(Topic ID: 258086)

Bally EM 00-90 Match Unit - Torn Down, Analyzed, and Demystified

By xsvtoys

3 months ago

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  • Latest reply 51 days ago by wayner
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match unit 2b.gif
00-90 unit right 4 (resized).jpg
00-90 unit right 3 (resized).jpg
00-90 unit left 1 (resized).jpg
9 right pcb installed 2 (resized).jpg
9 right pcb installed (resized).jpg
8 springs installed (resized).jpg
7 stop plate installed (resized).jpg
6 ratchet and drive pawl installed (resized).jpg
5 left PCB mounted (resized).jpg
2 ratchet rear wiper attached (resized).jpg
2 ratchet front wiper attached (resized).jpg
1 hold pawl installed (resized).jpg
18 ratchet removed (resized).jpg
coil sleeve shortened (resized).jpg
00-90 unit coil sleeve comparison (resized).jpg

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#1 3 months ago

Here you will find more than you probably ever wanted to know about one type of stepper unit, a Bally 00-90 Match Unit as found in a Bon Voyage pinball machine.

DISCLAIMER There isn’t anything really new as these stepping units or steppers as they are often called have been covered before fairly extensively. In particular Clay’s guides provide really solid information about how they work and how to repair them.

Even with the great information from Clay and other sources, I still felt a lack of understanding as to exactly how these things work, and also a bit of fear of working on them. When I looked at them I saw a complicated-looking contrivance with a bunch of levers and springs and gears with teeth. What if I got it apart and couldn’t get it back together so it would still work right? What if I put something on backwards and messed the whole thing up? What if I killed the function of the whole machine by messing with it? Even though the guides are detailed and excellent, there are still differences between the different stepper units, so you don’t get the specific details on one individual unit you have until you actually work on it.

Since I have 2 Bally EMs with a variety of these stepper units, some of which are definitely sluggish and some not even working 100% right, I knew I had to bite the bullet and just go after it and get it done. But I had to do it in my OCD fashion, figuring out every little piece as I went along. And that’s how you get what you have here. I found that once I got in there, took it all apart, figured out how it works, and cleaned everything up I was able top then easily reassemble it and get it to optimal working condition.

I hope to add some additional details and documentation about this specific stepper unit that others find useful. If you have a Bally EM with this style of 00-90 unit then most of this should directly apply as it appears they used very similar variations of these steppers in a lot of machines (from looking at the parts catalogs). I am not sure how much will apply to other brands as so far I only have Bally machines. But if anything this should provide some useful background information about how these work and how they are put together.

As always any comments, corrections, or criticisms are always appreciated.

#2 3 months ago

The 1974 Bally Bon Voyage is used for this guide. This machine uses a basic 00-90 match unit to control the match function. This is a different 00-90 match unit than is typically shown in the Bally parts catalogs which is this type:

Bally 00-90 Match Units (resized).jpg

As noted in the 1976 parts catalog the style of match unit found in the Bon Voyage was first used in Sky Kings, and subsequently used in the same basic form for Delta Queen, Rogo, Bon Voyage, Boomerang, Flicker, Air Aces, Knockout, Wizard, Bow and Arrow, Flip-Flop, and Hokus Pokus through Capt. Fantastic.

Interestingly this type of 00-90 Match Unit does not get its own drawing and description in the parts catalog. Instead, as noted on the Match Units page under Sky Kings it is the “same as Score Counter Unit” with various changes. So for a reference drawing and parts list we use the Snap-Out Score Counter Units from page 111 of the 1976 parts catalog.

Snap-Out Score Counter Unit (resized).jpg

So yes this unit is basically the same as the familiar score reel units. The major differences are that this unit does not have any switches and it has two circuit boards mounted to it instead of one. The parts highlighted in red in this picture are found in the score counter units but NOT in this 00-90 match unit.

Snap-Out Score Counter Unit as 00-90 (resized).jpg

Also note that even though all of the machines listed above use this style match unit there are various difference in the details for some of the machines. For example, some like Delta King, Air Aces and Hokus Pokus through Capt. Fantastic have a switch on this match unit that is most commonly used by the alternator relay. The pinball machines that are labeled as being the same as Bon Voyage are Wizard, Bow And Arrow, and Flip-Flop.

Another consideration when working on one of these is that it is also possible that everything is not exactly as it was originally. During 40+ years of service life various people may have had their hands on things, and possibly things are not assembled correctly, parts might be missing or substituted and so forth. So it should not be a surprise if another machine is slightly different. But I believe this particular match unit is accurate to its original state.

