Colecovision craps out when warmed up

[Schenley]

I have a Colecovsion that works fine - for about 5 minutes or so. I just tested it out, and here's the situation.

As I said, it plays perfectly for about 5 minutes of being on. When it gets warm, the top of the screen gets distorted, and gradually the rest of the screen joins in. The distortion is similar to when a TV's horiz/vert is off (remember that??) There is no 'giberish' - it's a wavy distortion.

It just did that, and then I shut it off for 10 minutes and fired it back up with the same symptoms, so I'm guessing that it has something to do with getting warm?

It's not the power supply. I used to have a working CV on this same power supply. I have the case removed (not the metal cage, however), and nothing feels abnormally warm.

I have checked the knowledge base, but didn't see anything.

Any ideas?

[FABombjoy]

I had this same problem once - turned out to be the video processor (TMS9928A). The unit had been "serviced" at some point and the heat sink left off of that chip.

[Schenley]

I had this same problem once - turned out to be the video processor (TMS9928A). The unit had been "serviced" at some point and the heat sink left off of that chip.

So, can I just look for that, and add a heat sink if needed? If so, where would I get one?

[FABombjoy]

A functional Colecovision

[Schenley]

Ooh.


Anyway, here's the internals:


I believe the chip you're talking about already has the heat sink on it...

In the background is another unit that has giberish on the screen all the time... Hopefully I can somehow combine these two to get one working system.

[FABombjoy]

Indeed, that heatsinked chip is the one.

I was able to confirm it on my machine via freezing the chip (which would cause the image to become clear and stable) followed by heating (which would cause an almost immediate crash).

[Schenley]

Well, I just played around with it some more. I left the CV on for over an hour, but with the case and cage off and a household fan blowing over the motherboard. Sure enough, it plays fine. So, it's definitely a case of overheating.

Are there any other chips that need heat sinks? Is adding a small computer fan out of the question?

[FABombjoy]

I don't think this is too common of a problem - mine was understandable, and yours is the 1st that I've heard of. Replacing the heatsink with one that has more fins & applying fresh heatsink compound (or something like Arctic Silver) would probably cure the problems altogether. A fan would help but might be overkill.

[Goblin]

Might be worth picking up a can of freeze spray from Radio Shack or some other electronics parts store to confirm that's the problem.

Another trick if you don't have freeze spray is to take a can of compressed air and turn it upside down. When I was temp testing some designs at work and the stock room was out of freeze this is what we did.

[Schenley]

I don't think this is too common of a problem - mine was understandable, and yours is the 1st that I've heard of. Replacing the heatsink with one that has more fins & applying fresh heatsink compound (or something like Arctic Silver) would probably cure the problems altogether. A fan would help but might be overkill.

OK, I've definitely confirmed that this is the problem - thanks to a can of freeze.

How do I aquire a heatsink with more fins? (If you say from another Colecovision....) Also, how do I remove the heatsink to reapply the compound? Does it just pry off, or will that damage the chip?

Thanks again, guys!