Parts that wear

Mixers

Mixer assembly
bikini

Like the drag arm stops, this problem is also subtle, and to some extent theoretical. The mixer discs randomize the game and control the odds such that the game operator will make money over the long term (this is known as percentaging, and is why Las Vegas exists).

The mixer operation is pretty simple. When a coin is played, the mixers are released to spin by activation of the mixer latch coil(s). After some time (related to those cams that the drag arms where mucking with), the mixer latch coils release and the mixer lever arms slide up, the index pins catch the mixer discs and stop them from spinning.
The sneaky bit is the lever arms themselves slide at different times relative to each other, thus causing the discs to stop at different times.

Mixer Roller and Cam

a roller on the lever arm which the cam rides on
lever arm roller

As usual, the variable timing of the lever arm sliding is accomplished by cams. When the mixer latch coils energise, the lever arms slide down, and a notch catches on a metal plate. When the mixer latch cams release, the lever arm stays caught on a notch until a cam pushes the arm off the notch and a spring pulls the the arm up, thus engaging the disc.

Anyway, here we have a roller on the lever arm, and we can see that the roller is not perpendicular to the arm. In fact, it wobbles around, but in actual use it is pushed back so the cam is riding on it's surface at an angle.

Well, obvious wear...
roller axle

In the interests of science, I removed the roller so we can see that the actual wear is on the pin which is acting as an axle. The only choice here is to replace the whole arm, or replace the pin. The pin is part of a piece that is pressed onto the arm permanently. You can drill out this piece and replace it with a length of 1/8" steel rod which you can get at a hardware store. You also need #5 washers. I found the rod, but the washers were trickier. You can find some over by the pop rivets. I removed the entire press-fit piece, which resulted in a hole larger than 1/8". Here is where expoxy works...just make a sandwich out of washer-arm-washer with epoxy in between, and stick in a piece of the rod. If the washers are cupped, make the curved faces touch the roller. As the epoxy sets, make sure you have the pin as perpendicular to the arm as possible. When the epoxy dries, make sure none is on the pin itself. Wait a day for the epoxy to harden, then stick on the roller, and another washer. Epoxy this washer onto the rod, and trim off extra rod after it all dries. There's other ways to hold the roller onto the rod if you can find pieces small enough (clips, caps, etc). A moto-tool with a cutoff wheel is pretty handy for this job.

Of course, the main question about wobbly rollers is "so what". Well, let's take a look at the cam that rides on this roller....though this is NOT a common problem.

pretty ratty
mixer cam

This cam was originally symmetrical. It's actually pretty badly worn... the wear has turned the cam lobe into a ramp. Imagine the roller on the edge of this cam...the cam would be rotating clockwise, and the roller would climb up the hill slowly. Hopefully someplace near the top of the lobe the arm will disengage from the notch and slide up to stop the disc from turning. If you imagine the cam rotating counter-clockwise, you'll see how it originally worked. The roller climbs a much steeper hill and therefore disengages the notch faster.

Part of the reason for the excessive wear is that the cam edge is no longer flat...it's got a bevel caused by running along the skewed roller surface.

So what to do about it. Well, if the cam still works, I guess you stick it back in and forget about it. The difference between the original steep hill and the worn slope doesn't really matter at all - it may cause the rotor to spin 1-2 additional positions before it is stopped, but that's about all.

Another option is to replace the bakelite cam with one from a parts machine. If you are truly desperate, you'd have to make a new cam. John found a source for phenolic canvas sheet material - www.professionalplastics.com, but you'd only need a tiny piece. Probably easier to go to a retail plastic place like Tap Plastics, get a piece of scrap acrylic and carve out your own.

Mixer Arms

mixer arm diagram
green book

Notice how the arms (15 - although the one they point at is different from the rest) slide in a slot in a metal plate (32). The diagram shows the arms in their "stop the disc" position. You can't see the notch. However, if you imagine the arm sliding down, the notch (see picture below) will catch on the plate and keep the arm from sliding back up.

no notch any more
lever arm

The cam and roller aren't normally going to be your problem. The notch at the top if the lever arm is going to have the same kind of wear as the drag arm stops. Over time, the metal wears down and the arm no longer catches on the plate. When the mixer latch coil shuts off, the arm immediately slides up and stops the mixer disc.

There are two solutions - the correct one and the one the operators normally chose. The correct one was to replace the arm. Since that costs money, the operators generally did what you are about to do..they filed the metal to recreate a nice notch. However, there are limits.

If you remove too much metal, it won't work. Either the arm will slide up far enough to stop the disc before it should, or the cam will push the arm off the notch before it should.

This guy overdid it.
filed lever arm

This is the top of the arm corresponding to the above worn cam. Some guy got happy with a file, and he took off way too much metal by making the notch deeper and longer. Why this helped cause the cam wear isn't obvious. The tension on the spring that slides the arm up (37) is stronger due to the deeper notch, and because the notch is longer, it never was held away from the cam by the metal plate (32). When the cam pushes the arm off the notch, the only part of the cam which is supposed to be touching the roller is the top of the cam lobes. By lengthening the notch, the roller is always riding along the cam!

The only solution at this point is to replace the arm or replace the metal by welding it. I saw a GI-Joe junior welding kit at a hardware store for about $50. It uses some stuff called Mapp Gas and oxygen, and I tried it. It produces a nice little flame that is good enough to make the metal red-hot, and I used some kinda brazing rod to form a big blob of metal where there was no metal before. The tricky bit is that metal is a liquid when it's melted (duh), so you need to figure out a way to hold the arm and apply the new metal so it doesn't run away in a direction you don't want. I used a bench vise. The other nasty bit is the torch itself is shooting out a flame under pressure, so it wants to push the liquified material away. A little experimentation and will eventually get a blob of metal where you want it. Don't try and be neat...you grind off the excess after it has cooled using you trusty moto-tool with cutter attachment.

The open question is how soft is brazing material...will it wear away much faster than the original material?