Robotron sound question

TheBasement

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I have a Robotron which the sound would work upon startup. But after playing a game for a minute or 2, the sound would disappear. I put the probe on the power supply in the cab, and at the 7805 on the sound board. All voltages tested good. Hitting the sound test button on sound board produced the test sounds, even though the in-game no longer had sound. That meant good voltage and good amp. Turning off the game and back on again would again produce sound for a few minutes.

I pulled the board and suspecting the 6821 PIA I reflowed all the 6821 pins with a soldering iron and also reflowed the data line connector header pins. Instead of immediately testing (which I should have done), I pulled the sound board from my Joust and swapped ROMS. I put the joust sound board in the Robotron and the Robotron in the Joust. At this time both games are running with full sound for the last hour without cutting out.

Is it possible that the pins only needed to be reflowed, especially since it got sound for a few minutes before cutting out? Should I still replace the 6821 PIA, or do you think I am in the clear?
 
I'd hold off on the 6821 replacement until you have more evidence that it is bad.

I'm thinking bad power to the sound board or an intermittant EPROM connection caused its CPU to temporarily quit operating properly. You affected both by pulling the power connector and swapping the ROMs.

Even if +5 looks good when you test it, it might be dipping while playing, causing the CPU to go off to never-never-land. A flaky EPROM connection could do the same. Could be that shaking from playing the game is aggravating the issue. There's no watchdog on the sound CPU to reset it if this happens.

Pushing the test button caused an NMI which made the CPU jump to the test routine in ROM. The 6821 wasn't reset, which is what's making me think CPU issue. Unfortunately, once you are in the test routine, you can't get out without powering down or manually resetting the sound CPU, both of which also reset the 6821.

Did you try leaving it in test mode for a couple of minutes to see if sound went away? If you powered up for 2 minutes but didn't play, did you have sound for 2 minutes when you did start playing?

I had a similar issue in my Joust and it turned out that a bad EPROM socket caused some address lines to flake out, and the CPU would lock up. After replacing the socket, everything was fine. If yours now works fine, I'm guessing you cleaned some gunk of an EPROM pin or a power connector by swapping things out.

Sean
 
Is this THE Sean Riddle? Does this mean your page will be back up? or has it moved?
 
I agree you may have fixed the issue but it will be difficult to determine the problem when you do more than one thing at a time. It is unlikely that cleaning the ROMS would have fixed it. If your ROM was ad you shouldn't get any sounds. So it is more likely that pulling the connector and reflowing the header may have fixed the connection issue that was either heat or vibration related. It may have been the headers or it may have been the pulling the connector off and putting it back on may have cleaned the connection.

Moral: if you want to know what the problem was, do one thing at a time.

ken
 
Is this THE Sean Riddle? Does this mean your page will be back up? or has it moved?

I feel more like "the" than "THE"....

My site is currently up at www.seanriddle.com. I moved and had to change ISPs again, so I got my own domain. Not much new there; I need to take some time to update stuff. I've been crazy busy for a while.

Sean
 
It's great to see you around Sean. Your pages helped me debug one of my first Williams boards (well, at least my first Williams board as a collector).

Hope to see you hanging out here once in a while.

ken
 
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