Gottlieb logo Installing Pop Bumper Drivers
on a System-1 Machine
Gottlieb logo

I finally had enough of the whimpy pop bumpers on my Joker Poker System-1 machine and after several attempts to adjust them trying to improve their performance, I gave up and decided to install a pair of System-80 Pop Bumper Driver Boards (PBDB) hoping to liven things up a bit.

Figure 1
Gottlieb System-80 Pop Bumper Driver Board

Original System-1 pop bumpers were designed to work all by themselves without any intervention from the MPU, other then registering a score or making a noise. They look like normal pop bumpers found on Bally machines (which ARE computer controlled) as far as the parts go, but operate in a completely different manner.

On System-1 machines, when the ball hits the skirt on the pop bumper, the skirt closes a switch. This switch then supplies +35VDC to the pop bumper's coil. The other lug of the coil is already connected to ground, so the coil is now energized and it pulls the ring down, thus "popping" the ball. The ball then rolls off of the skirt, the switch then opens up removing the power to the coil, the coil relaxes, and the ring pulls back up thanks to a spring on the coil's plunger.

So you can see that the duration of the pop, which has a lot to do with the strength of the pop, is completely related to the length time the ball is on the skirt. Usually, this works fine, but sometimes it just does not make contact with the skirt long enough to allow the coil to pull the plunger completely in, which is required for a good strong pop. Bally on the other hand has the skirt switch connected to the MPU, and when the switch closes, even for a moment, it sends a signal to the solenoid driver to fire the coil using a fixed pulse. Because the pulse delivered to the coil from the solenoid driver has a fixed duration, you always get a nice, strong, and consistant pop. That's why you don't see many whimpy pops on the Bally machines - the duration of the pop is controlled by the MPU, NOT by a spoon-switch. The picture below illustrates the circuit for a normal Gottlieb System-1 Pop Bumper.

Figure 2
Gottlieb System-1 Pop Bumper Circuit

Gottlieb fixed this on their System-80 machines by introducing the Pop Bumper Driver Board. The PBDB adds additional circuitry to the pop bumper circuit which in controls the pop in a way that's similar to the Bally solenoid driver. Now when the ball hits the skirt on the pop bumper, the skirt still closes a switch, but this switch goes to the PBDB instead of the pop bumper's coil. When the switch closes, even if it's a very short closure, a signal is sent to the PBDB. This signal causes the circuitry on the PBDB do deliver a nice uniform, and consistant pulse to a power transistor on the board. This transistor acts like a switch and will apply power to the pop bumper's coil as long as the transistor is turned on (i.e., for the length of the pulse). So now the pop bumper's coil is energized in a nice uniform, and consistant manner, thanks to the PBDB! The picture below illustrates how the pop bumper driver board is connected to the pop bumper (each pop bumper has it's own PBDB). The diagram of the PBDB is not accurate as far as the pin placement goes, I rearranged them to make the drawing easier to understand, and the wire colors correspond to the connector I built:

Figure 3
Gottlieb System-1 Pop Bumper w/ a PBDB (Notice there are 2 wires connected to Pin 6)

Figure 2 and 3 are really all you need to know in order to apply this mod to your machine. If you want to learn more on how I did it, then read on (the hardest part was running the wires to supply the 5VDC from the MPU to the underside of the playfield):

In the Figure 3 above, you'll notice things are wired a little differently. With the PBDB, each pop bumper coil is connected to the +35VDC bus. This connection is made on the coil's lug that's connected to the banded side of the coil's diode. The job of the PBDB is to connect the other lug of the coil to ground, which will then complete the coil's circuit and energize the coil (just like on a Bally!). What makes this work so well is how the PBDB makes this connection in a uniform, and consistant amount of time, no matter how long the spoon switch is closed. As a bonus, if the spoon switch should become stuck in the closed position (via a mis-aligned skirt, etc.), the pop bumper will still only receive a single pop. This is because the PBDB must sense the spoon-switch opening, before it will energize the coil again. Nice! On original System-1 machines, should the skirt become jammed such that the spoon-switch was always closed, the coil would remain energized and would fry.

You'll also notice a 2nd switch on your Gottlieb System-1 (and System-80) pop bumpers, which is not involved in the firing of the coil at all. This 2nd switch is activated by the pop bumper's yoke and is used to tell the MPU a pop just occured, so it can make a noise, score points, etc. Again, this is because the pop bumpers are not MPU controlled, so it need's this switch so the MPU can tell when the pop bumper has popped. Below is a picture showing both the spoon switch and the score switch:

Figure 4
System-1 pop bumper switches

OK, so now that you know the basics. Here's how I installed PBDBs on my System-1 Joker Poker, which basically involves rewiring things so they look like the Figure 3 above. (click on any picture to see a bigger one):

First thing that's needed is a 5VDC power source. Unfortunately, there's none available on the playfield, at least not on my Joker Poker. So I had to 'borrow' 5VDC from the power supply board. Since there's a wiring harness from the MPU board that goes to the top of the playfield (J7) which just happens to be next to the connector from the power supply (J1). I tapped the power off the J1 connector (pin 2 for positive and pin 3 for negative) on the MPU and attached a 2-conductor Molex connector so I can easily disconnect it if I have to. I did this by removing the two connectors from the J1 housing, cutting them off, then crimped on new connectors that were made for bigger wire gauges in order to better accomodate 2 wires.

