current-passing
capabilities of the optos being put in boards today are still varied
enough to give lots of TZ owners problems...
And there's not a lot we can do on the opto end of the circuit. The
problems are 1) not a big enough dropping resistor between the 12 VDC
supply and the LM339 input, and 2) no hysteresis in the LM339 circuit.
===========================================
Problem: Sometimes (a lot of times) the machine would say it was a
powerball, when it wasn't a powerball.
The proximity sensor in the trough had been knocked out of alignment.
This is a well-documented problem, with well-documented fixes that I
won't repeat here :-)
===========================================
Problem: Random machine resets.
This was a problem only a few times, for only a few hours on one day.
I'm hoping it was glitchy line power from Dominion Electric :-)
===========================================
Problem: The plastic piece above the top left flipper is cracked.
WTB: TZ plastic that goes above the top left flipper. It's the one with
the red background, showing a quarter-on-edge, a penny, and a couple of
gumballs.
===========================================
Problem: The ramp diverter/cage sometimes wouldn't dump the ball down
onto the playfield.
The ball would go into the cage, then it would just sit there. I could
hear the solenoid humming, but the cage wouldn't flip over. The machine
would go into ball-search mode, and pop everything, but it would take
many cycles of this until the ball would dump out of the cage.
The fix was to tighten the habitrail going to the upper playfield down
to the lower playfield. When the habitrail was loose, it made the
diverter/cage high enough that the solenoid could not drive the plunger
to flip the cage.
===========================================
Problem: Burned-out lightbulbs.
You can snitch replacements for (many of) the plug-in bulbs under the
playfield out of the GI lights in the backbox.
===========================================
Problem: The right jet bumper is a little sticky.
During the solenoid test, the right jet bumper would (temporarily) hang
up on the rubber bumper next to it. This was never a problem during
actual game play, so I haven't done anything about it.
===========================================
Problem: Right ramp needs to be screwed down (both sides).
We crammed toothpicks into the stripped holes, and that has held up
pretty well. I've heard that bamboo BBQ skewers work even better.
===========================================
Problem: Ball gets stuck on soft Hitchhiker shots.
A soft/weak shot up the Hitchhiker would result in a stuck ball (and
require a tilt to get the ball back).
The problem is the plastic to the lower left of the gumball machine (the
one that says łFresh - 1 cent - delicious˛). The lower tip of it was
hanging down into the Hitchhiker shot, and a soft shot would get stuck
between the plastic tip and the playfield. A little plastic bending
(using a hair-dryer) fixed this problem.
===========================================
Problem: Ball bounces out of the diverter/cage back onto the habitrail,
then the solenoid plunges before the ball rolls back into cage.
I know there's a magnet mod kit for this, but my fix was just a tiny
piece of double-stick foam covered with black electrical tape, stuck to
the inside of the cage when the ball hit. It works great - balls come
into the diverter/cage and just stop dead in there.
===========================================
Problem: Auto-kicker doesn't send the ball around the spiral reliably.
I'm still working on this problem. When the left-right leveling of the
playfield is just right (or wrong), balls shot into play by the
auto-kicker seem to bounce from side to side on their way around the
spiral. I think the most severe problem is if the ball hits the metal
corner of the łLock˛ kick-out. That seems to stop the ball in its
tracks, then it drops down past the upper right flipper. I'm still
trying to figure out how to have the auto-kicker send the balls around
the spiral reliably...
Padding on the *inside* wall of the right spiral seems to help a little
(cuts down on the side-to-side bouncing)
===========================================
Problem: Massive pop from the speakers when powering up and powering
down.
Got the WMS No-Pop Noise Eliminator Boards from Herb Schanke. Problem
solved.
===========================================
Problem: Didn't have the latest and greatest ROMs.
Got the version 9.4H ROMs from Action Pinball.
===========================================
That's it for now. Thanks for putting up with my long explanations, and
thanks to everyone else for their repair tips, too!
- Tim Kuo
Ed Faerman
flipper opto ciruit. Mine has been working fine, but I will keep your
experience in mind.
Ed
Rob G
dust off the optos. Almost all surfaces will retain a thin layer of
dust that cannot be removed by air itself. You really need to
use a q-tip to clean them properly.
