Help needed-'83 Chexx sounds became distorted and crackle

[racki]

I recently purchased an '83 Chexx that played all the sounds perfectly.  However, once I turned the volume knob (which hadn't been touched in years) the sounds became badly distorted.   The volume doesn't change anymore when I turn the knob.  The ambient crowd sounds that play continuously throughout the game are completely gone, and all I hear in their place is loud crackling.  The other crowd sounds...(cheering / booing / ohh's) are still there but distorted.  The national anthem is also a bit distorted, but not as much as the crowd.  The keyboard player sounds are perfectly fine.   When I called I.C.E. they told me to replace the volume assembly, which I did.  It's made for a newer machine, so I had to splice the wires to the old logic board connector.  That didn't help at all.  The sounds are all the same, and the new volume knob still doesn't do anything to the volume level.  I'm not completely sure if the wiring is correct, because the 3 wires have different colors than the original.  Original was black, clear, and unwrapped wire.  The new one is black, black w/red stripe, black w/white stripe.  I figured black goes to black, but the other two I was unsure.  I ended up trying it both ways, neither worked.  Either way, I'm not sure volume has much to do with the sound distortion because it sounds the same when the volume assembly is unplugged from the logic board.  Now when I plug the assembly back in, the sound goes out completely.  (Before swapping the wires it still played the distored audio.)    One other thing to mention....with the volume assembly unplugged, I can sometimes faintly hear the organ music and other sounds from inside the cabinet, and they don't sound distorted, but they are almost inaudible.  At this point, I.C.E. wants me to send the board in, which I will if I have to, but that's a last resort.   I'd really appreciate advice from people on this board, who seem to know more about the original game than the company does.  

[racki]

update: I sent the board and scoreboard to I.C.E. They couldn't find anything wrong with it. They claim to have tested all the sounds. So now they say it must be the wiring or the speakers. But I don't see how that could be since the moog keyboard sounds play perfectly. I think that some of the ROM chips got fried when I adjusted the volume. I would like to pull the one causing the crowd static, but I'm afraid of damaging the working chips. Does anyone know which chips are related to which sounds? And is there anyway of finding replacement chips for an '83 chexx?

[rlsjr65]

Hi.

Have you been able to sort this out? I have a very similar problem. I bought the same game used and there was no sound at all. I noticed my volume control was burnt out and when I disconnected it I actually started getting sounds, but with similar quality issues as you. I replaced the volume control knob but when I hook it up the sound disappears again. I may have bought the wrong resistance on the knob and I stupidly tossed the old one. Any chance you know the correct resistance for the knob? I'm going to keep working on mine and will let you know if I figure anything out.

[racki]

I gave up on it for a while but I'm planning to get back to it soon.  I also threw out the old knob.  If you figure anything out let me know, I'll do the same. 

[lukerailey68]

1983 CPU Volume Control Knob is a 100K Ohm audio potentiometer.

There is some info on Chexx CPUs here.

Here are the wiring diagrams they provide: Part4, Part5, Part3..

I am still a novice with circuits but if you need help let me know.

[racki]

*SOLVED*  (after all these years)

After spending many hours on and off on this project, it turns out one of the internal volume wheels was malfunctioning.  I didn't think of this earlier because each speaker has an independent volume wheel, and both speakers had the same problem.  I also re-connected one of the green ground wires at the bottom of the circuit board because it wasn't making a clean contact.  Maybe that played a part, but I'm pretty sure the volume wheel was the fix.  I simply removed it, since ICE doesn't even sell those old ones anymore.  Everything works fine now, and I'm still using the 5k volume pot that ICE sells for Super Chexx.  It doesn't allow for much volume level adjusting, but it's at a good level and sounds perfectly clear, so I'll just leave it alone.  Hope this helps anyone having similar problems. 

[danimal]

What do mean by internal volume wheel?

[racki]

Inside the machine, mine had a small, flat disc near each speaker. The speaker wires connected to it. You could rotate the disc on the outer edge to adjust the volume of each speaker independently. I think mine had gone bad. They aren't necessary, so i just removed them from the wiring.