The history of this particular 00-90 match unit is unknown (to me). Why did Bally change the design of this match unit from the other style that had been used in many prior machines? My speculation is that it was decided to simplify the match unit for cost savings as this is a simpler version than the larger one with less moving parts. Also being based on the already-present score counter units it used existing engineering and parts.

This stepper unit is the type known as a Continuous Stepping Unit. That means it just goes around and around in one direction. Each time it gets a signal it advances one step. This is the simplest of the Bally stepper units. If you are just starting out and tackling the idea of working on pinball stepper units, this is a good type of stepper unit to start with because it has less complication and fewer parts than the other types such as Full Reset and Single Step Reset. This makes it less intimidating to work on.

#3 3 months ago

Here is the unit as mounted in the backbox of the Bon Voyage. Note that it is conveniently located and has lots of space around it which will make it easier to work on.

backbox inside (resized).jpg

A good test for any stepper unit is to locate the solenoid plunger that advances the unit and use your finger to push it in. It should feel free and make a crisp movement when it steps. If you feel a lot of resistance or if it seems to advance sluggishly then the unit may be dirty or gummed up, which will affect its function and is our incentive for taking it apart to service it.

You can also test this unit to see how it works with the match lights. With the game in game over mode (so you can see the match number lights in the backglass) you can press the solenoid plunger and cycle through the 10 numbers. They should proceed to light up in a consistent and orderly fashion. If there is strange behavior like missing numbers, skipped numbers, etc then this is a sign there is a problem. Of course be sure all 10 bulbs are good also. This Bon Voyage did have some erratic behavior with the match lights and that meant I had to jump in and sort it out, which expanded into this guide.

It would be great if unit could be taken out and set on a bench to be worked on. This could be done by unsoldering the wires connected to it but no way I’m doing that with 20-odd wires. You could also cut the wires and put in a connector that would allow the unit to be unplugged and taken out. That would be convenient but probably not worth the effort as realistically these units will operate a very long time once cleaned up so you really won’t have to work on it much. More than likely the reason anyone needs to work on one of these is because it hasn’t been properly serviced in the first 40-odd years of its life. After it is cleaned up and rebuilt, it probably will work perfectly for another 40 years in a clean home environment.

So we will work on it right in the backbox. Before starting be sure to cover the opening where the cables pass through. You can be sure that you will lose critical small pieces down there if you don’t, and they are a pain to retrieve. I use a customized cover that I made from a piece of cardboard.

backbox hole cover Bon Voyage 1 (resized).jpg

The first step is to undo the unit from the backbox panel it is mounted onto. This is simple enough, just undo two Phillips head screws which attach the unit to the back board. This will free the stepper unit and it can be worked with fairly easily even with the wires attached.

4 mounting screws (resized).jpg

Whenever I undo hardware I like to identify what it is so I have a record in case I lose a piece. For screws I use this handy Nut and Bolt Gauge. Checking these attachment screws tells me they are #8 1/2” pan head Phillips wood screws.

8 nut and bolt gauge (resized).jpg

Actually you don’t have to completely remove the bottom screw since the mounting bracket uses a slot there instead of a hole. You can remove the top screw and loosen the bottom one and the entire unit will slide up and out. I put the top screw back in its hole and screwed it in partway, that way both screws stay right there and won’t be lost.

6 mounting screws removed and stored (resized).jpg

Now you have the entire unit it your hand. You are limited by the wires that are attached but there is a decent amount of space and it can be moved around for access fairly well.

7 handling the unit (resized).jpg

#4 3 months ago

Next the right contact plate (PCB) will be removed. To do this, remove one screw and the hairpin clip as shown by the red arrows. Use a pair of needle nose pliers to grab the round part of the hairpin and just pull it straight off, it comes off fairly easily.

9 ready to remove right pcb labeled (resized).jpg

Now the right contact plate can be moved over and out of the way. There is no need to worry about its orientation as it will only go back into place in one way later. The screw is a 4-40 1” pan head machine screw and there is a black spacer tube that fits in between the two contact plates to keep them separated. The hairpin’s job is to slide into the groove cut into the end of the shaft and hold that in place. These hairpins are generally sized by the size of the opening that fits over the shaft they are going on, which in this case is 1/4” or something close to that. They are also sometimes called hitch pins, retaining pins or cotter pins (although cotter pins generally would have one straight side). They don’t seem to be too common these days but they are out there so if you lose it you should be able to get a replacement.

10 right pcb removed (resized).jpg

#5 3 months ago

Before starting to attack this and take it apart, I like to try to figure out as much as I can about how it actually works. I might learn some more about it when I disassemble it, but starting with as much knowledge as possible can’t hurt. Let’s see what we can sort out from this contraption.


