VCS color fades

[+SpiceWare]

I've been having an issue lately with the color fading out of the signal on my Atari. I also sometimes see some color fringing that I hadn't seen before.

 

Any pointers on what to check for?

[cwilkson]

I would suspect a power supply issue. Bunch of questions....

 

Which deck is it? Is it stock RF, or is it A/V modded? (and which mod?) Which type of output are you using? And what type of TV?

 

What's plugged into the cart and joystick ports? What the rating of your power brick? (probably 9V, either 300mA or 500mA)

 

Does it happen repeatedly? (in-out-in-out...) Does it happen immediately on power up, or does it take a while? Is it game dependent?

 

If you have a voltmeter, measure the voltage across the big electrolytic cap on the motherboard. And measure the output of the 7805 +5V regulator.

The middle pin is ground. Measure from there to the other 2 pins. Pin 3 should be very close to 5V. Pin 1 is the same as the electrolytic cap - should be 7V at a bare minimum but 8V or more is better.

 

Do the measurements with nothing plugged in and the deck turned on. Then repeat it after adding a cart and controllers.

[cwilkson]

I would suspect a power supply issue. Bunch of questions....

 

Which deck is it? Is it stock RF, or is it A/V modded? (and which mod?) Which type of output are you using? And what type of TV?

 

What's plugged into the cart and joystick ports? What the rating of your power brick? (probably 9V, either 300mA or 500mA)

 

Does it happen repeatedly? (in-out-in-out...) Does it happen immediately on power up, or does it take a while? Is it game dependent?

 

If you have a voltmeter, measure the voltage across the big electrolytic cap on the motherboard. And measure the output of the 7805 +5V regulator.

The middle pin is ground. Measure from there to the other 2 pins. Pin 3 should be very close to 5V. Pin 1 is the same as the electrolytic cap - should be 7V at a bare minimum but 8V or more is better.

 

Do the measurements with nothing plugged in and the deck turned on. Then repeat it after adding a cart and controllers.

[+SpiceWare]

It's a light sixer with your CyberTech driving a C= 1084S. My Amiga CD32 doesn't fade, so I know it's a problem with the Atari. Both are hooked up via an s-video switch box. Between the switchbox and C= monitor I have a professionally made cable that splits S-Video to 2 RCA.

 

I don't always notice it, so it could be related to the game and/or controller. Most recently I noticed it when running a test kernel for this year's Holiday Cart via my Krok Cart. It seems to take a little bit before it happens, though it's not consistent as to how quickly it occurs. When it occurs it repeatedly fades to grey, then back to color. Thinking back, I also noticed when we played Ikari Warriors for the HSC - which I had to play via the Krok Cart.

 

The power adaptor is a 9V 500mA that I'd picked up from Fry's a few years back. It's not a "selectable output", only the 9V 500mA and the price sticker actually referred to Atari.

 

I have a voltmeter, but need to track it down as my study's a mess after Ike. I'd been more concerned with getting the roof and fence repaired, and now that those are done cleaning up the study and replacing the desk are next to be addressed. I'll look for it today and post results as soon as I can.

 

Thanks!

Edited October 26, 2008 by SpiceWare

[+SpiceWare]

Readings w/out a cartridge or controller plugged in:

 

cap = 9.97

1-2 = 9.82

2-3 = 4.97

 

with Krok Cart and joystick

 

cap = 9.10

1-2 = 8.87

2-3 = 4.96

 

I tested the power adaptor as well and get 14.54v on it. Not sure why it's so much higher than 9, though testing another adaptor yielded similar results.

 

The colors are not fading at the moment, even after having left it running for a half hour. I'll leave the case apart and the voltmeter handy so I can take readings right away next time it starts acting up.

[cwilkson]

Hmm. Those voltages seem fine. So checking while the color is faded would be the next test. But if it happens "after a while" something is probably overheating, in the Atari or on the video card. If the voltages are ok while color is faded try checking the temperature of all the chips on the CyberTech card, including the TIA. I expect that one to be warm (hot?) and all the others to be cool during normal operation. Repeat the temperature checks when the color has faded. To help calibrate your finger, test a room temperature metal object before and after each chip. And remember to ground your finger first by touching the negative lead of the electrolytic cap on the motherboard just before touching a chip. Another thing to check is to take the switch and y/c splitter cable out of the signal path when the color fade is present. Maybe difficult with a 1084s. Try with a different monitor if you can. Those things are 20 years old and the electrolytics can be drying out. I've seen some issues with mine. Which version of the CyberTech board do you have? Does it have the adjustment pots? Does it have composite output? Is the board L-shaped?

 

Regarding 14V vs 9V coming out of the brick...any voltage source can be modeled as an ideal source with a resistor in series. The ideal source voltage is equal to the measured output voltage with no load connected. But when current is drawn by a load, the measured voltage will drop due to the loss in the series resistor. A brick that's rated at 9V, 500mA means that when you draw 500mA from it the voltage will drop to 9V (down from whatever the open circuit voltage is).

 

As an example, assume the console without peripherals draws 500mA (a fictitious but plausible number). A 14.5V unloaded output and a 10V output when loaded means the output resistance of your brick is causing a 4.5V loss. 4.5V/500mA = 9 Ohms ---> not very ideal!

[+SpiceWare]

I've opened it up and took a picture of the CyberTech so you can see which one it is. I have the Atari powered up and will let it run for a while again to see if it color fades so I can check the other things.

 

I have a C= 1084 (mono) I can try it out with as well.

[cwilkson]

Ok, you have the L-shaped board. There's no direct composite output from that one. But you do have the Saturation adjustment pot - the one on the left.

That might be something to play with the next time it's acting up. But try to do the voltage checks and temperature checks first. It would also be good to hot swap your monitor. While the color is faded, move the y/c cables from the 1084s to the 1084. If it's faded on both that (probably) rules out the monitor. If the 1084 doesn't show faded colors, switch back to the 1084s to make sure it's still showing fading.

[+SpiceWare]

Figures - now that I've brought it up, it hasn't occurred in over a week

[cwilkson]

That's a good thing!