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Atari 2600 jr. color problem


Dennis90

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I have a Junior console that's acting weird, the color gradually changes by itself when turned on and after a little while goes black & white. When you turn the console off and directly back on again, the color may come back, but just a few seconds. Then if you wait a while and turn it back on again, the colors will probably stay on a bit longer, but yeah, then gradually change and go black & white again like before. The Color/B&W switch works fine, and I replaced the big electrolytic capacitor, the four small 4.7uf electrolytic capacitors and the voltage regulator with new ones but I still have the same problem. I also replaced the color adjustment pot taken from another console, but that did not change anything either. So not sure what to do now, is there any other capacitors i should try change or something that can cause this problem? Can some of the non electrolytic ones cause this problem perhaps? It's AV modded with a transistor and 2x resistors btw. Hope someone can help!

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  • 1 month later...

I have not been able to fix this console yet. I also noticed that when you turn on the console without having it plugged in, the LED turns off very quickly, it does not seem to hold any charge, other jr. consoles I have seem to hold the charge much longer, it takes a few seconds for the LED to gradually turn off, but this console does it very quickly in comparison. Seems kinda weird since I changed the electrolytic capacitors.

I also have problem with another junior console, everything works perfectly, except the image is quite dark and ugly looking, any idea what can be the problem here? It's also AV modded.

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Color changing is also a possible indication that the TIA chip is failing or that the power current isn't optimal.

 

Did you do the AV mods on these or did you get them that way? Most of the dark looking image issues I've seen with the simple composite mod is due to the additional 75R added between the composite output signal and ground. This was needed on CRTs, but I've found it seems to produce a very dark image on more modern day displays and removing that will likely help. If it is present that is. I've seen them installed on the actual RCA output jacks and also seem them added directly on the composite amp board on the output pads.

 

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Hm, the AC adapter I use is fine tho at least, but could there still be a problem with the power current? And I have tried different TIA chips, and it did not seem to help.

I did the AV mods myself. And you mean the 75R is part of the mod? If so, I did not use one. And I only have CRTs, the image is dark and weird on 2 of my CRTs I tested with. Here is a photo of what it looks like:20201202_2212222.thumb.jpg.2fec6eff8a5dc599a471d031f71fa480.jpg

And you can also see it looks kinda weird in those places I drew circles around, adjusting the color pot does not take that away.

And I first tried this mod on both of these consoles: Transitor-mod-watermark.thumb.jpg.ba197bb2666c1138d41f840be68e35e5.jpg

And then I thought maybe another mod might work better since I got video problems, so I found this one and tried it on both consoles: https://www.console-corner.de/videomod.html

But that other mod did not change anything really, maybe the image looked slightly different, but yeah, still got the same video problems.

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1 hour ago, Dennis90 said:

I measured it and on one side it was 5,something volts, slightly decreasing all the time, and on the other side, it was 1,something volts, slightly increasing all the time, so it does not seem stable I guess? If I measured it correctly. I measured it like this:

 

To be clear; I know nothing about the internals of the '2600.

BUT, having said that -- when measuring voltages, I'd put the ground lead on an absolute guaranteed ground on the circuit, and then the other lead on the area I want to measure the voltage of.  That's just me... I'm a novice at electronics.

 

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Yeah, though the side connections across the wheel are the wiper, so at least there was a common point.  Apparently it's about 6V total, with either 1V or 5V depending on which side was actual ground.  Looking at the PCB traces, the 5V seems correct.  Makes sense, since they make sure to have more than 5V to the pot in the first place, which indicates that at least 5V should normally be required.

 

But measuring all voltages with the black probe on one of those bare strip areas such as where the RF shielding goes through would be best.

 

So, how much did the voltage change between color vs B/W?

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I tested some more now. I measured the voltage between the upper "orange" leg in my photo, and a big ground area, and it seems to be the same voltage as when I measure it between both of those "orange" legs, so that did not make any difference. But when i measured between the upper "green" leg and a big ground area, the voltage was the same as on the "orange" side, but I guess that is normal? And I also measured with the B/W switch off, that did not make any difference.

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4 hours ago, Dennis90 said:

I tested some more now. I measured the voltage between the upper "orange" leg in my photo, and a big ground area, and it seems to be the same voltage as when I measure it between both of those "orange" legs, so that did not make any difference. But when i measured between the upper "green" leg and a big ground area, the voltage was the same as on the "orange" side, but I guess that is normal? And I also measured with the B/W switch off, that did not make any difference.

Both of the upper parts, both the green and the orange, are the same connection, so that makes sense.  What's the measurement between the big ground area and the lower green?

 

The B/W switch shouldn't matter, oddly enough.  The switch is just another input for programs to read and react accordingly, if they care to.  It could just as easily be used as a difficulty modifier if the program chose to.  It does not directly affect the color generation.

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So it's the same even when the color fades out?

 

Okay, next check pin 9 of the TIA.  It should be more than zero but less than 5V.  When the color fades, if it reads at either extreme, then it can only be the TIA.

Are your chips socketed?  That's one potential problem, at least on old sockets, especially of the cheap single-wipe variety.  It could be that the socket needs to be replaced.  Temperature changes are a great way for a questionable contact to break continuity.

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