EM Question Regarding Late Model Gottliebs - Diodes, Resistors, and Caps
Gott Lieb?
relays along with electrolytic caps across the lugs? Also, why were
diodes used across the lugs of the PF coils that were supplied with DC
voltage from the bridge rectifier? Was this to isolate back fed current
so other coils wouldn't fire or pulse?
Jim
CARGPB35
kirb
I assume you are talking about EM GTB games as the subject states.
What games are you talking about?
Some resistors were used so that 6 volt systems could be used in the
24 volt side. Some caps were used as time delays in early games. Caps
could be used on games with DC to snub an arc across a DC contact. DC
contacts take more of a beating because there is no zero crossing of
the waveform and more arcing happens. I've seen resistors used with DC
caps as snubbers, but never on a pinball.
Diodes, as in SS games, are used as a flyback diode to kill the energy
stored in the coil. This helps save EM contacts like it helped save
transistors.
Kirb
Gott Lieb?
In this case, it's a Joker Poker. I assume the crossover games
starting with Cleo and ending with Space Walk have similar items added
to their circuits.
There are two resistors on two separate lamps, which are on the solenoid
bus. I figured these resistors were used to step the voltage down. I
just was not certain why there were resistors in series with the diodes
on some relays that had caps. Even one relay has a resistor, but no
diodes. This particular relay uses a common A-9736 coils.
Here's a link to a pic, which has a portion of the schematic with two of
these circuits - http://www.jtamusements.com/im000187.jpg. Look towards
the top at the Game Over (Q) and 1st Ball (U) relay circuits. Both of
these relays are the "newer", high impedance A-16890 coils.
Jim
CARGPB35
TimMe
> Thanks for the info, Kirb. Yes, these pieces are all on a Gottlieb EM.
> In this case, it's a Joker Poker. I assume the crossover games
> starting with Cleo and ending with Space Walk have similar items added
> to their circuits.
>
> There are two resistors on two separate lamps, which are on the solenoid
> bus. I figured these resistors were used to step the voltage down. I
> just was not certain why there were resistors in series with the diodes
> on some relays that had caps. Even one relay has a resistor, but no
> diodes. This particular relay uses a common A-9736 coils.
>
> Here's a link to a pic, which has a portion of the schematic with two of
> the top at the Game Over (Q) and 1st Ball (U) relay circuits. Both of
> these relays are the "newer", high impedance A-16890 coils.
>
> Jim
> CARGPB35
>
>
>
> kirb wrote:
> > I assume you are talking about EM GTB games as the subject states.
> > What games are you talking about?
>
> > Some resistors were used so that 6 volt systems could be used in the
> > 24 volt side. Some caps were used as time delays in early games. Caps
> > could be used on games with DC to snub an arc across a DC contact. DC
> > contacts take more of a beating because there is no zero crossing of
> > the waveform and more arcing happens. I've seen resistors used with DC
> > caps as snubbers, but never on a pinball.
>
> > Diodes, as in SS games, are used as a flyback diode to kill the energy
> > stored in the coil. This helps save EM contacts like it helped save
> > transistors.
>
>
> - Show quoted text -
These appear to be simple DC power supply circuits. The resistor
lowers the effective voltage that will be developed on the DC side of
the supply rail, and the cap is there as a filter cap (like on any
other DC power supply) to smooth out the extreme DC ripple that would
be present due to the single diode that is acting as a half-wave
rectifier -- I imagine the relay armature would buzz like an old
electric alarm clock without that cap. As Kirb says, the back-EMF
diode across the relay coil is there to prevent high reverse-voltage
spikes that could damage the rectifier diode.
