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Colecovision composite mod degrading?

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I have a Colecovision with a mod for composite that I installed a couple of years ago. I think I bought the mod on ebay. Lately I am noticing some red bars on the screen. Is this a common failure? What should I check?

 

 

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If this is using the old Ben Heck mod, I had a problem with mine not too long after I had installed it. Basically the transistor essentially burned up due to the +12 applied to it and no where to sink that heat. Not saying that is the same here, but I was happy to switch it out with one of the other kits later on.

 

 

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On 9/17/2021 at 8:49 AM, -^CrossBow^- said:

If this is using the old Ben Heck mod, I had a problem with mine not too long after I had installed it. Basically the transistor essentially burned up due to the +12 applied to it and no where to sink that heat. Not saying that is the same here, but I was happy to switch it out with one of the other kits later on.

 

 

So the Ben heck mod isn't good long term? Crap. That's the one I was going to do for composite. 

 

Any suggestions for straight composite mod?

 

I'd like to know the method the OPs coleco uses.

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There are several kits you can get for colecovision composite that are based on the newer circuits that work better longer term. I've got a Retrofixes one in my personal CV along with the TMS-RGB and I've installed several others will all of them giving similar results.

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On 10/3/2021 at 5:21 PM, Dopy25 said:

So the Ben heck mod isn't good long term? Crap. That's the one I was going to do for composite. 

 

Any suggestions for straight composite mod?

 

I'd like to know the method the OPs coleco uses.

The biggest problem with the Heck mod is that it does not have the 75-ohm series output resistor.  So the composite output is going straight through the transistor at full amperage to the TV.  There is no current limiting at all on that path.  So yeah it overworks the transistor.  I bet if Ben took a fresh look at this mod today he'd either delete it or fix it (likely with a TV output amplifier instead of a simple emitter follower circuit).

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1 hour ago, ChildOfCv said:

The biggest problem with the Heck mod is that it does not have the 75-ohm series output resistor.  So the composite output is going straight through the transistor at full amperage to the TV.  There is no current limiting at all on that path.  So yeah it overworks the transistor.  I bet if Ben took a fresh look at this mod today he'd either delete it or fix it (likely with a TV output amplifier instead of a simple emitter follower circuit).

Awesome. A few days ago I found a forum member posted a project on oshpark. I ordered the minimum of 3 and will order the lm318 when I get my controller IC from digikey. Sounds like it will be the best way to go.

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