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VIC-20 cycling green band visible in border

D

Divarin

Veteran Member
Joined
Mar 9, 2019
Messages
610
Location
Cleveland, OH
Here is a video of what I'm seeing (it's much more noticeable in real life the camera isn't quite capturing it right):

Any idea what could cause this? I have already adjusted the brightness pot (it was very dark). I also tried the other two pots just to see what would happen but didn't have any affect on this issue.
 
Looks very much like mains hum is causing it. Have you tried the monitor on a different signal source? Have you tried a different monitor on your VIC?
If it turns out that it is the VIC and not the monitor, you will need to look at the power supply circuitry. What version VIC do you have? Is it one with a DIN connector for power, or does it have a 2 pin socket that takes 9V AC from the power brick?
 
A4000Bear said:
Looks very much like mains hum is causing it. Have you tried the monitor on a different signal source? Have you tried a different monitor on your VIC?
If it turns out that it is the VIC and not the monitor, you will need to look at the power supply circuitry. What version VIC do you have? Is it one with a DIN connector for power, or does it have a 2 pin socket that takes 9V AC from the power brick?
Click to expand...
Two pin socket one. I just picked this VIC-20 up and it didn't have a power supply so I made one using a 9v AC power supply that I had lying around and soldering on a 2 pin connector. It could be that particular power supply is a little noisy. I can try something different. The monitor is fine I use it for lots of other stuff but I'll start by trying a different power supply.
 
Okay different power supply same issue. I then moved the computer into another room and hooked it up to my 1702 monitor it's still doing the same thing but looks a bit different: instead of being mostly cyan with a green band running through it's mostly green with a (less noticeable) cyan band running through. Although a slight adjustment to the tint on the 1702 makes the border cyan and the green band almost invisible.
 
Divarin said:
Two pin socket one. I just picked this VIC-20 up and it didn't have a power supply so I made one using a 9v AC power supply that I had lying around and soldering on a 2 pin connector. It could be that particular power supply is a little noisy. I can try something different. The monitor is fine I use it for lots of other stuff but I'll start by trying a different power supply.
Click to expand...
That type VIC requires 9V AC at 3 A. If your transformer has an insufficient current rating, you may find the voltage may drop below 9V, causing the power supply in the VIC to drop out of regulation, causing hum. Your video showing the wavy video confirms you have a hum problem.

If your transformer can provide 9V at 3 A, then you have a problem with the power supply inside the VIC. Check that C59 (4,700uF, 16V) is good. Other things to check are the bridge rectifier, voltage regulator, and C44.
 
A4000Bear said:
That type VIC requires 9V AC at 3 A. If your transformer has an insufficient current rating, you may find the voltage may drop below 9V, causing the power supply in the VIC to drop out of regulation, causing hum. Your video showing the wavy video confirms you have a hum problem.

If your transformer can provide 9V at 3 A, then you have a problem with the power supply inside the VIC. Check that C59 (4,700uF, 16V) is good. Other things to check are the bridge rectifier, voltage regulator, and C44.
Click to expand...

Thanks I have another thread on this topic and the folks on that thread came to the same conclusion.
 
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