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Monitor Ground Loop Interference?

kikaso

kikaso

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So I'm having what I believe to be ground loop video interference in my arcade cabinet setup.

When connected to my NAOMI, I have what looks to be video interference in the form of horizontal banding. Here, I have the brightness turned down to highlight the banding.

NAOMI interference.jpg


I'm attaching a diagram of my current setup showing where ground lines go. But first, a few notes:

1. DC and field/earth ground terminals on my PSU are linked as per the cabinet's wiring diagram. Without the link, there's vertical video interference on Neo Geo one-slot and other boards I have tested.
2. Two-prong power cable was replaced a long time ago with a three-prong grounded cable.
3. Horizontal banding is only (most?) visible using NAOMI and not on other arcade boards, (tested MVS single slot and CPS2 and no horizontal banding).
4. Cabinet is all metal frame, (Mini Cute). Not sure if that matters.
5. I don't hear any of the audio hum associated with ground loops.
6. I have lots of ferrite beads on the JVS and JAMMA power harnesses and also the audio and video lines.
7. Both the Capcom IO board and NAOMI share the same PSU—the Mean Well QP-150 which has the 3.3V JVS requires in addition to 5/12/-5V for JAMMA.
8. Monitor chassis, NAOMI, and Capcom IO have all been re-capped.

Mini Cute Ground Loop copy.jpg


Given I'm only seeing the interference on the NAOMI, I suspect the ground loop may be here:

Mini Cute Ground Loop NAOMI.jpg


I also thought ground loop may be between monitor-field ground-PSU-IO but all of my other boards work fine with this same setup.

Any thoughts on where I should be looking? Is this even related to a ground loop? Thanks!

UPDATE: I disconnected the ground of the AC/mains power cable—no change.
I unlinked the DC and field/earth grounds of the PSU—no change.
I confirmed proper voltage on the 3.3 and 5V lines.
 
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THCsoftcore said:
Did you ever solve this?
Click to expand...
Nope

I replaced the power harness on the NAOMI with UL1007 rated wiring and I think it helped but the horizontal banding is still visible. I connected same setup to it Sony PVM and the banding was less but still visible on lower brightness. I have also since gotten rid of the Capcom IO in favor of a MultiJVS and the banding is still visible but barely noticeable during gameplay. Maybe I’m just getting used to it?

Since the only constant is the NAOMI and netdimm, I think the issue must be there somewhere.

Are you having similar issue?
 
THCsoftcore said:
Yes, similar issue but on supergun with the Meanwell PSU everyone recommends. Tempted to bridge DC ground to Earth.
Click to expand...
Check impedence between them 1st, on my Happ PSU's there was no continuity and bridging fixed this kind of stuff. However the meanwells I have already have those connections bridged / common internally, so no change would be expected in that case.
 
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do you have anything else plugged into the same circuit that could be causing interference?
i had some similar interference once... tried adjusting all sorts of shit. turns out the culprit was a completely separate neon sign plugged into the same outlet circuit. once i unplugged it, the interference went away...
there's probably a better explanation and/or solution but may be worth looking into.

also... are you the artist formerly known as thchardcore? lol
 
Inside a cab all power supplies are behind a isolation transformer, thus NO PSU should be connected to earth ground PERIOD (I don't give a shit what the manual/manufacture says).
The DC grounds of any/all PSU's should be bridged/jointed together, however DC grounds NEVER get mixed with earth ground... NEVER!

