This "Pfutz's Programming experience with hardware" applies to:
Breakshot Pinball

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Pfutz's Programming experience with hardware

"Phantom Switch issues"
or
"Detecting shorted diodes in a Switch Matrix"

Disclaimer: Remember that are getting hardware advice from a software person, would you let your grocer repair your house?


Note: I highly recommend reading Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Three and search for section "When things don't work: Switch Matrix". It covers lots of switch issues. This article only discusses a shorted diode issue!

Switch Matrix Theory:
Breakshot is the only Capcom game to use a switch Matrix using a standard 8x8 X-Y matrix for 64 switches. (However, lots of "other" manufacturers use a switch matrix, and this applies to all of them too!) And an additional 16 direct input switches from the CPU, for a total of 80 switches! All the other games (Pinball Magic, Airborne, Flipper Football, King Pin) just use direct switch inputs and do not use or need a diode! A switch matrix REQUIRES a diode in series with the switch. If the diode is shorted or missing, it can cause other switches to mysteriously act like they have been activated. Sometimes this effect is called "Phantom switches" (for the switches that act activated, but in reality were not activated) For a switch matrix we electrically drive one column and read 8 rows at a time. This is repeated for each of the 8 columns (until all 64 switches have been read). The diodes in series with each switch prevents a back current in the matrix from other closed switches that cause "Phantom switches" in other rows or columns.


The Breakshot manual diagram on page 142/148 shows the switches in series with the diode.
At the bottom of this diagram, it shows you the 2 kinds of switches that Breakshot uses: Opto's and Micro switches. I am pretty sure it also uses a few leaf switches!

For a Simple Leaf Switch, there are 4 terminals:
Here are the leaf switch connections:
  • The Front terminal or lug, only the banded side of the diode is connected here! This is one side of the leaf contact.
  • The Middle terminal or lug, the row or Red-??? wires are connected here! This is another side of the leaf contact.
  • The Back terminal or lug, the non-banded side of the diode and the Wht-?? wires are connected here! This is an isolated terminal.
  • The isolated Mounting lug, this is not supposed to be connected to anything.

    Now when I say shorted diode, there are 4 terminals on any leaf switch. If you mistakenly repair a switch and attach the White column wire to the front terminal, you have effectively taken the diode out of the circuit and made it look like a shorted diode! (causing lots of these types of problems). Sometimes this happens because the diode is on backwards or someone just soldered the wire on the wrong terminal.

    Other issues are:
  • Another wire or metal part is touching any metal or wire part on the switch!
  • The diode (which hangs in the air) is twisted and the wires are actually shorted together or are touching some other wire.
  • In the extreme cases, the isolated lug(s) is/are internally shorted to one of the 2 other lugs.
  • In the extreme cases, the isolated mounting lug is internally shorted to one of the 2 other lugs and/or is touching another wire!

    For a Simple Micro Switch, there are 3 terminals:
  • N.C. (Normally Closed Contact), this is the WHT-??? wire and the non-banded side of the diode.
  • N.O. (Normally Open Contact), this is the RED-??? wire.
  • COMM. (Common Contact), this is the banded side of the diode (no other wires!).

    When you first look at this, you might ask "Why do they use the N.C. contact? Wouldn't this short out the diode?". And the answer is: Micro switches are designed to ALWAYS "break before make". Or in other words, there is always a "middle" position (i.e. a closed position, a middle open circuit position, and an opened position). Whenever the contact moves from open to closed (or closed to open), they ALWAYS go through the middle "open circuit" position. This prevents both contacts (N.O and N.C.) from momentarily making an electrical connection at the same time. The benefit is that we do not electrically use the N.C. contact, so when the switch is connected to the N.C. contact (and the diode is shorted) we have the overall electrical switch circuit in the opened state, and since we only use the diode when the switch is closed or the contacts are in the N.O. position, the diode will not be shorted at that time. Thus, we do not care if the diode is shorted on the N.O. contact, so we have a spare lug that can be used to hold the diode and a wire!

