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Thread: (SOLVED) Need help fixing old Lloyd's gaming pong machine video included!

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    Default (SOLVED) Need help fixing old Lloyd's gaming pong machine video included!

    Been trying to get this console working off and on for a while now and ready to get it out of my shop. Got the console all cleaned up but I am having problems with one of the paddles showing up black instead of white and haven't been able to find much info on it. Please watch the video to see what I've done and maybe give me suggestions on where to go. Thanks I look forward to reading yall's comments.

    https://www.youtube.com/watch?v=Q3Pv202DHNQ

    Pin out of pong chip....
    https://upload.wikimedia.org/wikiped...500_pinout.png
    Last edited by kream_dream; 12-02-2017 at 08:57 PM.

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    ServBot (Level 11) jb143's Avatar
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    That second chip is just a NAND gate, it's basically being used to combine the video from the paddles and ball video outputs. Since everything else seems to be otherwise working, and you replaced the chips and caps, I would check continuity between those 2 chips to make sure that the signal is even getting there. Or check it with a logic probe compared to the other paddles pin.

    Maybe reflow the solder as well, and on the jumper and anywhere else that carries that signal.
    "Game programmers are generally lazy individuals. That's right. It's true. Don't let anyone tell you otherwise. Since the dawn of computer games, game programmers have looked for shortcuts to coolness." Kurt Arnlund - Game programmer for Activision, Accolade...

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    Quote Originally Posted by jb143 View Post
    That second chip is just a NAND gate, it's basically being used to combine the video from the paddles and ball video outputs. Since everything else seems to be otherwise working, and you replaced the chips and caps, I would check continuity between those 2 chips to make sure that the signal is even getting there. Or check it with a logic probe compared to the other paddles pin.

    Maybe reflow the solder as well, and on the jumper and anywhere else that carries that signal.
    Thank you for your reply! I did replace the chips and the 3 electrolytic caps. I had good continuity from the pong chip to the nand gate but just to be sure I soldered a wire directly from one to the other with no effect. I did as you suggested and reflowed the solder as well. I don't have a logic probe but now I guess I will look up what one is and see if I need one lol! I love buying new tools just low on cash atm. If you have anymore suggestions please say so and I will give it a shot as I'm at a stand still and just grasping at straws.


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    While looking for a schematic I ran across this old thread in which several people mention the same problem with different pong systems. (It's odd that it's always one of the paddles and never a ball or the playfield)
    https://forum.digitpress.com/forum/s...gely-need-help!

    No verified solution though, but it does show a general pong schematic.

    All of the schematics I've found for pong systems show diodes instead of NAND gates, including that thread, though it does mention that some systems use NAND gates instead of diodes. The idea is the same though, take several different signals, one for each "object" to be displayed, and mix them with the sync signal to get your video signal. So the problem has to be somewhere between that paddles output and the point where they are mixed. Since you jumped the signal wit no effect then it's probably either the signal itself(not as likely if you tried a different chip and had the same problem) or in the output of the NAND gate.

    A logic probe is just a device that shows if a signal is high or low or pulsing(which is probably what you'd be looking for). Or a signal tracer would work better. Some higher end meters include a signal tracer setting. Or an oscilloscope would be even better. If you compare the path of the good paddle to the bad paddle you should be able to see where it drops out.
    "Game programmers are generally lazy individuals. That's right. It's true. Don't let anyone tell you otherwise. Since the dawn of computer games, game programmers have looked for shortcuts to coolness." Kurt Arnlund - Game programmer for Activision, Accolade...

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    Quote Originally Posted by jb143 View Post
    While looking for a schematic I ran across this old thread in which several people mention the same problem with different pong systems. (It's odd that it's always one of the paddles and never a ball or the playfield)
    https://forum.digitpress.com/forum/s...gely-need-help!

    No verified solution though, but it does show a general pong schematic.

    All of the schematics I've found for pong systems show diodes instead of NAND gates, including that thread, though it does mention that some systems use NAND gates instead of diodes. The idea is the same though, take several different signals, one for each "object" to be displayed, and mix them with the sync signal to get your video signal. So the problem has to be somewhere between that paddles output and the point where they are mixed. Since you jumped the signal wit no effect then it's probably either the signal itself(not as likely if you tried a different chip and had the same problem) or in the output of the NAND gate.

    A logic probe is just a device that shows if a signal is high or low or pulsing(which is probably what you'd be looking for). Or a signal tracer would work better. Some higher end meters include a signal tracer setting. Or an oscilloscope would be even better. If you compare the path of the good paddle to the bad paddle you should be able to see where it drops out.
    Ok well atleast I got something else off the list. I pulled pin 9 and 10 of the pong chip out of circuit and swapped them, doing so made the left paddle visible but the right paddle was not. So I guess this just confirms my suspicion that the pong chip is working fine its something to do with the circuit for the left player output after that. I will try and take a better look at the NAND gate and see whats going on. I wish I could find a schematic for this console but have had no luck googling anything.


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    Got it! I found a pinout for the NAND gate. Pin 10 out of the pong went to pin 6 and 5 of the Nand gate which were "1b" and "2b" in so from pin 4 which as "out b" it went to a 30k ohm resistor and then into the video circuit. I de-soldered the resistor and ran it from the bridged pin 5 & 6 straight to the video circuit and voila! Thank you very much for your help jb143! I have no idea why it doesn't work through the NAND gate (especially since I replaced it with a new one) but I am fine with bypassing it as long as it works. Hope this helps somebody in the future.




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