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Guest LiqMat

Color adjustment on the VIC-20

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Guest LiqMat

So I finally restored an old VIC-20 back to life and shined it up. This particular one looked like it had been stored 6ft underground. It was filthy, but she looks great now and has a new 32K memory expansion on her plus IC Diamond thermal compound on the metal heatsinks to replace the dried up 35 year old compound that was there. I have it hooked up to composite and everything looks and runs good (except the power switch, which is sticky and I am replacing soon), but I have noticed the color is slightly off compared to the emu I run. Popeye 2015 title screen for instance. On the emu Popeye's face is the proper beige(ish) skin color, but when I run it on my restored VIC-20 his face is light pink. I played with the video pots (I have the model with two pots) and black level seems to do nothing with the composite signal and video level just brightens it up a bit, but the color stays. Any ideas on this? Thanks. Maybe the video chip is slightly off? I have another VIC-20 I may swap the MOS out on.

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Are you using an NTSC VIC-20? In that case light orange might actually look like light pink. I have both a PAL and NTSC VIC20, both modded for S-Video output. You can find comparison-videos of both here:

 

http://www.tokra.de/vic/colourtest/

 

I've recorded these directly with a hard-disk-recorder of the S-Video cables from the VIC. As you will see light orange looks pinkish for me on NTSC as well, I don't think there is a solution for this.

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Guest LiqMat

Spot on! There it is. Yes NTSC. PAL is more accurate in color it seems. Weird thing is on the emu, Popeye title screen looks correct tone on both PAL and NTSC setting. I suppose on the real hardware is where the difference is noticed. Thanks for the info and the video.

Edited by LiqMat

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Guest LiqMat

To fine tune the colors on the VIC20 read this article on Denials's wiki:

 

http://sleepingelephant.com/denial/wiki/index.php?title=Video_signal_adjustments

 

This wont help the actual color. I have the older VIC-20 with two pots and all you can adjust is black level and video level, but not color (hue). Tokra's post explains exactly the problem. The NTSC machine I have produces a light pink for what should be light orange and his video shows PAL producing a proper light orange compared to NTSC. No big deal, but the Popeye title screen looks proper color on a real hardware PAL machine. Play Tokra's two videos side by side and you will see the difference.

Edited by LiqMat

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Guest LiqMat

Are you using an NTSC VIC-20? In that case light orange might actually look like light pink. I have both a PAL and NTSC VIC20, both modded for S-Video output. You can find comparison-videos of both here:

 

http://www.tokra.de/vic/colourtest/

 

I've recorded these directly with a hard-disk-recorder of the S-Video cables from the VIC. As you will see light orange looks pinkish for me on NTSC as well, I don't think there is a solution for this.

 

So I finally got to the other early model VIC-20 which has a slightly different variant 6560 and guess what? The colors are correct on that one like in your PAL video even though it's another NTSC unit. I guess it varies per machine. Weird. So in the title screen of Popeye 2015 his face is pink (improper light orange) on one VIC and flesh tone (proper light orange) on another. The pots of course have no effect on the color issue.

Edited by LiqMat

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Interesting! Do the VICs have different power supplies? Mine with the pinkish orange has a DIN-plug (like a C64). What do yours have? The older model just has a 2-pin-plug.

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Guest LiqMat

Interesting! Do the VICs have different power supplies? Mine with the pinkish orange has a DIN-plug (like a C64). What do yours have? The older model just has a 2-pin-plug.

 

Yes. Both my VICS are the older bronze color case badge with the two prong power and internal heat sinks. They display color differently though. I did read a thread over at the Denial VIC-20 forums on the S-Video mod for the VIC-20 that they found Commodore would tinker with the traces and circuitry on the same model. Maybe refine it. I noticed my 6560 in one looks slightly different than the other so maybe all 6560s are not made the same. I did notice on the VIC that has the proper color also has much worse vertical banding on screen so I may do a cap mod that I read about over at Denial to reduce that. I am not going to do the S-Video mod since none of my screens support S-Video. The VIC that has the pink instead of light orange has almost no vertical banding on screen, but does have a bit of pixel jump on the edges of some graphics.

 

http://sleepingelephant.com/ipw-web/bulletin/bb/viewtopic.php?f=11&t=2477

Edited by LiqMat

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To fine tune the colors on the VIC20 read this article on Denials's wiki:

 

http://sleepingelephant.com/denial/wiki/index.php?title=Video_signal_adjustments

The article states, "The device labelled as C55 (or C48 for cost reduced board) is a fine tuning adjustment for the TTL clock driving the 6560 chip and should not be altered."

 

I have found that this is exactly what needs to be altered in order to fix colors that are slightly off. Some VIC-20's boot up with a green border instead of cyan. Fine tuning the frequency will correct this. For some VIC's the variable capacitor (C55 or C48) must be adjusted with a non-conductive alignment tool. Using a metal tool, like a jewelers screwdriver, will often interfere with the color signal making it impossible to see the colors while adjusting. It would probably be a good idea to use some form of thread lock (Loctite) to paint on once it has been properly adjusted.

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