--
Rob
"sinkva" <sin...@earthlink.net> wrote in message
news:sinkva-50B914....@news06.east.earthlink.net...
sinkva
"Rob G" <lost.in....@sasktel.net> wrote:
> Compressed air by itself probably isn't enough to clean the
> dust off the optos. Almost all surfaces will retain a thin layer of
> dust that cannot be removed by air itself. You really need to
> use a q-tip to clean them properly.
I did try cleaning the flipper optos with a Q-tip and Windex.
(after blasting them with air)
But there was little (no) improvement to my
what-at-the-time-was-a-problem upper left flipper.
Cleaning the optos (whether using compressed air or a Q-tip)
was only a partial fix.
The real fix was to replace (increase the resistance of)
the resistor between the 12 VDC supply and
the input to the LM339...
- Tim
Rob G
works fine need to be changed to work in your case? Is it more likely
that your fix is only curing the symptom of a problem that still remains?
The upper right flipper on my Whitewater was not working very well
and that was because the flipper opto board had a miniscule gap between
itself and the cabinet wall. The result was that the interrupter was just
barely allowing the opto switch to open , resulting in erratic switch
readings
and of course erratic flipper operation. I remounted the opto and the
problem
was solved. It's always a good idea to see how the flipper optos are
reading
in switch test mode. If they are fluctuating during normal use, that can
cause the coils to seem weak and overheat for example
--
Rob
"sinkva" <sin...@earthlink.net> wrote in message
news:sinkva-F4B1D5....@news06.east.earthlink.net...
Gruggy Poosh
<lost.in....@sasktel.net> wrote:
> I'm no electronics expert, but why should a design that normally
>works fine need to be changed to work in your case? Is it more likely
>that your fix is only curing the symptom of a problem that still remains?
I completely agree. The Fliptronic system is, IMO, really well
designed, and I've never needed to do any electronic mods to achieve
oustanding flipper action.
First thing to do is make sure the mechs are moving freely with no
binding. Most games found in their "natural" state could really use a
complete flipper rebuild at this point. Coils are usually fine, but
the cranks, links, plungers, coil stops, and sleeves all wear out with
use. Often someone has lubed the mechs and the lube has dried into a
sticky mess, making things worse. Just cleaning all of the parts can
do wonders.
If flippers are still weak, replacing the button optos with new ones
may be in order. It's pretty rare, but they do fail.
The ONLY other electronic repair I've ever had to do on a Fliptronic
game is to replace shorted drive transistors. I can imagine an LM339
going bad, but I haven't seen it happen on this particular board.
I'm not enough of an electronics whiz to really understand what
shorting out that diode does, but my instinct tells me it's a bad
idea.
--- Gruggy ---
Steven
I appreciate your long winded notes on optos, but you totally
missed the marked. Here's what you should have done: Buy a
damn new opto! The circuit doesn't need to be redesigned, you
just need a new clean opto. They are $5, and 5 minutes to install.
Fix the problem, don't band-aide it by redesigning the circuit.
The opto is wasted. Are you going to keep increasing the resistor
value as the opto gets worse and worse? Why not just put a big
honkin' pot in there so you can dial it up as the opto get worse?
Sincerely,
Steven R.
sinkva
pin...@yahoo.com (Steven) wrote:
> I appreciate your long winded notes on optos, but you totally
> missed the marked. Here's what you should have done: Buy a
> damn new opto!
No, IMHO you are missing my point.
The basic design of the LM339 comparator circuit
was fine for electro-mechanical switches,
but (when mated with optos the way WMS did it)
is a weak design, and
should 1) have had hysteresis built in, and
2) some more thought should have gone into what the
range of opto currents was.
And I saw the symptoms of these problems
in two totally different area of the machine:
1) weak flippers, and
2) noisy/erratic clock behavior
> The circuit doesn't need to be redesigned, you
> just need a new clean opto.
No, I cleaned the optos.
Air-blasted and cleaned with Q-tip&Windex.
It helped, but *DID NOT* fix the problem.
Just buying new optos would not necessarily solve the problem, either.
One of the optos was (I think) original, vanilla, stock
(the one on the opto flipper board),
but the other was on a brand new PBLiz clock board.
So buying a new opto would just be throwing the dice again.
> They are $5, and 5 minutes to install.
Resistors cost pennies each, and are easier to install than optos.
