THE SCORE MOTOR
Before continuing on with a schematic analysis, it really pays off to consider the score motor in some detail first. The score motor is integral to many of the subcircuits in an EM pinball machine and if you have a good solid mental image of how it works it becomes much easier to decipher and understand circuits.
The Score Motor, shown in the picture below, consists of a series of cams on a shaft which is connected to a motor that rotates the shaft, and therefore the cams. Mounted on top of the cams are stacks of switches. When the Score Motor is resting all of these switches are in their default POGSUP state as drawn in the schematic. Some are NO and some are NC. Each cam has a different shape via some protruding lobes so that as it rotates, it causes the switch stack above it to swap states as the cam rotates. This means all of the NC switches on the stack will open and all of the NO switches will close. The various cam shapes are used to provide timing for the switch changes as the motor turns, or to provide multiple pulses for some switches. The Score Motor looks intimidating with all of those switches and wires, but if you work on it logically one step at a time you can figure it out.
This drawing from the Introduction to Bally Flipper Games document shows the shapes of the score motor cams.
score motor drawing (resized).jpg
Also included in that guide is a description of how the cams relate to each other. It seems a bit confusing when you first read this, but it actually does make sense once you relate it to how the cams are shaped, which we can elaborate on.
score motor bally description (resized).jpg
The Score Motor itself is shown below in the schematic highlighted in yellow, in its normal resting state. It is connected across the 50V leg of the power supply like all action circuits are. If you look carefully at its circuit you can see that normally there is no connection to between both legs of the 50V supply, so the motor doesn't have power to run, it just sits motionless.
There are a number of switches that are found in the score motor circuit such as Evens Hole Relay, Odds Hole Relay, Bonus Score Relay, and so on. These are all wired in parallel between the score motor power input and the 50V supply line. So if any of these switches closes, the score motor will get 50V and it will start turning. As an example below, the Evens Hole Relay has been closed and as shown it now completes the 50V circuit to the score motor, which then will make the score motor start turning. Any of the other switches in the parallel chain will work the same way to start up the score motor, but the problem with any of them is that they are typically just closed for a short period of time. We need to have a longer AND controlled duration for the score motor in order for everything to happen in an orderly manner as is necessary for reliable operation.
There is one special Score Motor switch on the first cam that controls the Score Motor itself. This is switch 1E (also yellow) which is actually a make-break switch. One half of it is Normally Open at rest. The Score Motor can be triggered to start running by a variety of switch inputs. Once it starts turning, switch 1E will immediately move to the other position which due to the shape of Cam 1 then provides continuous power to the motor, keeping it turning. Thus, the score motor takes over and powers itself. This is needed because the switches that trigger the score motor to start are generally only closed for a short duration, so on their own they would only move the motor a small amount. But we need it to make a complete half-turn for everything to work right, and that is the job of switch 1E. Once it has rotated around 180 degrees (halfway), the shape of the cam is such that switch 1E will move to the opposite position or back to its NO state, which cuts off the power to the motor and stops it, unless there is still some other input telling it to go. Thus, the Score Motor is naturally set up to make a one-half revolution whenever it gets a signal to go. During this turn all of the switches will move up and down with their cams and every switch will change states, that is, all NO switches will close and all NC switches will open. But each switch will only make something happen if it is connected via some other switch in the entire circuit within a specific subcircuit. By going through the entire circuit diagram as we will do here we can eventually figure out all of the actions of the score motor.
score motor circuit resting (resized).jpg
These next 2 diagrams show how the score motor cams work to cause things to happen with different timings. First is the Sequence of Operation of Score Motor Switches which is shown on the Bally schematics. This gives you a picture of how each cam changes state for each half-rotation of the score motor.
Monte Carlo Schematic Sequence Operation Score Motor Switches (resized).jpg
Next here is another way to look at the same information. This is in the form of a pulse diagram. The shapes of the 12 cams are shown on the left and this is translated into their timing as they rotate. The dashed lines represent the two "parked" positions of the score motor, when switch 1E is in the rest position as described above.
score motor cams (resized).jpg
Use any of these pictures or a combination of them to get the image of how the score motor timing works. If you know how a pinball machine works, it should start to make some sense if you think about the layout of the timing.
- Cam 1 is used to control the score motor itself as we have seen. It can also be used for any situation where we want a switch to change state the entire time the score motor is turning.
- Cam 2 provides a series of 5 pulses in a row. This is handy for 5X scoring events, for example if you want to score 500 points there is no 500 point relay, but you can trigger the 100 point relay 5 times and to get this. This cam is also used for situations where a lot of pulses are needed to get something taken care of, an example being resetting the score reels at the start of a game.
- Cams 3-8 each just give one pulse, but these are staggered in relation to each other. These can be used to control the timing of events, for example if you want some things to happen before another, then put the earlier events on the lower number and the later events on the higher number.
- Cam 9 gives 3 pulses, so it can be used to give scoring such as 300 or 3000 points.
- Cam 10 gives the latest signal at the end of a score motor turn so it is used for things you want to happen last.
- Cam 11 provides 6 pulses that are slightly offset from the other cams, it is used mainly for adding credits but can also be used for score reel reset operations.
- Cam 12 acts as an alternator, so the switches will be in opposite states every time the motor makes its half turn. For example there might be two pop bumpers that switch between 10 points and 100 points "randomly" in this way.
All of these examples will be described in detail in the circuit analysis.
The last piece of the score motor puzzle is the switch naming protocol. The switches are labeled as SCM switches and they are labeled by their cam position and their position in the stack of switches on that cam, with A being on the bottom and going up the alphabet from there. So SCM4A is the bottom switch on cam 4. SCM8C is the third one up from the bottom on cam 8.
Added 72 days ago
Important note about the Bally score motor: There are typically slight variances in the order and the function of the cams from machine to machine, so be sure to analyze the specific score motor layout for each machine you work on. (Thank you to MarkG).