Information wanted for Venture Line 6 Pac I Pong game

[JNP-3R]

Hey everybody. I'm curious if any of y'all have experience working on older arcade or pong games. I was recently contacted to help fix up what I believe is a 6 Pac I retrofit board by Venture Line that's integrated into a third party cabinet (Tennistronics?). The unit is old school. All 7400 logic, 555s for timing, and so on. No microprocessors in sight.

The unit's in surprisingly good condition, but has an issue with the 3rd player paddle. It seems that the paddle will always extend from the bottom of the screen to where it ought to be, it's about normal width if you move it to the bottom, or player 3 can move it to the top and just shut down all opposition with a great wall of paddle :3

I've tried some basic stuff like cleaning and reseating connectors (and that got the sound working!), but think this may be a dead logic chip or similar. I have some basic digital experience, and if I were to try to build a discrete pong unit I'd have a circuit that generates a window or threshold from the voltage on the paddle potentiometer, and then use a set of comparators to display the paddle on the right scan lines.

The issue is I don't know enough about arcade machines to know what other logical blocks to look for in the circuit or how to find the interesting bits without doing a complete reverse engineering to make a schematic and dig through it. Does anyone have any experience with these machines or, worst case, would know someone I can refer the repair to?

Attached are two pictures of the display so you can see the issue, an overview of the innards, and a pic of the table so you know what we're working on.

[stj]

interesting.
i'll do some digging.
if you look at the manuals for atari pong you may learn something, it has lots of descriptions of how everything works

[stj]

i think it's a clone/rip of Pong Doubles from ATARI.
https://www.youtube.com/watch?v=09qHnr1DMwA

your lucky, ATARI means full manuals and schematics - they included them in the machines they sold!
i'll look around for a set.
the reference for the game is :TM-014

[stj]

schematic - probably very similar

[JNP-3R]

Oh sweet! I figured it was its own thing since it has 6 pong variants (see the flyer: https://archive.org/details/arcadefl...pac-i_6-pac-ii), but with the generated display and construction looking so similar that should at least give me somewhere to start on the doubles mode. There's only so many ways to build a pong machine anyhow.

Thanks for digging!

[redwire]

It's like the original Space Invaders - no CPU, just a discrete logic state machine.
The board goes back to 1974-75 and I would automatically replace all the electrolytic capacitors and tantalums as well. Almost 50 years old...
I think the joystick A/D could be done with 555 timers so those caps would be replaced first.

[stj]

the 555's are fine, they create a variable frequency that drives a gated counter.

[R_J]

The same board is here, with some information, https://www.aussiearcade.com/topic/8...-repair-log-1/
Here is more info, but no schematic for the board only the monitor https://www.arcade-museum.com/C/Challenge.html

[JNP-3R]

Now that's some high quality information! Thanks!

Interestingly I had thought that the Venture Line upgrade was a whole set of new boards, but it looks like they just replaced a few components with sockets and piggybacked on to the original board, so that'll be a great resource.

[JNP-3R]

Oh, and if anyone else needs some digital review (like I did) to understand the circuit, here's a great writeup: http://www.pong-story.com/LAWN_TENNIS.pdf

It looks like the timing on the bat generators is controlled by the 555 timers. They seem to be running monostable to create a variable delay to generate the bat data at the right scanline if I'm understanding right. The timing capacitors are ceramic, but I may replace the filter caps next to them start investigating the ceramics in detail.

[JNP-3R]

Sorry it's been so long y'all. I've kinda had this on the back burner for a bit. I did get the recap done (and cleaned some liquid corrosion I'd missed earlier, d'oh!), but still no dice.

Did some digging and started to play with the board, and the bat generators are actually pretty different from the Atari ones. There's an LM339 being used to read the control pots that generates a PWM signal to represent their position. That's then used to gate pulses that feed into the rest of the circuit, and that's where it gets hard to keep track of short pulses whose patterns vary over long times with my basic oscilloscope.

Guessing this is a stuck gate or bad ceramic cap, but not sure how to narrow it down (other than a full reverse engineering) and I think I've gotten to the end of what I can help with. Anyone have any arcade repair contacts in the western US I can refer this to?

[stj]

there was a place that did old black&white stuff - i think it was called Electron Forge