Weird interference issue

[ubersaurus]

I'm having a problem with my four switch 2600. After running a game for about 10 minutes, a rainbowy interference pattern starts to appear on screen and gets increasingly worse until I power cycle the system. It doesn't always appear, but often enough that it's an issue. I've got a link to a short video I took of the issue:

 

What could the issue be? Power supply? Voltage regulator? I took it to a shop, and they said they replaced the Mylar capacitor and the rf modulator. Not sure what else it could be.

[Rom Collector]

Are you using S cable, composite, or RF? In your video, it looks like composite.

If "the shop" said "they replaced the Mylar capacitor and the RF modulator", and you are using composite, I'd say someones completely full of it.

First, the RF modulator wouldn't be an issue at all in most cases. Only perhaps if you are using RF.

Most likely its the main ELECTROLYTIC capacitor. Mylar caps dont usually go bad. They can, but its MUCH more likely with an electrolytic cap.

So, usually its best to replace the largest electrolytic first, then work your way smaller till the problem goes away. Or replace all the electrolytics, but leave the other components alone.

I know this first hand, as I sometimes repair old radios, or other audio equipment.

KJ6JJK

[ubersaurus]

Are you using S cable, composite, or RF? In your video, it looks like composite.

If "the shop" said "they replaced the Mylar capacitor and the RF modulator", and you are using composite, I'd say someones completely full of it.

First, the RF modulator wouldn't be an issue at all in most cases. Only perhaps if you are using RF.

Most likely its the main ELECTROLYTIC capacitor. Mylar caps dont usually go bad. They can, but its MUCH more likely with an electrolytic cap.

So, usually its best to replace the largest electrolytic first, then work your way smaller till the problem goes away. Or replace all the electrolytics, but leave the other components alone.

I know this first hand, as I sometimes repair old radios, or other audio equipment.

KJ6JJK

This is through RF, not composite (it's just a really nice signal).

 

I did touch base with Best Electronics and he suggested it could be a bad power supply, power jack, or voltage regulator (and the service manual adds an inductor ferrite bead as a possible culprit). Two different power supplies saw the same issue so I doubt that's it, and the shop reportedly found all the electrolytic caps are in good shape (they were last time I checked it as well).

[Rom Collector]

I still think its the main electrolytic cap. (The biggest one) Or one of the other electrolytics.

2nd guess would be the voltage regulator.

If the shop you took it to cant figure it out, I would have someone else look at it.

I'm sure GameTechUS https://www.youtube.com/channel/UCyUGc-ZrN4JSox9Kbvnxeugcould figure it out. He's not the fastest or cheapest, but I have more confidence in him, than just about anyone else.

[ubersaurus]

My last update on this was that even after replacing the voltage regulator - the usual culprit - the interference issue is still emerging about 15 minutes on the dot after a power up. The tech's been on vacation since, but reportedly plans on swapping the ICs on the board to see if any of them are the problem (assuming it is heat-related and not electrical). I suppose it is possible given that one of them suffered a bit of corrosion damage on a leg from the console sitting in storage (though the chip itself looked fine) but yeah, no idea. I'll double check with the guy when he's back in town on the capacitors, though.

 

Your GameTechUS fellow seems to no longer be taking new repair jobs.

[Rom Collector]

I'm sorry the GameTechUS fellow is no longer available.

I'll bet you $s to doughnuts its not an IC.

I'm sticking to my electrolytic capacitor theory.

[texpat]

My 4 switch was losing color and getting a wavy thumbprint interference about 5 - 10 minutes after starting playing.

 

Changing the Mylar 0.1 uF C241 fixed it. I just needed a hot soldering iron and some solder braid to desolder and it was easy to refit a new one. I used a 0.1 uF 50v but it should be 100v.

[mojoatomic]

It's not an IC; replace C243 (2200uf 16v or higher v rating) and C241 (.1uf 100v mylar, even if there's a ceramic disk in there) and the issue will go away. Replace C214 & C243 since your in there anyway (4.7uf 35v or better).

 

​You simply cannot judge the health of a capacitor by it's appearance, although I wish you could :-) Electrolytics only have a useful (in spec) lifespan of around 10 years. The .1uf mylar cap breaks down from ripple current - that's part of it's job.

Edited February 1, 2017 by mojoatomic

[+-^CrossBow^-]

Pick up one of these kits...I've used several and it has helped in many cases with clearing up poor picture and audio.

 

https://console5.com/store/atari-2600-total-refresh-kit-new-capacitors.html

 

Having said that, I've also had two 2600s that I fixed that while they didn't do anything like what is in the video at the top of the thread, they did start to color shift on the graphics after a while. Ended up being the TIA's on both of those. Old style grey colored chips...

[ubersaurus]

The shop I took it to replaced the Mylar cap near the voltage regulator to no avail, but reported today that after swapping the ICs and voltage regulator the problem has cleared up! Wouldn't shock me if the Tia was having a problem.

[Keatah]

The power off = immediate fix is more akin to a leaky semiconductor. It's too easy to always go for caps.

[Omega-TI]

My suggestion would be to get some component cooler and apply to any suspect component and see if there is a change due to thermal variance. Do not rule out discrete transistors if you have one in the display circuit, that could also be a possibility.