As to WHY all this, here is my guess: This was at a time when
Gottlieb was reducing the fabricated parts count in their EM games for
cost cutting. They got very creative, and were able to completely
eliminate the control bank on some games. So instead of bank relays
that were set and tripped mechanically, they used AG-type relays that
just stayed pulled in to simulate set and trip behavior. This would
mean that some relays (like game over) would need to be able to stay
pulled in for very long periods of time. A high-impedance coil is
less prone to fry from continuous duty, but you need DC on this type
of coil to develop enough magnetic energy to pull in a relay armature
with a lot of contacts. The earlier, AC-driven hold coils probably
didn't have enough magnetic oomph to reliably pull in and hold a relay
with a lot of contacts, and reliable operation is kind of important
for a function like game over. Hence, the use of these DC coils and
their related satellite power supplies. As I said, just my guess.
- TimMe (CARGPB3)
c...@provide.net
control bank), a couple 3 relays become continuous
duty. That is, they are on all the time after the game
is over. This includes a Hold relay, Game over relay,
and First ball relay.
At first gottlieb put in 15 ohm relay coils for these
jobs. But within a couple years, the continuous on
relay coils would burn (ohms too low, consumes
too much power).
So instead they changed to a 220 ohm coil. But
they can't run on 30v AC with that high of ohms. Sure
they will never burn, but they will chatter and barely
pull in. To fix this, they use 2 diodes to effectively
1/2 wave rectify the AC power. This is enough
to keep the relay pulled in without chatter, and
since the resistance of the coil is so high, it will
never burn.
On Jan 13, 10:55 pm, Gott Lieb? <r...@papinball.com> wrote:
> Thanks for the info, Kirb. Yes, these pieces are all on a GottliebEM.
> In this case, it's a Joker Poker. I assume the crossover games
> starting with Cleo and ending with Space Walk have similar items added
> to their circuits.
>
> There are two resistors on two separate lamps, which are on the solenoid
> bus. I figured these resistors were used to step the voltage down. I
> just was not certain why there were resistors in series with the diodes
> on some relays that had caps. Even one relay has a resistor, but no
> diodes. This particular relay uses a common A-9736 coils.
>
> Here's a link to a pic, which has a portion of the schematic with two of
> these circuits -http://www.jtamusements.com/im000187.jpg. Look towards
> the top at the Game Over (Q) and 1st Ball (U) relay circuits. Both of
> these relays are the "newer", high impedance A-16890 coils.
>
> Jim
> CARGPB35
>
>
>
> kirb wrote:
> > I assume you are talking aboutEMGTB games as the subject states.
> > What games are you talking about?
>
> > Some resistors were used so that 6 volt systems could be used in the
> > 24 volt side. Some caps were used as time delays in early games. Caps
> > could be used on games with DC to snub an arc across a DC contact. DC
> > contacts take more of a beating because there is no zero crossing of
> > the waveform and more arcing happens. I've seen resistors used with DC
> > caps as snubbers, but never on a pinball.
>
> > Diodes, as in SS games, are used as a flyback diode to kill the energy
> > stored in the coil. This helps saveEMcontacts like it helped save
> > transistors.
>
> > Kirb
kirb
> On certain coils in the 1976 and later Gtb Ax/Bx era (no
> control bank), a couple 3 relays become continuous
> duty. That is, they are on all the time after the game
> is over. This includes a Hold relay, Game over relay,
> and First ball relay.
>
> At first gottlieb put in 15 ohm relay coils for these
> jobs. But within a couple years, the continuous on
> relay coils would burn (ohms too low, consumes
> too much power).
>
> So instead they changed to a 220 ohm coil. But
> they can't run on 30v AC with that high of ohms. Sure
> they will never burn, but they will chatter and barely
> pull in. To fix this, they use 2 diodes to effectively
> 1/2 wave rectify the AC power. This is enough
> to keep the relay pulled in without chatter, and
> since the resistance of the coil is so high, it will
> never burn.
After looking at the schematic, I have to agree with Clay. The always
powered relays were a problem in the late 70's games with burning and
buzzing. Converting it to a crude DC would help stop the buzz and the
high resistance would stop the burn.
