Atari 2600 - Black and White only

[Amerika]

Hello!

 

I recently acquired an Atari 2600 4 switch "Woody" and I was told by the guy that the machine was stuck in Black & White mode. I didn't think much of this as I figured it would be an easy fix due to switch being stuck or faulty or the potentiometer being out of wack. Welp, I was wrong!

 

The switch is just fine and it does swap between what appears to be black & white mode and color as the image does change and the potentiometer doesn't do anything while in B&W mode. And speaking of the pot, adjusting it will modify the image but color is never seen. The image always stays black and white.

 

I then thought that it might just be the RF connection. I had already purchased an composite mod so I went ahead and installed it hoping that bypassing the RF connection would bring back color. Nope! The image is nice and clean but it's still only in black and white. I have also tried on multiple TV's (two CRT's and an LCD).

 

I tried searching google and this forum and I never found anything definitive. Is this a known issue with a specific fix or does anybody happen to have an idea of how I can track down the problem? I am fairly good at soldering and I can use a multimeter.

[Atari030]

I have exactly the same fault with a Jr. I'll be keeping an eye on this one.

 

I replaced the 4050, colour blend pot and the TIA. I also tried a different AV mod, same result. Tested the BW switch and it appears to be toggling the TIA happily. Next trick is to test resistors/caps on the output and see if any are under spec. What I did notice is that there is colour bleed around the white on screen, so it is a bit weird.

 

My mucking around might give you some ideas. Which AV mod did you use?

[Amerika]

I have exactly the same fault with a Jr. I'll be keeping an eye on this one.

 

I replaced the 4050, colour blend pot and the TIA. I also tried a different AV mod, same result. Tested the BW switch and it appears to be toggling the TIA happily. Next trick is to test resistors/caps on the output and see if any are under spec. What I did notice is that there is colour bleed around the white on screen, so it is a bit weird.

 

My mucking around might give you some ideas. Which AV mod did you use?

This is the mod that I used: https://www.ebay.com/itm/Atari-2600-7800-A-V-Composite-RCA-Audio-Video-Mod-Kit-NEW-amp-IMPROVED-KIT-1G-/311705759237?&_trksid=p2056016.l4276

 

Hopefully that was a good one to get. I couldn't find much that seemed accurate in regards to mods being good/bad so I sort of threw a dart. I also modded an 7800 with the same kit and it looks great besides a bit of vertical banding with some colors that I don't think I can get rid of (almost every video I've seen of a 7800 has something similar). I might make a post with video at some point in the future here for that topic though.

 

I would definitely appreciate the sharing of any results that you get as I wouldn't mind trying a few things to bring this 2600 back to where it should be. It would hurt to throw it in a closet

 

I thought about trying something basic like this little kit: https://www.ebay.com/itm/Atari-2600-CX2600A-4-SWITCH-TUNE-UP-PARTS-VOLTAGE-REGULATOR-1-Amp-CAPACITORS-/311645406414?_trksid=p5731.m3795 But I have a feeling that the issue isn't something basic.

[Atari030]

It might be, but I'd doubt it. I have had trouble with ST's that recapping has helped and for machines like that I'd say it is worth doing. But, for something as simple as a 2600 with only a couple of caps, I can't see it being that important. As long as the PSU is OK, you should be pretty right.

 

I tried both a resistor ladder and a similar setup to yours. Same B&W result.

 

https://www.thefuturewas8bit.com/index.php/2600_comp_mod

 

Same setup, by the looks of it.