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VIC 20 rainbow colors in border during warmup

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Hi everyone 

I have a new-to-me early model VIC 20 that has an odd characteristic during warmup (first min or two after power on).  The borders of the screen will show some rainbows that move up and down before slowly fading away. Screen colors look off to me (I remember the screen to be much brighter).  I had to replace U11 already to get the BASIC prompt (carts worked ok).  Video trim pots don't really help much and crystal tests ok.  Any thoughts on what to look at next?  Using an av cable to lcd.


During warmup (example... the rainbow lines move around) 




After warmup



Thank you for your help!


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Looks like the video output is turned down too low or you are using the wrong video output.


The VIC-20 has video "hi" and "lo" outputs. Have you tried the other one, or is your cable pre-made and wrong? The impedance is different.


Edited by R.Cade
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When I was checking the cable, I found it was on "lo" (pin 4).  I built a new av cable with higher quality components, still using pin 4 and it didn't help at all.  I swapped to pin 5 ("hi") and have no output at all now.  I guess lo is the way to go.


I'll patch up the rf box next to see if I get the same result there, just to take the cable out of the equation. 

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Hi hofster,

I tried tweaking the two a bit. Unfortunately, neither affected the colors at all.  The one on the left (video level control) just sort of sharpened the image (intensity,  maybe?), while the one on the right (black level control) just turned the screen black when I turned it up (which makes sense).  I didn't see any other things I could adjust except the crystal.

Thank you for the link.  Best writeup on those that I've seen!


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Try bringing down the colour setting on your TV by a lot, and increase brightness a bit. When I alternate between Atari 8-bit and VIC-20 on the same LCD screen, using the same composite video cable (because they share the same pinout), I find that I need to bring down the colour saturation a lot with the VIC and then bring it back up again when I switch to the Atari.


But yeah, you should use pins 2 (ground), 3 (audio), 4 (video low) for the video cable. I'm not even sure all VICs output something on pin 5, or what signal strength it then has.

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Did some experiments tonight...


Lcd monitor using rf with adjusted color and brightness as suggested by carlsson:





Couldn't get any "cyaner" than that...


Swapped to av with the same settings:


better border, but white was still wacky.


I broke out the crt and...



wow, colors look really good!


still have the original rainbows in the border until it warms up for about 60 seconds tho. 😮‍💨




getting closer!

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  • 2 weeks later...

I recently had a similar symptom, but mine didn't clear up as it warmed up - it would lock up completely.  I did a couple of troubleshooting things at once, but I believe it came down to one of the original MOS 245s because it fell apart as I was removing it to troubleshoot.  Once I put in a new one everything looked good.  I didn't really investigate how/if it could have been related, but the VIC's been stable ever since.

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