    However, back to a real shorted diode. Typically there can be the same issues as before: If you mistakenly repair a switch and attach the White column wire to the "COM." terminal, you have effectively taken the diode out of the circuit and made it look like a shorted diode! Sometimes this happens because the diode is on backwards or someone just soldered the wire on the wrong terminal.

    Other issues are:
  • Another wire or metal part is touching any metal or wire part on the switch!
  • The diode (which hangs in the air) is twisted and the wires are actually shorted together or are touching some other wire.
  • In the extreme cases, the mechanics inside the micro switch are bad or broken, this can easily happen when bracket screws that hold the micro switch are too tight and they crush the delicate plastic switch! (please be careful with power tools! or do not hand overtighten!)

    For a Simple Opto Switch, there are 2 parts:

    ALL Opto switches send an infrared (IR) beam of light from a "transmitter" to a "receiver". Optos with small distance (say about 3 inches or less) do not need any fancy modulation in the "transmitter" and a fancy modulation detector in the "receiver". Humans cannot see infrared light. But you can use IR equipment to help you see this light. An now, most common digital cameras show infrared light! Just point your camera at an IR remote control (i.e the remote control for your TV) then press a button on the remote control, you should see the "transmitter" blink or go on. If an opto fails, you do not know if the "transmitter" or "receiver" failed. Well, now you can see if the "transmitter" is working with your digital camera. The camera "sees" the IR light just like you would see a flash light when you shine it in your eyes. However, like a flash light, the camera cannot see the beam of light traveling in the air, until it is reflected off of something. So you can use a small piece of paper to "follow" the beam to the "receiver". Now it is important that the "receiver" be completely covered with infrared light. If not, you have to re-aim the "transmitter" or "receiver". There are many different kinds of Opto boards (see above).

    Note: the below diagram in the Breakshot manual is a little misleading. The "receiver" is not connected to +5V and ground, instead it is connected to the switch matrix. And the title note says that the opto board is only the dashed lines. So I have re-drawn the connection to the switch matrix to the right of the red "X".


    Oh and another thing about opto's, when they are working, and a ball is not blocking the beam, they normally look like closed mechanical switches (instead of mechanical switches which are normally open switches). Let me repeat, it is important to realize that working optos normally look like closed mechanical switches!

    Any ways, an opto "receiver" electrically looks like a diode, the only way I know how to short this "diode" out is to blow up (or "let the smoke out" of) the "receiver" (which makes it not work at all...). Or in Plain English: opto's cannot have shorted diodes.

    Other issues are:
  • Another wire or metal part is touching the circuit board!
  • Connectors are not on all of the pins.
  • Power is missing to all or some "transmitters" (i.e. a blown 12V fuse with would effect all optos, use the "C1-02: OPT0 TEST")
  • Vibration has broken one wire at the bottom of a "transmitter" and/or "receiver". The broken wire is located in the middle of the circuit board (between the part and the soldered wire to the PC board). Making it impossible to visually see the broken wire!


    For a Electronic proximity sensor) Switch:
    Again Breakshot, from the factory, did not use any proximity sensor(s). However, if you spare no expense, they are supposed to be the most reliable switch. In theory, they at least 4 wires: power, ground, switch row, and switch column. If there are any proximity sensor(s), you will have to look them up on the internet...

    Now Identify the "good" and "bad" switches
    One test to identify the switch for a shorted diode is to close ALL possible mechanical switches (maybe use painters tape or masking tape to hold them closed) and make sure all optos see the IR beam. Then open a mechanical switch one by one, until you find a switch that does not open (this is the switch with the shorted diode). You should use the diagnostic "C1- 01 Switch Test" as it makes a sound when switches ELECTRICLEY open or close and also shows you graphically what switches are opened and closed.



    Good Luck!
    Pfutz

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