Need help with video signal

[JoMa]

Hello everyone,

 

First of all:

I am new to this forum and to the Atari 2600. I'm not sure if this is the right way/place to ask this, so if not, please tell me.

 

I recently bought an Atari 2600 (darth vader) PAL console in untested condition. I got it to work mostly, the problems it had have mostly been solved except for one: There is interference in the video (RF) signal, which results in white dots moving around the screen in waves. (I have attached a video and an image of it)

Here is what I already tried:

 

-Use an NES (nintendo) RF switch instead of the built-in cable: introduced more static and the white dots remained.

-Disconnected the RF cable from the Atari's motherboard and tried it with an NES: worked perfectly fine, no static at all.

-Cleaned both connectors and the cable with some alcohol: Improved nothing.

-Finetuned the tv channel multiple times.

 

Important to mention is that the cable has been damaged and soldered back together by the previous owner, but since it worked fine with the NES i don't think this is the problem. My guess would be that there is something wrong with the big capacitor on the board or the RF modulator. It could also be due to the power adapter, it is one of those universal adapters on which you can set the voltage, I set it to 9V, I dont have an original one.

 

Any help or tips would be greatly apriciated.

 

MOV_0053.mp4

[+Stephen Moss]

I am by no means certain of the following it is just a suggestion but...

From the video it is difficult to tell, from the photo it looks like the dots may possibly be an intermittent loss of blanking on the flyback line (if it is a CRT display), as you say it is fine with the NES we can probably eliminate the display as the problem.

As the RF cable is damaged I would try a new one, I may be ok with the NES if the NES is outputting a stronger signal than the VCS which would be less prone interference/noise pick up resulting form the repaired cable.

 

If that does not solve issue the only way to know if the problem lies with the 2600's RF unit is to either replace it or add a composite mod and see if you get the same problem, if you do see the same problem from the composite output then the problem could be caused by either noise/glithes in the video generation of the stage of the 2600.

[JoMa]

Thanks man, I will try finding a new rf Cable and I will tell if it worked!

 

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[dphirschler]

"Sparkles" is usually a symptom of needing to replace the green chicklet caps.

 

Darryl

[+DrVenkman]

"Sparkles" is usually a symptom of needing to replace the green chicklet caps.

 

Darryl

 

This. My Vader was having the same issue until I replaced the chicklet cap near the voltage regulator.

[JoMa]

"Sparkles" is usually a symptom of needing to replace the green chicklet caps.

 

Darryl

The new rf Cable and some fresh solder arrives today, so if the cable doesnt help nothing, I will have to break out the soldering iron

Thanks for the tip!

 

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[JoMa]

I just noticed something! Is this wire even supposed to be there on the underside of the board? It connects the voltage regulator with the negative side of the big cilinder capacitor. The soldering work seems very unproffessional too. Should i remove it and see what it does?

 

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[JoMa]

 

This. My Vader was having the same issue until I replaced the chicklet cap near the voltage regulator.

Just got my replacement cable and it makes the distortion even worse somehow! So i'm keeping the original cable. So what to do next? replace the chicklet cap i guess... Any info on what voltage it is?

 

Thanks for the help so far everyone!

[dphirschler]

Search in this forum for Atari 2600 tuneup. There is info there... although the guy is no longer selling kits, you can find them on Ebay and other sites. Or you can just get the parts yourself.

 

Darryl

[+DrVenkman]

That wire looks like some kind of ground jumper. I am unfamiliar with PAL boards so I have no idea what it's doing there. As for the chicklet cap, the largest voltage anywhere in the system is the 9V or so brought in from the power adapter before the voltage regulator steps it down to 5V. And for that matter, voltage and temperature ratings for capacitors are basically maximums. Anything below that is okay. The caps are 0.1uF polyester film capacitors. They very inexpensive; I bought a lot of 100 from an eBay sell for under $3US shipped. For what it's worth, the ones I have are rated at 100V, waaaay more than necessary for the job.

