Composite-modded 4-switch CX2600A from Osgeld only displaying B&W - Help me diagnose!

[SpotAnime]

Hi Everyone:

 

I previously posted in this thread, but it was suggested we break this out to its own thread for folks with similar hardware and issues to reference going forward.

 

Back in April 2017 I purchased an NTSC composite-modded Woody 4-switch CX2600A from @Osgeld. It had been working great but was in storage for the past year unused (climate-controlled, dry finished basement in closed Rubbermaid storage container). I recently pulled it out after purchasing a Harmony cart for it, and when I hooked it back up it was not displaying color, only black and white. The black and white switch still works, as evidenced when playing Adventure and switching it I can see the grayscale changing.

 

Here's a picture of the composite mod, which Osgeld mentioned in the previous thread:

Quote

That board is just a video amp color is mixed onboard like normal

 

In the other thread, it was suggested I clean out and adjust the R213 pot which affects color. I used some electrical contact cleaner and adjusted it back and forth to free up any corrosion, but it did not fix the issue. I know it's getting voltage as I measured it, which I'll reference below. I also noted I can see some convergence going on when adjusting it either way, so it seems to be working as intended.

 

The good folks in the previous thread asked me to take some voltage measurements of the areas of the board responsible for the color signal, which I've copied here:

 

R213 - 6.22

R212 left side - 9.52

R212 right side - 6.23

TIA pins 9 and 20 - 5.02

TIA pin 10 - 4.66

 

I put in Asteroids, and yes voltage on pin 9 changed to 2.75. Turning the pot clockwise about a quarter turn increases voltage slightly to 2.82. Counter clockwise a half turn and it goes down to 1.81.

 

For Pin 10, turning the pot clockwise about a quarter turn increases to 5.95. Counter clockwise a half turn and it goes down to 0.35. 

 

I was also asked to measure the voltage along the traces for multiple resistors. For orientation, please reference the picture below:

 

^ Top; v Bottom

 

C210 "bottom" - 4.78
C210 "top" - 5.02
R210 "bottom" - 4.98
R210 "top" - 5.01
C211 "bottom" - 0.19 <- I wonder if this could be the problem?
C211 "top" - 4.98

 

R222 "bottom" - 0.19

R222 "top" - 0.00

C215 "bottom" - 0.19

C215 "top" - 0.00

 

Upon close inspection, C211 doesn't look to be a stock resistor (maybe part of the mod performed?) and might suffer from a cold solder joint as referenced by a poster in the other thread:

 

 

Or maybe those voltage readings are completely normal...I dunno.

 

Here are some other pictures of the circuit board and mod for reference:

 

 

 

 

 

 

The good folks @ChildOfCv, @DrVenkman, @fdr4prez and @-^CrossBow^- helped me get to where I am now, but I need some help to further diagnose this issue and identify a fix. Also, as I mentioned, this will be a good reference in the future for others with this mod setup.

 

TIA!

[AtariBrian]

Do you happen to know if your console here would let you use paddles? I also got one of his modded systems but noticed much later on that paddles would not work on his system...

[Shawn]

Could be the voltage regulator or the TIA chip.

[SpotAnime]

49 minutes ago, AtariBrian said:

Do you happen to know if your console here would let you use paddles? I also got one of his modded systems but noticed much later on that paddles would not work on his system...

I was able to use Paddles on it before, yes, so maybe just your console?

[SpotAnime]

39 minutes ago, Shawn said:

Could be the voltage regulator or the TIA chip.

Which is the voltage regulator? I think Best still sells TIA chips - that was my first inclination, to replace that. Since it's socketed it should be easy to pop in a new one.

[ChildOfCv]

2 hours ago, Shawn said:

Could be the voltage regulator or the TIA chip.

He's getting a solid 5V.  Also, the TIA chip does seem to be outputting color and reacting properly to the potentiometer.  The chip supply is dwindling, so replacing it on a whim is increasingly a bad idea.  Best is also becoming increasingly concerned that people decide they REALLY need a new TIA before buying one.

 

The best bet is likely to let someone with better test equipment examine the system.  A scope that "might" be useful for this task would run at least $80.  Most likely choice would be a USB scope for your computer.

[SpotAnime]

I've heard @Cmherndon79 does great mod work, so tagging him here. Does he also accept repair work like this? If I need to pay $80 for a scope to diagnose the problem, I might as well just pay that to someone who already has one and can repair it for me. BTW, other option is to buy one of their pre-modded consoles (it's ony $30 difference), but figured having a partially-functional console already would be the cheaper option.

[Osgeld]

sorry I have been sick (not the ronna but weirded out for a few days) I have been out of the atari modding scene for a couple years now but if you want to pay postage to me in TN (like ~9 10 bucks usps) I can trouble shoot and mail it back (though if its a TIA I am out of those with a vader sitting on the shelf waiting for one) 

[SpotAnime]

On 2/28/2021 at 12:18 AM, Osgeld said:

sorry I have been sick (not the ronna but weirded out for a few days) I have been out of the atari modding scene for a couple years now but if you want to pay postage to me in TN (like ~9 10 bucks usps) I can trouble shoot and mail it back (though if its a TIA I am out of those with a vader sitting on the shelf waiting for one) 

Hey not a problem and glad you are feeling better. Like I had mentioned in the previous thread, not looking for any sort of "warranty" so don't feel obligated, especially if you are busy with other things. I posted around other console repair forums/discords and I'm going to try to see if that solder joint on C211 is cold by resoldering it. If that doesn't do the trick, I'll let you know. Thanks for offering though! And if I do end up sending it to you, I'm paying you for the repair as I would any other modder, even for the diagnosis. If the TIA does need to be replaced, I have no problem getting a new modded console.

[SpotAnime]

Bumping this for a quick question. C211 is listed on the 2600 field service guide as a 22pF capacitor. If I were to replace this, will any 22pF capacitor do? Or is there a specific type I should be looking for?

[ChildOfCv]

Through-hole, MLCC capacitor.  Either radial or axial, doesn't matter.

[SpotAnime]

Necro-bumping this for a quick update.

 

I finally had some time to work on this today (as well as replacing the batteries on my three Dreamcasts with battery holders, yay!). I replaced the capacitor in C211 with this one to spec from Digikey. Good news and bad news:

 

The bad news first - still no color. When I power on the system, however I see a flicker of colored artifacts/lines on the side of the screen. I don't know if that's signal noise or an indicator of the issue. Everything else works great though - loads games fine, sound is great, and the composite mod Osgeld used is fantastic, as the picture is clear and there is no ghosting I've seen with other composite mods. 

 

The good news, is that I ruled out C211 as the culprit. And as I'm a beginner at soldering, I'm kinda proud I was able to swap them out and not cause any other issue. That I didn't introduce another problem is a win in my book lol.

 

 

[+wongojack]

Hey @SpotAnime did you or Os ever get this working?

[SpotAnime]

Nope. Was just thinking about this yesterday. I wish I knew more about how to triage this, and sounded like Osgeld was pretty busy with other things so I didn't want to bother him. Was kinda waiting for some other advice ot someone else who has the time to work on this. Was thinking of maybe sending to ITC. 

 

My luck it's a bad TIA and just needs a donor chip. 

[zylon]

On 2/24/2021 at 11:41 AM, AtariBrian said:

Do you happen to know if your console here would let you use paddles? I also got one of his modded systems but noticed much later on that paddles would not work on his system...

Paddles not working is classic on 4sw models. They do not have the hex buffer inline to protect the TIA

[zylon]

putting a small resistor across here warms up the 4sw color to that of a 6er, but not sure if it will bring back lost color.