> Fix the problem, don't band-aide it by redesigning the circuit.
Agreed, but the correct fix is to fix the circuit.
And just replacing the resistor isn't a total fix.
I didn't even try to add hysteresis to the LM339 comparator circuit.
> The opto is wasted.
Why?
I'm using the exact same opto I started with.
I just replaced a resistor.
And (the acid test) I've had no more problems.
My 2 cents :-)
- Tim
sinkva
"Rob G" <lost.in....@sasktel.net> wrote:
> I'm no electronics expert, but why should a design that normally
> works fine need to be changed to work in your case?
That's the whole point here.
The circuit normally does work fine.
But only "normally".
In my case, I had totally different problems that
(in the end) were due to the opto current not being
in the "design that normally works" range.
And these optos came from totally different places,
so I have to believe that there are a lot more
optos like these that are not in the
"design that normally works" range.
One opto is (I think) the original.
The other opto was on a brand-new PBLiz clock board.
> Is it more likely
> that your fix is only curing the symptom of a problem that still remains?
I really doubt it.
I cleaned the optos first.
Air blasted, then Q-tip & Windex
The problem did not go away.
Then I measured a few
voltages around the optos and the LM339s.
And tried replacing the resistor.
The circuit behavior changed the exact way
I expected, and I have had no trouble since then.
No problems with either the weak flipper or with the
"noisy" clock opto. That (to me) is the acid test.
> The upper right flipper on my Whitewater was not working very well
> and that was because the flipper opto board had a miniscule gap between
> itself and the cabinet wall. The result was that the interrupter was just
> barely allowing the opto switch to open , resulting in erratic switch
> readings
> and of course erratic flipper operation. I remounted the opto and the
> problem
> was solved. It's always a good idea to see how the flipper optos are
> reading
> in switch test mode. If they are fluctuating during normal use, that can
> cause the coils to seem weak and overheat for example
We tried all of the obvious things like that,
even before cleaning the optos.
But a good hysteresis design in the LM339 comparator circuit
would have prevented your problem, too :-)
- Tim
sinkva
Gruggy Poosh <grugg...@bellsouth.net> wrote:
> I completely agree. The Fliptronic system is, IMO, really well
> designed, and I've never needed to do any electronic mods to achieve
> oustanding flipper action.
The Fliptronic system is well designed for sensing
classic electro-mechanical switches.
It is (at best) a weak design for sensing optos.
At least the way WMS mated their opto circuits with
the comparators on the Fliptronic-II board.
It's also a weak design for sensing optos
the way WMS mated their opto circuits with
the comparators on the CPU board.
It's a design that only works "most of the time".
Think about that.
I had a functional failure rate of over 11%.
For 2 out of the 18 optos on my Twilight Zone machine,
the design was flawed. I'm sure it has to do with
the normal range of expected opto currents,
but someone didn't do a good enough analysis there.
> First thing to do is make sure the mechs are moving freely with no
> binding. Most games found in their "natural" state could really use a
> complete flipper rebuild at this point. Coils are usually fine, but
> the cranks, links, plungers, coil stops, and sleeves all wear out with
> use. Often someone has lubed the mechs and the lube has dried into a
> sticky mess, making things worse. Just cleaning all of the parts can
> do wonders.
We tried all of those things.
I guess I should have made that clearer in my original post.
> If flippers are still weak, replacing the button optos with new ones
> may be in order. It's pretty rare, but they do fail.
IMHO, those optos aren't failing.
They are probably optos just within the
"works most of the time" range.
Then something changes. Lower wall power/rolling brownouts.
Dust build-up on the IR transmitter or receiver.
Whatever.
A replacement opto seems to work because it happens to be
more within the "works most of the time" range.
And everyone says, "We fixed the burned out opto!"
But it's really just another roll of the dice.
And a symptom of a weak circuit design.
My 2 cents.
> I'm not enough of an electronics whiz to really understand what
> shorting out that diode does, but my instinct tells me it's a bad
> idea.
I agree. And I think I said shorting out the diode was a hack...
- Tim
Rob G
Ok, what's a hystewhatchamacallit? :)
--
Rob
"sinkva" <sin...@earthlink.net> wrote in message
news:sinkva-BEDCDF....@news06.east.earthlink.net...
Gruggy Poosh
>It's a design that only works "most of the time".
