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Diagonal video noise issue

msamiullah

msamiullah

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I am having diagonal video noise (floating) on all of the boards I connect to. I am using HAS V5 with Meanwell RT65A connected to Commodore 1084 monitor. When I replace the Meanwell RT65A with ITE switching power supply the diagonal video noise completely goes away which suggests there is something wrong with my RT65A. This is how I have wired-up RT65A.
Any suggestions?

1753328657560.jpeg
 
Im thinking ground loop interference. sometimes happens when both the monitor and the power supply are both earthed and that loop acts like a giant antenna. I;m not familiar with the 1084, dont know if its earthed or not, but that would be my first thought.

If you want to check you could temporarily lift the ground pin on either the power supply or the monitor - an unearthed device with a metal chassis isn't super safe, but any electrical device without an RCD/GFCI isn't super safe anyway

For a more permanent fix an isolation transformer would do it, or more exotic like this https://k.kramerav.com/downloads/pdf/product/1/OC-4.pdf
 
hatmoose said:
Im thinking ground loop interference. sometimes happens when both the monitor and the power supply are both earthed and that loop acts like a giant antenna. I;m not familiar with the 1084, dont know if its earthed or not, but that would be my first thought.

If you want to check you could temporarily lift the ground pin on either the power supply or the monitor - an unearthed device with a metal chassis isn't super safe, but any electrical device without an RCD/GFCI isn't super safe anyway

For a more permanent fix an isolation transformer would do it, or more exotic like this https://k.kramerav.com/downloads/pdf/product/1/OC-4.pdf
Click to expand...
Thanks, I havnt tested it yet but it looks like ground looping issue becuase the ITE power supply that gives clean video (no video noise) has only two prongs on the connector side.
streetfighterken said:
Bridge COM to Earth Ground.
Click to expand...
Is it safe to do? I searched it online and pretty much everywhere its mentioned not to do it.
 
msamiullah said:
Is it safe to do? I searched it online and pretty much everywhere its mentioned not to do it.
Click to expand...

There are multiple threads here (and possibly on AO from what I remember) telling people to do exactly this with Mean Well PSUs.

Out of curiosity, could you link to examples of people saying not to do it? What's the argument against it?
 
Interesting. ChatGPT seems to have a slightly different opinion (see attached).

I am far from an expert, but there's more than a few instances of hobbyists and operators doing this without incident. I meant to try it myself to try and solve an intermittent issue I was seeing after installing a Mean Well in an older cab, but never got around to it. I do think GPT's suggestion of putting a resistor/cap in-line is... interesting, but, again not an expert.

My take? Just bridge 'em.
 

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msamiullah said:
just a follow on up on this, I bridged COM and Earth Ground and it completely resolved the video noise issue (thank you), Picture now is as pristine as it gets:
1753743141108.jpeg
Click to expand...
I had similar problems when I used very cheap PSUs with my Superguns
It's been a while I believe I was running my Atomiswave on a VGA CRT Monitor and I'd have to bridge COM and Earth to get rid of the video noise with those cheap PSUs

I ended replacing those cheap PSUs out for Meanwells without having to do the bridging trick
 
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