Modifying the ping-pong game to video out

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Modifying the ping-pong game to video out

Postby Henzelmen » Wed Jul 08, 2020 8:46 am

Hi everyone, this is Hans from the Netherlands,
I think I could use some help from your knowledge of video signal, Horizontal and vertical sync signal and mixing these.
What is my problem:
In the attic I found an old ping-pong video game with an RF output. Unfortunately this rf output no longer functions properly so I thought, I modify the output and make it suitable for video output. And I need help with this because my knowledge of video, sync, black burst, luminance etc are unfortunately not enough to get this done.
I explain how the ping-pong circuit works ...
The game is from the 70's so it is quite simple, the whole works with one ic and that is the AY-3-8500. There is a lot to read about this ic on the internet because I am not the only one with this idea, so I have tried some circuits but unfortunately there is nowhere a good description of how to get a clear picture, there is certainly a video picture but very dark, so I think the luminancy should go up? But whether this is possible or not and how to manage that I would like to hear from you.
Attached is a diagram of ic AY-3-8500 in which pin 6, 9, 10 and 24 are the image outputs and pin 16 is the sync output. In the diagram, these are connected to each other via a resistance network, but surely there should be a nicer solution for this?
Anyway, please check the schematics and hopefully someone can help me with a solution.
The complete book with the discription of this ic you can found here ....
http://www.pong-story.com/GIMINI1978.pdf
If you have any questions please let me know.
Thanks in advance for reading.
Attachments
Ball & Paddle.JPG
Datasheet AY-3-8500
System diagram.JPG
System diagram
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Henzelmen
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Re: Modifying the ping-pong game to video out

Postby Steve Anderson » Wed Jul 08, 2020 6:17 pm

Hi, and welcome to the forum...

Though this is somewhat off-topic I'll help where I can. First thing is can you measure the voltage between the Vcc an Vss points shown in the circuit (extreme left side) - I assume it will be about (close) to 5V. I suggest disconnecting and removing if possible the faulty modulator first. Let me know the result. If you can't remove to modulator, never mind, leave it in place.

If that is the case all it will need is the addition of one transistor, three/four resistors and one electrolytic capacitor.

This will give you a baseband video out, not RF modulated, which I think is what you want.

Do you have access to an oscilloscope?

Steve A.

Postscript - Reading the datasheets it appears it might be 6V, not 5V which is no problem...
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Re: Modifying the ping-pong game to video out

Postby Henzelmen » Fri Jul 10, 2020 8:20 am

Hi Steve,
Thank you for the fast response on my question, this weekend I will try your suggestions, at the moment to busy for the hobby unfortunately and won't do this in a rush.
Ill come back at you as soon as possible.
btw. I do have access to an oscilloscoop.

Greetings,
Hans
Lekkerkerk, Netherlands
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Re: Modifying the ping-pong game to video out

Postby Steve Anderson » Sun Jul 12, 2020 5:31 pm

No problem, do it when you have the time...

Looking at this again it is possible to do this with just a change of two resistors, no transistor or capacitor required....

If the monitor or TV has a standard 75 ohm baseband composite video input (not RF), or a YUV (Y,Cr,Cb) input use the Y input, ignore the others.

Change the 220 ohm resistor connected to 0V/ground to 300 ohm (or 2x150 in series).
Change the 510 ohm resistor feeding the modulator to 75 ohm (or 2x150 in parallel).
Disconnect the input to the modulator. That 75 ohm resistor (or 2x150 in parallel) which would have fed the modulator is now the output to feed the monitor or TV.

Steve A.
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Re: Modifying the ping-pong game to video out

Postby Steve Anderson » Mon Jul 13, 2020 1:33 pm

The above all done with Thevenin's Theorem-, all classical electrical/electronics textbooks will cover it...

https://en.wikipedia.org/wiki/Th%C3%A9venin%27s_theorem

Steve A.

However, the output voltage may still be a bit low due to the limited current drive of the 4072. If that is true then we may have to add the transistor and capacitor as mentioned before. Let's see how the above performs.
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Re: Modifying the ping-pong game to video out

Postby Steve Anderson » Mon Jul 13, 2020 4:52 pm

Having run a simulation on this, just remove (open-circuit) the 220 ohm resistor to ground, no need to replace it with anything. All the rest unchanged from the above..

The limited current drive of the 4072 is the problem, but it should work....he hopes...

Steve A.
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