Next, I installed the mating 2-conductior Molex connector on a pair of 20 AWG black and red wires long enough to reach all the way to the playfield, and then some. I threaded these wires into the harness to help keep it nice and neat.

Note that my J7 harness had some issues when I first got this machine and I had to splice in a new J-7 connector, so it starts out with nylon wire ties where I did the work, but then later on down the line was the the original wire-wrap. I used a small phillips screwdriver and inserted it under each wrap to open it up a bit, then quickly removed it and inserted the ends of the two wires, then pulled them through. I continued all the way to the end of the harness.

Click on either to see a bigger picture

With the playfield up, I then mounted a terminal strip on the bottom of the playfield near the wire harness w/ my two wires, and attached the red and black wires to it. I will then use these two terminals later as a source for 5VDC, which is required by the pop bumper driver boards.

Click to see a bigger picture

Next, I mounted the two PBDB near the two pop bumpers on my Joker Poker. I used tall spacers so I could mount them over wires and such. I also made damn sure the screws I used were not long enough to pop through the top surface of the playfield. Be careful when you mount them that they are not in the way of anything when you lower the playfield back down into the cabinet. When I first mounted the one on the right, I had it too close to the side and it hit the playfield guide rails.

Click either to see a bigger picture

I also built connectors for the two boards. I used 6-conductor Molex 0.156" housings with a key in pin 4. I also used trifurcon pins, but not for their current handling capacity, but because they grip the pins better. I figured since the boards will be upside down, the extra gripping would come in handy. The housing also has a locking ramp for added safety. I used different colored wires to make it easy to install the connector, and also used two long lengths of 20AWG black and red wire to connect to the 5VDC source I added. Notice how pin six has two wires connected to it - both black. One is for the -5VDC and the other is to supply a ground connection to the spoon-switch.

Pin 1: Orange, this gets connected the coil on the side of the diode opposite the banded end
Pin 2: Brown, this gets connected to the black ground bus wires that were originally on the pop bumper coil
Pin 3: Green, connected to the spoon switch
Pin 4: Key (not used)
Pin 5: Red, to the +5VDC supply
Pin 6: 2x Black, one to the 5V supply, one to the other spoon switch

Click either to see a bigger picture

Now it's time to remove some wires from the pop bumper and the spoon switch. The pictures below show which wires need to be removed from the pop bumper coil and the spoon switch. Basically remove them all, you want all wires removed from the spoon switch and the pop bumper coil. Toss the little wire that goes from the spoon switch to the coil, and keep track of the pair of black wires and the three brown wires. Note that these colors are from my Joker Poker and I don't know if your System-1 machine is the same, but the wiring *should* be similar. Also, be careful to remove the wires from the coil as quickly as possible so you don't fry the diode with the heat from your soldering equipment.

The picture on the left is before I did anything, and the picture on the right is after I removed all the wires. It's hard to see both lugs on the spoon switch, but I removed the wires on both of them, plus the wires on both lugs of the coil. On the spoon switch, there was one group of 3 wires on one lug - this is the +35VDC bus. On my machine these wires are brown w/ a black tracer (they may be different on yours). The other spoon switch lug had a small wire that went to the coil lug attached to the banded side of the diode. This small wire can be discarded. The other coil lug had two black wires on it. These are the ground bus wires.

And remember - Don't confuse the score swich w/ the spoon switch. The spoon switch is the one on the stack that's closest to the underside of the playfield, and has the spoon-looking thing on it.

Click either to see a bigger picture

So now in the picture above on the right (the 'after' picture), you can see there are only two wires left, the pair of black ground bus wires, and the set of brown +35VDC bus wires. You can also see the two empty coil lugs and maybe the two empty spoon switch lugs. These all will be used in the next step.

Now it's time to hook the PBDB up to the pop bumper, using the connector I built earlier. I plugged the connector into the board's header pins, then neatly routed the orange wire off pin 1 to the coil lug with the unbanded side of the diode. I cut the wire to length and soldered it onto the lug. Next, I took the brown wire off pin 2, routed it neatly, and soldered it to the pair of black ground bus wires that I removed from the coil earlier. I used heat shrink to make it neat but don't forget to put the tubing on BEFORE you solder the wires!. Finally, I took a small piece of wire and, using heat shrink tubing again, connected the 3 brown +35VDC bus wires to the other coil lug, the one with the banded side of the diode connected to it. I figured it would be easier to connect a single wire to the coil, instead of trying to connect all 3 brown wires, plus I don't think they would have reached anyway.

Click any one to see a bigger picture

Almost Done! Now I connect the short black wire off the connector to one lug of the spoon switch, and the green wire off the connector to the other lug on the spoon switch. It does not matter which wire goes to which lug. Again, I routed the wires as neatly as I could from the PBDB to the switch, leaving a little slack so I could remove the connector if I had to.

Then I ran the long pair of red and black wires to the terminal strip I installed earlier. These wired got connected to the red and black wires that go to the power supply.

Click either to see a bigger picture

All done! Here's how they both look after I finished:

Click either to see a bigger picture

After I installed everything, I dressed up the spoon switch contacts w/ a flex-stone and adjusted the gaps. After playing a few games, I came to the following conclusions:

Good Stuff:

Bad Stuff:

Overall, I'm very pleased with the way this mod turned out.

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Created 6/20/06 - Last Modified 6/28/06 - Steve Kulpa   Mail Icon Nolensville, TN
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