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Monitor Ground Loop Interference?

Hackcell said:
well, not all monitors use earth ground. MS8/MS9 monitors inside sega cabs are not grounded in any way.
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Yeah I clarified that in a followup post because I realized it could be read wrong. Inside a cab, the monitor is and should be floating. Lots of consumer TVs are floating as well (with most conductive stuff well shielded from casual touching). The problem arises because equipment like an extron with lots of exposed BNC ports is not and should not be floating, and it's made to connect to other stuff that is designed the same way.
 
yoooooon said:
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
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It is he. Hi pal.
 
dos said:
Yeah I clarified that in a followup post because I realized it could be read wrong. Inside a cab, the monitor is and should be floating. Lots of consumer TVs are floating as well (with most conductive stuff well shielded from casual touching). The problem arises because equipment like an extron with lots of exposed BNC ports is not and should not be floating, and it's made to connect to other stuff that is designed the same way.
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Sorry for reviving this old thread, but just a question about the floating ground. What would happen if I connect the floating ground of the cab to the common ground pin in the back of the cabinet?

I have a Mister FPGA in my cab and when measuring between the exposed metal of the MisterFpga and common ground in the back of the cab I see about 45v. The mister is connected to the internal floating ground by being connected to the PSU via JVS power (it's a sega new net city cab).

I have a second cab, same as the other, a New Net City, when I connected a NeoGeo MVS to JVS like the Mister also saw the same 45v between the NeoGeo and the ground point in the cab.
When I replaced the NeoGeo with a windows PC that isn't connected via the JVS PSU power, but instead connected directly with its own normal ATX PSU to the wall outlet, the difference measured between the pc and ground in the cab was now instead 0v. I suspect it's because the floating ground inside the cab is now grounded via the USB, VGA and RCA connector of the pc to the ATX PSU to the wall outlet.

I suspect I could connect a ground wire from the MisterFpga to the ground point in the cab but that would connect the whole floating ground as well to the ground point and I'm not sure what the safety problem could come with that. If it would be smart , I suspect Sega had done it from factory.
 
The monitor should be floating, the outside of the Net City should be grounded. Any connected hardware you can choose to ground as you see fit.

So why wouldn't you ground everything? It's because often the conductive hardware enclosure is also tied to common (DC) ground. I don't own a MiSTer, but my guess is when you tie the MiSTer case to Earth ground, you also tie common ground to Earth ground. This may or may not result in interference.

Normally arcade hardware is left ungrounded. The PCB tray is made out of wood for a reason.

However, there's no harm in experimenting. If you feel better that the metal case is at ground potential, then go for it.
 
nem said:
The monitor should be floating, the outside of the Net City should be grounded. Any connected hardware you can choose to ground as you see fit.

So why wouldn't you ground everything? It's because often the conductive hardware enclosure is also tied to common (DC) ground. I don't own a MiSTer, but my guess is when you tie the MiSTer case to Earth ground, you also tie common ground to Earth ground. This may or may not result in interference.

Normally arcade hardware is left ungrounded. The PCB tray is made out of wood for a reason.

However, there's no harm in experimenting. If you feel better that the metal case is at ground potential, then go for it.
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Thanx! Where is the potential difference between the floating ground and earth ground coming from? Sorry for a extremely newb question, unfortunately very blank on electronics, electric circuits and how they are designed and why, just trying to understand where the difference is coming from to avoid destroying stuff.
 
I have what looks like ghosting on a set of linked NACs. I recapped both PSUs, added ferrite chokes to both ends of the TOPs versus harness and made sure monitor is ungrounded. Swapped chassis on both sides as well, but still persists.

Also have this to some extent on my linked New Versus City cabinets (PFX).

All AC cords are original and running through a Tripp-lite Isoguard (isolated grounds) surge strip. Kind of stumped at this stage on the cause.
 
I'm going to try to run my cabinet of a UPS to disconnect it from the building grid to see if I get the same leaking current in my cabs when running isolated from the building out of curiosity to see what happens.
 
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