TkVvtDz.png


  • Purple = Isolation Transformer (should sit on feet/wood to keep electrically isolated from body/Earth Ground)
  • Red = PSU #1 JVS (should sit on feet/wood to keep electrically isolated from body/Earth Ground)
  • Red = PSU #2 Cab (should sit on feet/wood to keep electrically isolated from body/Earth Ground)
  • Blue = DC ground tired between PSUs
  • Gray = AC Line
  • Black = AC Neutral
  • Green = Earth Ground (connected to cab body and nothing else/isolated from transformer and PSUs)
 
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My issue was the fucking Extron 203. It seems to introduce a ground loop when used even if on a conditioner and all power cables far from video. PSU already replaced. I will try an isolation transformer or swap it with an older 202.
 
jassin000 said:
Yup ISOLATION TRANSFORMER.
Click to expand...
Pretty sure that's the 18v transformer for the sound amp. Unless you mean the line filter. See https://www.arcade-projects.com/threads/sega-sound-amp-specs.5273/

The monitors in my Sega cabs are powered from the mains, and Also, WG D9200's don't use ISO transformers either.

And yea, it's fine and you should earth ground the power supply powering your JAMMA etc equipment, as well as any other exposed metal, especially the CPs in candy cabs. If your monitor DOES use an isolation transformer then yeah of course by design it shouldn't be earthed.
 
Yeah I've been inside the PSUs of my Astro and Aero, no isolation transformer. Also both cabs have multiple factory earth grounds to things like the control panel and other internal/external metal surfaces the user or op is likely to touch. Never, ever heard that you're not supposed to have things grounded in a cab. I had to tie the outer case of my Aero's PSU to ground otherwise I'd get a huge shock off it.

My MVS-U4 just uses a generic screw terminal arcade power supply (no iso in these either). This is the type of power supply in question that sometimes causes ground loop interference to the CRT which is resolved by tying the FG and DC GND posts to each other. It is a well known technique (right or wrong) with arcade ops and you will find it done all day long in cabs with screw terminal PSUs. These type of PSUs sometimes even tie them together internally, you can check the continuity for yourself.
 
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jassin000 said:
How is this device earthed?
I suspect internally it might connect earth to case and IF the METAL BNC connectors are touching this METAL case...
The BNC's RGB-video/DC ground just made contact with case earth (that shouldn't happen).

Don't own one, never seen one in real life, just a guess.
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Dude most professional video equipment is designed this way on purpose including the extron. With all respect you're not giving good or safe (to humans or equipment) advice/info here. If removing earth ground from your video equipment clears up interference, then the problem is the wiring where you're at, not the fact that the equipment is properly grounded. I'm really not trying to start a flame war so don't take it the wrong way but it's just not something that should spread.

EDIT: In ham radio, it's common that they make their own ground spike and tie their stuff to that because the equipment is so sensitive to interference. It's still properly grounded, just not off the one built into their houses. Interference from grounding is common, but the solution isn't to disconnect the equipment entirely from ground.
 
One thing that is the case is that cab monitors are typically not grounded to earth. Even if there is no separate iso, the chassis themselves typically isolate the power section and only take hot and neutral (this is not the case for cab PSUs!). In this case, tying the monitor frame to earth ground would cause interference.

I suspect the interference from the extron was caused by this type of mismatch. Typically it is plugged into something like a PVM which is also sharing the earth ground. But my problem was only with the suggestion that it is some sort of wrong design on the part of the extron, and this:

NO PSU should be connected to earth ground PERIOD (I don't give a shit what the manual/manufacture says).

Green = Earth Ground (connected to cab body and nothing else/isolated from transformer and PSUs)
Click to expand...
 
dos said:
Dude most professional video equipment is designed this way on purpose including the extron. With all respect you're not giving good or safe (to humans or equipment) advice/info here. If removing earth ground from your video equipment clears up interference, then the problem is the wiring where you're at, not the fact that the equipment is properly grounded. I'm really not trying to start a flame war so don't take it the wrong way but it's just not something that should spread.

EDIT: In ham radio, it's common that they make their own ground spike and tie their stuff to that because the equipment is so sensitive to interference. It's still properly grounded, just not off the one built into their houses. Interference from grounding is common, but the solution isn't to disconnect the equipment entirely from ground.
Click to expand...
well, not all monitors use earth ground. MS8/MS9 monitors inside sega cabs are not grounded in any way.
 
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