Colecovision problem

[retrocak]

I'm sure similar problems have been covered, but I need some guidance. My Colecovision boots up and plays fine. But after about 5-10 minutes, the screen starts bouncing and the screen edges zig-zag. It's very consistent. I have done a lot of cleaning, but it doesn't help. I've used my Atari expansion and had no problems. Any ideas? Thanks in advance.

[Ruggers Customs]

I'm sure similar problems have been covered, but I need some guidance. My Colecovision boots up and plays fine. But after about 5-10 minutes, the screen starts bouncing and the screen edges zig-zag. It's very consistent. I have done a lot of cleaning, but it doesn't help. I've used my Atari expansion and had no problems. Any ideas? Thanks in advance.

Hey Retrocak! It sounds like it might be a voltage issue which is generally where one would start trouble shooting anyways.

 

Use a multi meter and test the voltages of your power supply. If all your voltages are within spec, then open up your coleco and measure the voltages on the back of the jack with the power supply plugged into it. If your voltages are out of whack then it's possible that the connectors inside the power supply plug aren't making good contact with the pins inside the jack. Use something like a pic to try and bend them back to where they make better contact.

 

If your voltages are good then move onto your power switch. Purchase some CRC Contact cleaner (available from walmart, home depot, lowes or any hardware store or autoparts store. Generally runs about 6 bucks for a decent sized can.) Spray the switch well while switching it off and on to get the gunk out of there.

 

If these simple voltage checks and services don't solve your problem then it's an issue somewhere further up the chain and could be something simple as a bad cap or it could be a faulty ram chip.

 

Good luck!

[HOME AUTOMATION]

Have you checked if semiconductors are overheating, if any parts use heat sink grease... old dried out grease does not transfer the heat away efficiently.

[+-^CrossBow^-]

Was going to say, he states it comes up fine and plays fine, just after so much time it starts to exhibit issues. That is a heat related issue for sure. My first guess is something up with the video IC. Faulty ram in my experience will pretty much always give you graphic issues from the get go and usually the graphic glitching from faulty ram will always be the same pattern. So say you have certain patterns glitching in Donkey Kong, the exact same graphic glitching would happen if there is a ram module as in the exact patterns.

 

Also most Colecovisions have a heatsink on the video processor. However, one of mine never had a heatsink on it and it has been fine over the years. It doesn't show evidence that it ever had a heatsink on it either so I'm wondering if there was a later revision of CVs that didn't require the heatsink on the VDP?