The whole thing is based on a common mechanical device called a ratchet, or ratchet/pawl. These are used in watches, clocks, turnstyles, and all sorts of other things. The main goal of such things is to make a controlled rotation in one direction one step at a time.

The white wheel with the teeth is the ratchet, as it is labeled in the Bally drawing. More typically this would be called the gear as “ratchet” would refer to the whole assembly, but here we will stick with Bally’s naming convention to keep things clearly linked to the drawings. There is a lever called the Drive Pawl which is connected on one end to a steel plunger that fits into a typical pinball solenoid coil. The other end is the pawl which is a tab sitting in a tooth of the ratchet. It is the combined design of the shape of the teeth on the gear and the drive pawl that makes everything work as it should. When the solenoid is activated it pulls the plunger in, this pulls the drive pawl up which in turn causes the pawl to slide along the long curve of the tooth. The pawl then falls into the gap of the next tooth as the solenoid deenergizes and the step-up arm returns to its resting position. This rotates the ratchet one step, or one tooth. The spring is pulling downward on the pawl and it is that spring that helps the pawl to snap into position and thus rotate the ratchet clockwise.

11 internal workings (resized).jpg

There is also a second pawl called the Hold Pawl that is pushed into position between in a tooth gap on the other side of the ratchet. This hold pawl is used as a backlash prevention device to keep the ratchet wheel locked nice and tight into its position. It is held into that lock position by the spring attached to the end. The springs provide the key force to hold those two pawls into their positions. If you remove either of those springs you will see that the whole thing sort of falls apart as the drive pawl and hold pawl will just sort of flail about loosely and the ratchet will not make a clean one-step rotation when the plunger is pulled in and released.

This GIF shows it in action with two steps activated by me pulling up on the plunger and then let it go. Watch it a few times to get how the drive pawl works and how the hold pawl works. Before taking apart the unit, try this a number of times and watch closely how everything interacts, and the operation of the unit then becomes easy to understand.

match unit 1c.gif

#6 3 months ago

Next the hold pawl spring is removed. Take a photo and make a note of how it is attached, but you really can’t miss when it comes time to put it back on, it will go on only one way to get it right. Now the hold pawl will be free to turn into any position.

12 hold pawl spring removed (resized).jpg

Then remove the drive pawl spring in the same way. As shown in the Bally parts catalog drawing, the part numbers for these are SP-100-121 for the drive pawl spring and SP-100-80 for the hold pawl spring. I did not find easy availability of these two springs such as at Pinball Resource or Marco, so it would be best to not lose these. It should be possible to hunt down suitable replacements but that might take some work.

13 ratchet spring removed (resized).jpg

Around the back side of the base plate is a piece of steel with two screws which is called the stop plate. As shown here the end of this plate fits into a tab on a part of the drive pawl. It holds the drive pawl in place and prevents it from falling downard out of position which you can see happen when you remove this plate. It is interested to note that the score counter units don’t use this stop plate. Instead, the drive pawl actually sits right on top of the score wheel and that is what keeps it in position when it is resting. The 2 screws for the stop plate are 4-40 1/8” pan head Phillips with star washers.

14 stop plate view labeled (resized).jpg

15 stop plate removed (resized).jpg

Next remove the two #8 tapered 3/8” pan head Phillips screws holding the solenoid bracket in place.

16 coil bracket removed (resized).jpg

#7 3 months ago

Now the assembly can be separated from the coil and looks like this. Next remove the drive pawl assembly. There is nothing holding it in place, but you will need to move it around it get it out of the various slots and tabs. This is easier if you rotate the ratchet so into the position shown in this picture, with the indented part facing as shown.

17 drive pawl assy removed prep (resized).jpg

17 drive pawl assy removed (resized).jpg

Now you can pull the ratchet straight off. The ratchet was sitting on top of the left contact plate so when it is removed you can pull of that contact plate, and now the entire base plate assembly will be free as well. At this point you can also pull of the small hairpin holding the hold pawl on its shaft and the hold pawl will freely lift off.

18 ratchet removed (resized).jpg

base plate with hold pawl dissassembled (resized).jpg

Now the entire unit is disassembled, and you can proceed with the cleaning of all of the parts to get everything in good working order. Everyone has their own way of doing this, so use my way as a guide or carry on proudly using your own preferred methods.