[JoMa]

That wire looks like some kind of ground jumper. I am unfamiliar with PAL boards so I have no idea what it's doing there. As for the chicklet cap, the largest voltage anywhere in the system is the 9V or so brought in from the power adapter before the voltage regulator steps it down to 5V. And for that matter, voltage and temperature ratings for capacitors are basically maximums. Anything below that is okay. The caps are 0.1uF polyester film capacitors. They very inexpensive; I bought a lot of 100 from an eBay sell for under $3US shipped. For what it's worth, the ones I have are rated at 100V, waaaay more than necessary for the job.

I will try and get to an electronics component store and see if they have what I need. Will tell you how it went. As for the wire: Upon further inspection, it was soldered to the screw holding down the voltage regulator. I took a risk and removed it, the Atari still worked perfectly after that, so I guess someone put that wire there years ago trying to fix an issue. I'm just going to keep it removed as it doesnt make a difference anyways, or does it?

[JoMa]

I just replaced All the green chicklet caps and the big capacitor, and guess what? Nothing! [emoji58], i'm getting a bit tired of this console. Whats next to try? Replace the voltage regulator? Replace the small cap above the RF unit? Or perhaps do a composite mod? I dont know anymore...

Edit: Could it still be the cheap power supply I use, its one of those with interchangeable plugs. Perhaps it's the issue. Also, just noticed, when i touch the connector on the board while the system is running, the distortion gets worse. So my guess is still that the RF mod is the issue at this point.

Edited December 16, 2017 by JoMa

[JeremiahK]

I don't know if you are using a TV/antenna switchbox or not, but my NTSC system used to do exactly what yours is doing back when I still used the switchbox. I got one of these, and it solved everything. Alternately, you could do a composite mod if you wanted, as that would also avoid the switchbox.

 

If you're not using a switchbox, I would do the composite mod, since you suspect that the issue might be in the RF modulator.

Edited December 16, 2017 by JeremiahK

[JoMa]

I don't know if you are using a TV/antenna switchbox or not, but my NTSC system used to do exactly what yours is doing back when I still used the switchbox. I got one of these, and it solved everything. Alternately, you could do a composite mod if you wanted, as that would also avoid the switchbox.

 

If you're not using a switchbox, I would do the composite mod, since you suspect that the issue might be in the RF modulator.

No, I'm not using a switch box. The PAL consoles have a coax plug that comes out of the system that you plug directly into the tv. I will probably try a composite mod!

[JeremiahK]

Here is a PDF step-by-step guide that shows how to do it for each system: http://www.coolretroprojects.com/Atari_2600_AV_Mod_Installation_Guide.pdf

 

And of course there are plenty of videos on YouTube showing how to do it as well.

[JoMa]

Here is a PDF step-by-step guide that shows how to do it for each system: http://www.coolretroprojects.com/Atari_2600_AV_Mod_Installation_Guide.pdf

 

And of course there are plenty of videos on YouTube showing how to do it as well.

Thanks man! Found that guide already, i'm probably going to buy this kit: https://www.benl.ebay.be/itm/Atari-2600-7800-NEW-AV-Composite-Mod-Kit-Audio/152509029274?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

It has a guide as well, so I'll see. If I get my atari fixed, I will of course post it here!

[alex_79]

My "vader" console behaves just like that, but it is not my primary console and I never bothered to find a fix.

You might try using clip-on ferrite beads on the coax cable, to see if you can filter out the interferences.

Try different positions (e.g near the console or near the tv end of the cable), maybe even two of them, one at each end. They're quite cheap on ebay and might be worth a try before attempting the mod. The simple transistor composite mod seems to result in poor video quality on most 4 switch models (you'll find a lot of threads on the subject), so you might considered a more sofisticated mod if the ferrite beads don't solve the problem.

[dphirschler]

Still shocked the caps didn't fix it.

 

Darryl