Coleco Acting Up After Warmed Up

[nick3092]

I have a ColecoVision console that I recapped a while back (within the past year). I don't play it much, if ever to. E honest. But tonight decided I wanted to. However, tonight it's exhibiting a very odd behavior. I can sit here and play a single game no problem for 2-15 minutes. But as soon as I turn it off and put in a new game, when it powers back on, I have 45 degree lines all across the screen.

 

But, if I turn it off for around 30-45 seconds, then power it on, everything is fine again.

 

Leads me to believe it's some kind of heat related issue. But, I can seem to play a single game fine indefinitely, and the issue only occurs when I turn it off and back on again in short order (less than a minute) that I have problems. Which doesnt make sense that it is a heat related issue, as the problem should show up while I'm playing a game for several minutes. But it doesn't until I turn it off and on again, even if the game I was playing was for only a few minutes.

 

I have a second console, and while it has its own issues (the RF jack seems to have a bad solder joint, as I have to wiggle the same RG6 cable around to get a good signal), it does not exhibit the same issue with 45 degree lines after warming up and changing games.

 

That to me means the power transformer is good, as is the RG6 and the second console (except for when you wiggle the RF cable). So that means something odd is going on with the first console. But it doesn't make sense if it's heat related why I can play a game for over 10 minutes with no issue. But as soon as I swap carts, I have to wait to power it on again. Until I let it cool for 30 seconds or so.

 

The power switch has been cleaned with deoxit. But I don't think it's the culprit based on the behavior. The console was also AV modded, but shouldn't matter as I'm ramming the RF signal into my tv via quad shield RG6.

 

Any ideas?

 

Thanks,

 

-Nick

[nick3092]

So more info. This is really strange. The issue does not exhibit at all through the A/V mod. And while it's happening through RF, as soon as I hook up the video cable to the TV, it clears up immediately through RF. I can disconnect the video cable after it clears up, and the picture remains clear through RF until the next power cycle (assuming I don't let it cool down again).

 

This is the mod that is in my Coleco. https://www.a1k0n.net/projects/coleco/

[Bmack36]

If the video is fine through the AV mod, it is most likely the RF box. Try resoldering the output connector and the shield for the RF.

[nick3092]

I actually know the guy who designed the video amp. So I reached out him to get his thoughts. While he's great with electronics in general, he's self admittedly not very familiar with the "dark arts" of RF. But he thinks some oscillation is being inductively picked up. And it could be the video amp itself or something else on the board. He suggested shorting the composite jack, and sure enough it cleaned up the RF the same way as when I connected it to the TV.

 

I'm leaning towards the amp causing the interference somehow. He thinks the LM318 is self oscillating when there is no load on it. So I think the CV itself is probably fine. No one would probably notice, because apparently I'm the only guy who uses RF on a modded console. So I can either make a shorted plug for the composite jack, or use the composite signal.

Edited August 11, 2017 by nick3092