>Think about that.
>I had a functional failure rate of over 11%.
I've worked on a ton of Fliptronic pins, and in my experience the
functional failure rate of the flipper switch-sensing circuit is
exactly zero percent. Maybe I've just been lucky.
Doowutchyalike with your game, but I think replacing the opto is a
better fix than hacking the Fliptronic board. The opto will eventually
die altogether anyway.
If you want to re-evaluate a solid-state flipper board that has design
flaws, try the old Data East board. I've seen a few of those where
some mysterious problem took out a bunch of transistors, domino-style.
This is one area where Williams was clearly the best.
Oh, wait.... I've never had any problems with Gottlieb's solid-state
flippers, either. ;-)
--- Gruggy ---
Fred Kemper
boards to the Liz Schmitt-trigger style
replacements.
Proxy sensor replacement:
http://www.pbliz.com/id128.htm
(Solves the "check switch 26" problem.)
Sounds like you still have other problems
that you have now masked as well, IMO
--
Fred
TX
CARGPB#8
******************
"sinkva" <sin...@earthlink.net> wrote in message news:sinkva-50B914....@news06.east.earthlink.net...
<SNIPPED>
sinkva
"Fred Kemper" <pbga...@davlin.net> wrote:
> OR, you could just change the flipper opto
> boards to the Liz Schmitt-trigger style
> replacements.
>
> http://www.pbliz.com/id33.htm
Hmm. Very interesting.
It's not clear whether the PBLiz "Type 2 Flipper Opto Board"
is appropriate for Twilight Zone machines.
Their website seems to imply that it's not.
Can anyone give an informed "yes" or no" ??
Maybe WMS (or PBLiz) alreadydid a
pre-packaged solution for the
(original, TZ-timeframe) weak flipper opto design :-)
> Sounds like you still have other problems
> that you have now masked as well, IMO
I'd love to add some hysteresis into the LM339
comparator circuit, but my machine plays
(and tests) fine now, so I'm going to leave
well enough alone...
- Tim
sinkva
"Rob G" <lost.in....@sasktel.net> wrote:
> Ok, what's a hystewhatchamacallit? :)
Hysteresis.
From the Internet:
"a retardation of an effect when the forces acting upon a body are
changed (as if from viscosity or internal friction); especially : a
lagging in the values of resulting magnetization in a magnetic material
(as iron) due to a changing magnetizing force"
For normal people, it's when the switching from off-to-on happens
at a (slightly) different threshold than the switching from
on-to-off.
A good real-world example is your thermostat.
Say it's set for air-conditioning at 72 degrees.
Your air conditioner probably doesn't click on
until the house temp is 73 degrees.
And the thermostat doesn't turn off
until the house temp is 71 degrees.
Why? That keeps the air conditioner
from switching on and off from every little air current
as people walk past the thermostat.
That (hysteresis) behavior is not built into the
LM339 comparator circuits in the TZ Fliptronics board,
nor in the TZ CPU board.
So small variations in voltage can cause the
output of the LM339 to go
high-low-high-low-high-low-high-low-high-low-high-low...
Those small variations can (and almost certainly do)
come from the 5 VDC supply,
the 12 VDC supply, the opto circuit, etc.
You can see it in your own TZ machine.
Gently and slowly press a flipper button in.
At some point (probably) on one of the flippers
(left/right, upper/lower), you'll start to see the
flipper oscillate up and down. Or it may flip
halfway out. Or it may just buzz.
Pressing the button all the way in should
make the flipper go out (flip) strongly all the way.
This behavior is because the output voltage of the opto
varies continuously over its range.
It's not like the classic electro-mechanical switch,
where the switch was truly either "open" or "closed".
If the LM339 comparators had hysteresis, then once they flipped,
they would stay flipped until (say) the button was released
all the way. That would keep the flippers from oscillating.
And would make the LM339 circuit much less sensitive to
variations in opto current.
- Tim
sinkva
Gruggy Poosh <grugg...@bellsouth.net> wrote:
> I've worked on a ton of Fliptronic pins, and in my experience the
> functional failure rate of the flipper switch-sensing circuit is
> exactly zero percent. Maybe I've just been lucky.
You've never replaced an opto on a flipper board?
I'll bet that opto hadn't failed.
I'll bet that something else changed to make that whole
opto/LM339 circuit combination stop working.