I might do this conversion to a fire queen game that I can't get to
stop buzzing no matter what adjustments I do to the hold coil.
Kirb
Gott Lieb?
because Clay had mentioned this in a thread months ago. If I remember
right, the thread was regarding someone replacing a hold coil. My main
questions were about the caps and power resistors used on the relay
coils. I couldn't comprehend why they were put in place. Plus, a
question about the diodes across lugs if they were fed by the bridge rec.
Thanks for everyone's input. It all makes a little more sense now.
Jim
CARGPB35
kirb
> My main
> questions were about the caps and power resistors used on the relay
> coils.
The cap helps "smooth" out the half-wave DC to make it more like true
DC. I doubt there would be much need for it due to it being so small.
The power resistors are just there to drop the voltage to the coil.
Not sure why they didn't design the coil without the resistors, but
maybe that was a way to cut the coil burn.
> question about the diodes across lugs if they were fed by the bridge rec.
That answer is the same on SS and EM machines- it kills the built up
field still in the coil when you turn it off. The votlage can spike
quite high and cause contact burn. Putting a "flyback" diode across
the coil shorts this coil energy on to itself after the power is
removed greatly reducing contact arcing. This is also done on SS
machines to avoid too much back EMF on the transistors.
Kirb
TimMe
Actually I think in this case it's not the contacts that are the
concern, it's protection for the rectifier diode, just like (as you
say Kirb) it's used to protect transistors on SS games. A diode can
be destoyed by a large reverse-junction spike just like a transistor.
- TimMe (CARGPB3)
TimMe
> I couldn't comprehend why they were put in place. Plus, a
> question about the diodes across lugs if they were fed by the bridge rec.
Just for completeness, Jim, that isn't a bridge rectifier (which is
constructed from four diodes) it's just a single diode used to block
the negative-going half of the incoming AC cycle, hence the term "half-
wave rectifier." This is why you really need the filter cap to smooth
the DC, otherwise it would be extremely choppy and would not operate
the relay correctly.
Take care - TimMe (CARGPB3)
kirb
> Actually I think in this case it's not the contacts that are the
> concern, it's protection for the rectifier diode, just like (as you
> say Kirb) it's used to protect transistors on SS games. A diode can
> be destoyed by a large reverse-junction spike just like a transistor.
Yes, I agree.
Kirb
c...@provide.net
Actually that's not true.
You don't need the cap. I have done this
before, as a way to prevent burn on the
Game-Over relay (using a higher ohm coil).
I never use a cap. BUT i will say this. If you
do use a cap, the propensity for relay chatter
is decreased.
Gott Lieb?
circuits, feeding DC to some of the PF coils. It feeds the flippers,
pop bumpers, and single slingshot. Gottlieb started using bridge recs
with Cleo.
Jim
CARGPB35
TimMe
> Tim, there is actually a bridge rectifier, not related to the relay coil
> circuits, feeding DC to some of the PF coils. It feeds the flippers,
> pop bumpers, and single slingshot. Gottlieb started using bridge recs
> with Cleo.
Yep, sorry about that Jim, I mis-read your post. - TimMe
(CARGPB3)
TimMe
> You don't need the cap.
I'm sure you're right Clay, but I'm wondering if we are really talking
about the same circuit here. When you do this successfully, is the
game is on high-tap? Do you have the 6-ohm voltage dropping resistor
in the circuit? I'm thinking those might affect whether or not the
relay will work on unfiltered half-wave DC.
- TimMe (CARGPB3)
c...@provide.net
High Tap = yes.
Resistor = No.
Just the 2 diodes.
I have to do this on 1975 and later gottliebs
if i want to replace the burnt 30 ohm relay
(sorry i said it was 15 ohm in my post)
and not have it burn up again.
This is a Tim Arnold trick too. he has a
whole museum full of games where
that was done (no cap, no resistor, high tap).