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Ultra Pong not switching to 2 player mode


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I have an Ultra Pong that is mostly working, but it is stuck in the 4 player mode and will not switch to the two player mode no matter how many paddles are not plugged in.  Also, the Right B paddle will not move the cursor.


Here is what I have tried so far:

1)  All 4 of the paddles will work in any of the Left A, Left B, or Right A jacks, so I know it is not a problem with the paddles.  They all range from about 0 to 800 kOhms.

2)  I have replaced all four of the paddle jacks.  The jack in use switch is good in all 4 jacks.  Each of the 4 jacks can read the paddle potentiometer.

3)  The paddle sense line at the back of the jacks is VCC if any of the 4 jacks are unplugged, and is disconnected from VCC if all 4 paddles are plugged in.

4)  The signal from the right b jack is present at pin 13 of the pong chip, and I can correctly read the resistance value from there.

5)  I changed out the chip with one from a water damaged console, and I get exactly the same problem with the other chip.

6)  The 68nF cap hanging off the Right B line tests as 71 nF, which is within spec.



The circuit is really simple, and I am out of ideas.  Does anyone have any suggestions?

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  • 2 weeks later...

I have done more research, on it, and it is really weird.  With everything turned off, the paddle resistance reads properly in the circuit.  When I apply power, the paddle line is stuck at a high voltage.  I would guess it is a problem in the pong chip,  but I have two of them and they both do the same thing.  Has anybody else seen this failure mode?



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