#8 3 months ago

Here is what the ratchet looked like when originally removed. It is a bit dirty, and the amount of cleaning it gets is up to you. The most critical part is to get the silver contacts on the ends of the wipers buffed and cleaned so they will make good electrical contact with the PCB traces. Note that it is not too critical to get the groove that goes around the edge perfectly clean as it might be if you were doing a score counter unit. That’s because that groove is not used at all for this stepper, that is, there is no rocker arm that fits into the groove to control switch positions like you find in a score wheel. The funny shape of the ratchet also does not come into play on this unit as that is used on a score counter to work the switches. The ratchet gear could be made perfectly circular and without the groove for this unit and it would work the same, but Bally simply reused the existing until rather than having to manufacture a separate part for this unit.

00-90 unit 9 ratchet dirty 1 (resized).jpg

00-90 unit 9 ratchet dirty 2 (resized).jpg

If you want to go all out, you can also undo the wipers on the front and the back of the ratchet. These are held in by #4 1/4” pan head Phillips wood screws. You can remove them without worrying about tracking how they go back together as the two wipers are different and will only go back on in one way. Here you can see that the front wiper as a small bent-down tab that fits into a slot on the ratchet.

ratchet assy dirty dissassembled front (resized).jpg

The back side wiper will go on the correct way when you install it with the contact pins facing up.

ratchet assy dirty dissassembled back (resized).jpg

I cleaned the ratchet in my trusty Harbor Freight sonication bath along with some wiping with q-tips and alcohol and it ended up looking like this.

ratchet front cleaned (resized).jpg

ratchet back cleaned (resized).jpg

#9 3 months ago

The drive pawl was fairly grimy as you can see. You could knock out the roll pin that is holding the steel plunger on the end but I just left it together and also cleaned it in the sonicator and then with some alcohol.

00-90 unit 7 drive pawl and plunger removed and dirty (resized).jpg

drive pawl assy cleaned (resized).jpg

You can also make the hold pawl all clean and shiny as well with the same cleaning methods.

hold pawl cleaned 2 (resized).jpg

The base plate is all steel, it wasn’t too dirty but I cleaned it up with some alcohol and got it nice and shiny. I left the original small paper label on there that says “00-90 UNIT”, this could be replaced with a fancy new printed one if you like. The stop plate was cleaned in the same way.

base plate front cleaned (resized).jpg

The traces on both of the PCB contact plates should also be cleaned. These will be contacted by the nubs on the front and back wipers that are mounted on the ratchet gear. This is the only metal-to-metal connection in this assembly. If everything is cleaned and the contacts finely burnished with some steel wool, it should be good to go. But some lubrication for the metal-to-metal connection would be OK to ensure smooth operation and a good contact. For this I used the Super Lube tube. I used the tiniest amount possible to apply a super-thin layer, and I mean the absolute minimum amount you can put on there. This will give it a nice connection without gumming up the works with lubricant.

00-90 unit 8 ratchet removal 2 (resized).jpg

When putting all the rest of this assembly together, NO other lubricant should be used. Everything is intended to be run dry and clean and it will work best over the long run this way.

#10 3 months ago

The final cleaning step is to clean up the coil assembly. This means cleaning up the mounting bracket and the inside of the coil itself, which will probably be fairly grimy with black dust. And as is typical for this operation, the coil sleeve should be replaced with a new one. The coil on this machine probably was serviced before as it already had a fairly decent plastic sleeve in it as shown at the top of this picture.
18 ratchet removed (resized).jpg

This is compared to a sleeve I had on hand from a Pinball Resource order which is the standard Bally sleeve part number Sleeve-BLY-Standard. As you can see the new sleeve is longer, and you can’t just slap the longer one in there as it might interfere with the fit of things and prevent the whole unit from working properly, which in this case actually does happen (don’t ask me how I know this).

00-90 unit coil sleeve comparison (resized).jpg

So on the advice of a thread somewhere on Pinside, I acquired one of these handy dandy Husky Junior Tube Cutters. Just clamp the sleeve in there and be patient, after enough turns you’ll have it cut to the proper length.

coil sleeve shortened (resized).jpg

The paper wrapping on this particular coil is pretty toasty. Even though this solenoid is energized every time the 10 point relay is activated I don’t think that usage is enough to stress it even after years of use. It only energizes for a brief instant for each hit. I’m guessing that the plunger got stuck in the coil sometime in the past and that’s what overheated, and that’s probably why there was a newer coil sleeve in the solenoid when someone worked on it to fix that issue.

#11 3 months ago


With all of the parts disassembly and cleaned up, it is time for the reassembly of the unit. Will we be able to get everything back together in the right way so everything works perfectly as it should? Yes, we can. As always, just take your time, understand the process, and check as you go and everything will come out fine.

