Electromechanical Pinball Machines

I’ve been working on a lot of EM (electromechanical) pinball machines lately. I usually don’t write about them here because the repairs don’t make for interesting reading and wouldn’t be very helpful to owners of other pinball machines.

Electromechanical pinball machines are the ones with the score reels instead of digital readouts, and have chimes and bells instead of electronic sounds. These machines use mechanical motors and stepper relays instead of digital circuits. It’s pretty amazing what they were able to accomplish using mechanical devices before the digital age.

As pinball machines become more popular, many of these old machines are being pulled out of storage and need a little TLC to get them up and running again.

Some of the EM pinball machines I’ve worked on recently are:

Dealer’s Choice (Williams, 1974)
Straight Flush (Williams, 1970)
Aladdin’s Castle (Bally, 1975)
Bally Hoo (Bally, 1969)
Super Star (Williams, 1972)

There are two common problems that most EM machines have: Dirty or mis-adjusted contacts or gummed up stepper units or score reel mechanisms.

There are hundreds switch contact points in an EM machine. Usually about one percent of the contacts are dirty or out of adjustment. What happens is the contact will get some dust on it. When the contact opens or closes, it sparks, which turns the dust into carbon. Carbon acts as a resistance, reducing the amount of power flowing through the contact. If the carbon build-up is substantial enough, no current will flow through the connection when the contact closes. Sometimes the current will flow through the contact generating heat, which is my theory on why they get out of adjustment.

The second most common problem is gummed up stepper units or score mechanisms. Usually the manufacturer put a thin layer of grease on the disk contacts. Over time this grease gets dirty and also turns into a sticky gel. The solution for this is to clean/rebuild the steppers.

I often get asked about the value of an EM pinball machine. Looking at the Mr. Pinball 2014 price guide, most EM pinball machines I’ve encountered are worth about $500, give or take, in very good condition. The items that affect the value the most are cosmetic, such as the playfield paint and wear, the backglass paint (which often peels), and the cabinet paint. These are the same things that affect the value of a solid state game, except supply and demand plays a bigger role.

Most of the time, electromechanical pinball machines are worth fixing, especially if the cosmetics are good.

Aladdin’s Castle, Bally Pinball Machine, 1976

Location: Longmont, CO.

Symptom: Pinball machine wouldn’t reset.

I visually checked the most likely relays and contacts: Game Over, Coin, and Credit.  After not finding any problems with the relays, I checked the switches on the score motor unit.  I noticed that the motor was hot and was obviously energized, but not turning.  The cams rotated freely but the electric motor itself was seized.

I disassembled the motor and managed to get the seized shaft out of the bearing. I cleaned both shaft and the bearing, but there was still some type of corrosion on the shaft that was preventing it from turning freely.  I would have preferred burnishing the shaft with some very fine 0000 steel wool, but I didn’t have any on-hand.  I used some 800 grit sandpaper and removed the corrosion (or whatever it was).  I lubricated the bearing and the shaft so that it slid and rotated freely.

After reinstalling the motor into the scoring unit, the machine reset correctly when pressing the start button.

The scoring motor and switch bank assembly is basically the heart beat that runs an electromechanical game.  Without it, nothing will work.

We (the owner and I) noticed that the Ball In Play lights were not resetting back to Ball 1 during the reset.  I checked the stepper in the backbox and saw that it was sticky, which is a common problem.  It didn’t seem sticky enough that it warranted rebuilding. The Ball In Play stepper unit is a step-up and reset type. The owner cleaned the old lubrication from the contacts and I added a turn on the spring.  The stepper seemed to function fine after that.  I informed the owner that if problems continued with the ball counter, that it would have to be cleaned and re-built.

We replaced some burned out lights on the playfield and talked about playfield care.  I mentioned that a lot of collectors have differing opinions, but that I liked Novus 2 for playfield cleaning and polishing.

As for me, I’m going to start carrying 0000 steel wool in my repair kits for cleaning up motor and stepper shafts.  It has worked well with jukebox restorations I’ve done.