Like lower wall power/rolling brownouts, or
dust on the opto, or noisier 5 VDC or 12 VDC power.
And that's a functional failure.
Replacing the opto might have resulted in swapping in
an opto that was more "in spec", so the circuit started
working again.
But - overall - that's still a functional failure...
> Doowutchyalike with your game, but I think replacing the opto is a
> better fix than hacking the Fliptronic board. The opto will eventually
> die altogether anyway.
Why? What causes the optos to die?
If this is one of those things where the fix is:
"Just keep swapping optos until the circuit works again",
then my theory makes just as much sense as
"all optos weaken and eventually die".
Right?
My 2 cents, of course.
- Tim
Fred Kemper
board as well.
The Type 2 board will work, (with a little rewiring), but
you will need to come up with a plastic interrupter to complete the
changeover. This cures the 'half-assed' opto closure problem.
--
Fred
TX
CARGPB#8
******************
"sinkva" <sin...@earthlink.net> wrote in message news:sinkva-191FA9....@news06.east.earthlink.net...
Rob G
transmitters that looked darker than normal and needed replacing.
--
Rob
"sinkva" <sin...@earthlink.net> wrote in message
news:sinkva-5516B8....@news06.east.earthlink.net...
Gruggy Poosh
>You've never replaced an opto on a flipper board?
Like I said before, I have replaced an opto -- but I was counting that
as the switch, and not part of the switch-sensing circuit.
But actually, I can only remember having to replace a flipper opto
once.
>I'll bet that opto hadn't failed.
>I'll bet that something else changed to make that whole
>opto/LM339 circuit combination stop working.
Uh, I don't think so. In the one case where I had to replace the
flipper board opto, that opto was totally dead -- not just slightly
out of specl. Swapping another one in made it work like new again.
>Why? What causes the optos to die?
I don't know. But it does happen. Old LEDs can get dimmer.
Phototransistors can just stop working. Birds can stop singing.
In the case of the flipper optos, it's kind of hard to tell which half
of the opto has failed, since they're mounted inside that plastic
housing. But with the separate optos used in other parts of late-model
pingames, it's much easier. Dim LEDs on trough boards are really easy
to spot with an infared detector, since you've got several others
right there to look at for comparison.
>If this is one of those things where the fix is:
>"Just keep swapping optos until the circuit works again",
>then my theory makes just as much sense as
>"all optos weaken and eventually die".
I didn't say to "keep swapping optos until the circuit works again". I
said to replace the failing opto with a new one, and the problem will
go away.
--- Gruggy ---
Gruggy Poosh
>You can see it in your own TZ machine.
>Gently and slowly press a flipper button in.
>At some point (probably) on one of the flippers
>(left/right, upper/lower), you'll start to see the
>flipper oscillate up and down. Or it may flip
>halfway out. Or it may just buzz.
>Pressing the button all the way in should
>make the flipper go out (flip) strongly all the way.
>This behavior is because the output voltage of the opto
>varies continuously over its range.
>It's not like the classic electro-mechanical switch,
>where the switch was truly either "open" or "closed".
I just went and tried this on my TZ. If the flipper button is held in
just right, the GI dims and a buzzing sound can be heard. As you
describe, it's as if the "switch" is rapidly pulsing on and off.
After approximately two seconds of keeping the opto receiver in this
shadowy middle ground between light and darkness, the buzzing stops
and the GI returns to normal. It appears that the CPU has spotted this
indecision, decided it needs to stop, and switched the flipper to
"hold" mode.
And yes, I'm sure my fingers didn't slip and push the button in a
little bit farther.
>If the LM339 comparators had hysteresis, then once they flipped,
>they would stay flipped until (say) the button was released
>all the way. That would keep the flippers from oscillating.
>And would make the LM339 circuit much less sensitive to
>variations in opto current.
You know, I always thought Fliptronic flippers gave an incredible
degree of control to the player. It seemed intangible, but when it
came to doing finesse tricks like live catches or post passes -- which
require extremely soft, quick taps of the flipper buttons -- I just
could never do them as easily on DE's solid-state flipper games. DE's
flippers seem to have an "on or off" quality that's very much like the
"hysteresis" that you describe.
I think you may have finally explained this for me. Thanks!
--- Gruggy ---