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Thread: Gottlieab System 1 CPU not booting and my introduction :)

  1. #1
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    Gottlieab System 1 CPU not booting and my introduction :)

    Hi everyone.

    I'm new to Aussie Arcade and very new to pinball as well! My interest starts more with Arcade machines, I built my own Mame Tabletop arcade machine from scratch in my last year of high school, I included a photo of it. It had to have a CRT and replicate games as true to the originals as possible, I had alot of making and playing with it!. Now I'm discovering Pinball, and bought my first machine to restore, A 1979 Gottlieb Countdown. I'm pretty good with electronics, and been playing around with electronics stuff since I was really young . But I thought I might find some Pinball enthusiasts who are more experienced on these System 1 machines who could perhaps help me out.

    IMG_0213.jpg

    So My CPU on my countdown is not booting correctly, instead of waiting 5 seconds for the displays to light up and hear the Q and T relays pull in, The displays light up and Q/T Relays pull in immediately! While this sounds like a Slam Tilt condition, it can't be, as I have grounded the slam tilt input and made voltage measurements to make sure Z29 Inverter buffer is grounded on the input and +5V at U3 Slam Input.

    The other strange thing it does, after very close to 60secs you hear the Q/T relays pull in again and the playfield lights go out, only player 1 and the Credit/Balls-remaining displays are lit and flashing quickly a single 0 and this happens indefinitely until you switch it off. If switched back on again, the same things happen and it's always close to 60Secs when the play field lights go out.

    One discovery i made on the CPU board that's bugging me, is making a resistance reading directly between DC ground and the +5V line is a mere 76ohms! surely this can't be right. I have bought another malfunctioning CPU board where this resistance measurement is close to 1Kohms which sounds much more reasonable, could someone with a working System 1 CPU board make a resistance measurement say directly across C16 for me? I have checked all the tantalum caps that go directly across +5V and DC Ground and they are all good, anyone seen this before? My guess is an IC has close to shorted and causing this low resistance.

    Any help appreciated, and look forward to talking with you as I enter the world of pinball

  2. #2
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    Welcome to Aussie Arcade. I am sure someone will chime in soon with some knowledge for you.
    This is where it ends!

  3. #3
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    too many unobtainable chips to bother with this board. its a terrible choice for an electronics project

    suggest you buy one of these https://www.flippp.fr/pi1x4.php to make it work then sell it and buy a bally or williams project to learn on

  4. #4
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    Doug's right about the CPU chips being a big problem but the driver board is repairable which could be part of your problem with the solenoids locked on. Also has the wire harness PCB connectors been re-pinned? If your not sure pull them off & check the pins for a green oxide stain as this is also a problem with system 1 machines. If your CPU board is like this one, take Doug's advise and replace it with a Flippp board, I did & never looked back.

    Gemini2544's 4th Pinball meet Saturday 21/03/2020



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    Thankyou all for your replies. I completely understand why you would steer me away from restoring the CPU board, it has been a nightmare to work on. But despite that, I managed to fix it! For anyone this may help in the future, my problem was Z9, Z8 and Z28 Inverter buffer chips between U5 and the Switch Matrix, only after I discovered a low resistance between two pins on Z9 did I discover this. The fantastic PinRepair website actually covers the fault of General Illumination or Solenoid voltages being shortened to the switch matrix can cause this! I wish I had found that first.

    I now still have one main problem, that the displays can show gibberish, I read this can occur without the RAM Battery, but I have installed a new coin battery and socket and made sure voltage is at the RAM chip, Any other ideas where this might come from? I will ad some pictures soon.

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    Have you checked the contacts on the plug for corrosion.

    Gemini2544's 4th Pinball meet Saturday 21/03/2020



  7. #7
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    Here are some photos of what my displays look like. I found that player 3 display is a faulty ic on the displays board and that's why its very different to the others, I swapped it with player 4 and the fault carried over. But you can see that instead of showing the last high score it shows jiberish, or sometimes nothing, the credit display shows alot of ghosting to. I feel pretty confident that it's not connectors, I haven't replaced them but have cleaned them with Isopropyl, they were very clean when I got it surprisingly.

    IMG_2974.jpg

    IMG_2975.jpg

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