Johnny Mnemonic, Broken Columns, And Pinball Repair


[Quinn Dunki] has come to realize the pinball machines of her youth aren’t the lame games she remembered. They’re actually quite marvelous in terms of electronics, mechanics, engineering and the all important hackability. Wanting to pick up a 90s dot matrix display pinball machine and being a [William Gibson] fan, [Quinn] picked up an old Johnny Mnemonic machine. She’s already looked into replacing the incandescent bulbs with LEDs, and has just wrapped up troubleshooting a broken plasma dot matrix display.

dotsThe neon dot matrix displays in pinball machines of this era are finicky devices with a lot of stuff that can go wrong. On powering the display up, [Quinn] noticed a few columns on the left side of the display weren’t working. These machines have great diagnostic menus, so running a test that displays a single column at a time revealed two broken columns. However, when a solid fill test was run, all the columns work, save for a few dots in the upper left corner. This is an odd problem to troubleshoot, but after more tests [Quinn] realized dots in column five and six only work iff both adjacent dots in the same row are lit.

The power supply seemed okay, leaving the problem to either a logic problem, or something wrong in the glass. With a meter, [Quinn] deduced there was a short between the two broken columns, and tracing every thing out revealed a problem in the hermetically sealed display filled with noble gasses. A replacement display was ordered.

While [Quinn] was replacing the display, she decided it would be a good time to rehab the almost-but-not-quite out of spec driver board for the display. The power resistors had scorched the PCB, but didn’t damage any traces. Replacing the parts with modern components with a higher power rating brought the board back to spec with components that should last longer than the 20-year-old parts previously inhabiting the driver board.

It was a lot of effort, but now [Quinn] has a brand new display for her pinball machine and is ready to move on to the next phase of her restoration.

13 thoughts on “Johnny Mnemonic, Broken Columns, And Pinball Repair

      1. My favorite machine is the classic Williams PIN•BOT, a nice complex table with multiball and everything, before the age of DMDs and all the newfangled electronic bells and whistles. (And now that I’ve looked that up, I just learned of ‘The Pinball Arcade’ and have something else to sink my non-existent cash into… T_T)

      2. A Dr. Who pinball machine could be anything from a steam-powered William Hartnell model to a Kinect-controlled 3D-TV-projected Matt Smith version with a 3D-printed sonic screwdriver.

        The pinball machines of my youth were mostly electromechanical, and my college years were back when the drinking age was 18, so it was possible to get a beer at the student union pub and drink it while playing pinball. Much better than the pinball machines at the bus station, which only gave three balls per coin instead of five, and were tuned to be much harder to get an extra ball compared to the ones at school.

  1. Thanks for the post, Brian! Poor Johnny has been fighting for every inch, but he’s coming back to life little by little.

    Johnny Mnemonic is arguably the best value in pinball. It’s a deep ruleset, high speed DMD machine from the golden era of Bally Williams with better gameplay than most A-list games, for one quarter the price. It has deep strategy, a ton of Easter eggs, and what many consider the best wizard mode ever made. People overlook it because the movie was…what it was. They only made 2756 of them, so I’m happy to get one fighting fit once again.

    George Gomez is the king of speed, and he proved it with this game.

    1. The Johnny Mnemonic at our local hipster bar/pinball league hangout is the least favorite of the eight machines there, I’m afraid, but that’s mostly because a number of play field lights are burnt out and it’s in a dark alcove. The result is that it’s very hard to see where the ball is, and since the ball moves at about warp eight, it makes the game rather challenging in ways not designed. (Also the glove prop doesn’t quite work — it moves backwards but not forwards — but that’s only a problem if you can see the ball well enough to send it to the glove.)

  2. I’d be interested in the “bad” display, it is certainly salvageable for my purposes.
    How much coin of the realm for shipping to the Channel Islands please?

    also might be repairable with a focussed BRD laser, this technique works with dodgy valves apparently although I haven’t ever tried it on a display like this.

  3. The bad display may be recoverable by discharging a capacitor through the short and vaporizing the offending material. Most likely it is just a tiny amount of sputtered metal, or some small piece of dislodged and lodged again contaminant.

    Same, more risky, can be achieved with a high-current power supply (e.g. lead-acid battery), but that brings the risk of overheating the substrate or the electrodes and cracking the glass.

    1. A cap zap, maybe a piezo igniter, maybe a little mechanical force applied in just the right direction, but all could be risky. But since this display is bad and a new one can be had, I’d say no harm in trying.

  4. “A quick reminder about safety. In addition to the high voltages, the DMD power supply can source substantial current, in the range of 2-3 amps. This is sufficient to murder you quite dead.”

    No it isn’t. My career is fixing pinball tables and I can tell you now, although it might nip you, a DMD certainly won’t kill you.

    Also converting these tables to use LED lamps is generally a bad idea. For one, the artwork was designed to be illuminated with incandescent light, so when lit with LED they can look very ‘cold’. Also the lamps are hooked up in a matrix, meaning they get scanned once every few ms. LEDs will flicker, causing a strobing effect which isn’t ideal on a game that requires quick reflexes. Incandescents ‘glow’ for a short while after the power is turned off so don’t suffer from flicker.

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