First, slide the hold pawl over its post and secure it with the hairpin. Hold the hairpin with a pair of needle nose pliers and it will push right into its groove, this is much easier than working with a c-clip. The hold pawl only goes on one way, but there are two posts on the base plate so be sure to put it on the right one as shown. That other post is not used in this unit. The hold pawl should rotate freely after it is installed.

1 hold pawl installed (resized).jpg

Next put the ratchet (gear) assembly back together. This is a matter of screwing on the front and back wiper plates. As we noted before, you can’t put these on wrong (unless you really, really try). Find the wiper with the small bent-down tab and fit it to the front of the ratchet as shown. The leftover rear wiper will only go on one way if you logically keep the contact points pointed up as shown.

2 ratchet front wiper attached (resized).jpg

2 ratchet rear wiper attached (resized).jpg

Next take the base plate back to the machine and place the left contact plate of the center post as shown.

5 left PCB mounted (resized).jpg

Now you will slide the ratchet down over the center shaft, and its bottom part will go into the hole on the contact plate and put it into position. Swing the hold pawl around so it loosely sits in its normal position as shown, you do this so you don’t inadvertently get it caught over on the other side of the bent-up tab on the contact plate which is next to it. Then, slide the drive pawl into place. This is one of the trickier parts. It will only go in one way, but you will need to move it around to get it into the right position so that the parts that stick out go into their slots on the base plate, and the end of the drive pawl sits properly on a gear tooth. You can rotate the ratchet gear as needed to get it to fit.

6 ratchet and drive pawl installed (resized).jpg

Once you get it to this point, even though everything is still hanging a bit loose, just give it a test run by moving the plunger up and down to make sure everything moves as it should and nothing is binding.

Next install the stop plate back into position on the other side of the base plate (this could be done earlier in the process as well, doesn’t really matter).

7 stop plate installed (resized).jpg

Next put the springs on as shown. Now is a good time to carefully test the unit. With the springs installed, the hold pawl is now held in its position and the drive pawl also has tension to hold it in place. If you move the metal plunger up and down, the ratchet should smoothly and perfectly make its steps one at a time as you move the plunger. If anything isn’t working right, pull it apart and figure out where it went wrong and then reassemble.

8 springs installed (resized).jpg

#12 3 months ago

Now place the right contact plate into position, fitting the large hole onto the top of the ratchet gear. Then the hairpin can be put into place, and the long screw with the sleeve spacer can be put in. That part is also a little tricky, but its just a matter of getting everything lined up with your hands and then getting the screw threads started, from there its a piece of cake.

9 right pcb installed (resized).jpg

9 right pcb installed 2 (resized).jpg

Now you have the unit assembly all together. Once again test it by moving the plunger back and forth and confirm everything works just as it should. Then you can slide your new coil sleeve into the top of the coil, place the coil in the coil bracket, and screw on the coil bracket. The assembly is complete and all that’s left is to screw the base plate back into place, and the unit is ready to go.

00-90 unit right 3 (resized).jpg

00-90 unit left 1 (resized).jpg

00-90 unit right 4 (resized).jpg

#13 3 months ago

For the final test you can turn on the machine and activate the 10 point relay in the back box. If you have it in Game Over mode then a match light will be lit, and you can confirm that it cycles cleanly through all 10 numbers. When you are testing it this way in the machine, note how rapid and almost violent the action is when the coil energizes, pulls in the plunger, then releases it. It all happens in an instant, and you can see how robust the entire mechanism is. Here is an animated GIF that shows it:

match unit 2b.gif

How many times does the ball bounce off a 10-point switch? Suppose it happens 10 times for a single ball (a conservatively low estimate). That is 50 times for a 5-ball game. That is 50,000 times over a span of 1,000 games. The play meter on this machine had over 70,000 plays on it when I got it, that adds up to 3.5 million activations of this stepper unit! The fact that it takes that amount of mechanical usage and still works reliably over the long run tells you how solid the overall design is.

This completes the description for this stepper unit. If you enjoyed it stay tuned as I work on additional Bally steppers in machine, working my way from the simplest to the most complex, I will post similar descriptions.

#15 3 months ago
Quoted from Skidave:

Nice write up as usual.
I had one of the phenolic contact 'boards' warp causing intermittent match light illumination. The board was warped away from ratchet gear just enough that the contact points were not touching on several numbers. My quick fix was a small zip tie through available holes to pull the assembly together.
I believe this machine was exposed to major humidity that caused this.

I just looked at your post about this. It seems like a reasonable fix, as long as the unit works with that tie wrap why not? Is that board actually warped? Did you try removing it and realigning it? There is a little bit of a weakness in the design because you just have the two points to hold that board in position, the center hole and the lower hole with the screw, so it is off center. The upper part is sitting there kind of loosely.

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