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Blast City grounding issue

nassekova

nassekova

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Long story short, between my Blast CIty JAMMA ground, and cabinet ground (cables screwed to the floor) goes 170V AC live, and I would like to fix this.

This whole thing started with MiSTercade remote, since I always got small electric shocks from the remotes metal casing when I touched it and some metal screws from my control panel.

As you can see there is ~170V AC going on between those two, so no wonder :D
IMG_6275.jpeg


At first I thought that perhaps this is a MiSTercade issue (some more troubleshooting there), but soon enough I found out, that my JAMMA edge ground is not the same as the cabinet floor ground. And not just that but between those two, I have 170V AC going on ?(

So this ground here at the bottom of my cabinet, which also is connected to my control panels metal plate.
IMG_6285.jpeg


And my JAMMA ground
IMG_6286.jpeg



There is live/hot 170AC between those two (when cabinet is on) and no continuity between.

I have changed the JAMMA edge on this one, so could I have fucked it up and put wrong cables on the ground in there or something? And since this is 100v Japanese cabinet, 170V must come from the CRT chassis side right? Any ideas how to start troubleshooting this or where the issue could most likely be?


Everything on the cable management side seems to be in order as far as you can eyeball it.
IMG_6281.jpeg
 
notsonic said:
Check for continuity between the control panel and the ground pin on the cabinet power cord.

Also check that there's no continuity between the monitor frame and the control panel.
Click to expand...

1. control panel and ground pin on the cabinet power cord HAS continuety
2. monitor frame and control panel DOES NO HAVE continuity.
 
DC ground =/= Earth ground. I would keep them separate.

Monitor should be floating. The metal bar below the monitor shouldn't be grounded IIRC.

What kind of stepdown were you using again?
 
The issue here is that the Mistercade remote is effectively using DC ground as shield ground, and it's shorting to your cabinet's earth ground. Sega cabinets don't tie earth to DC ground, or when they do it's through a capacitor.

Still, I'm surprised there's that much of a voltage potential. Can you post your stepdown transformer?
Is there continuity between the control panel ground and your house's ground?
 
notsonic said:
The issue here is that the Mistercade remote is effectively using DC ground as shield ground, and it's shorting to your cabinet's earth ground. Sega cabinets don't tie earth to DC ground, or when they do it's through a capacitor.

Still, I'm surprised there's that much of a voltage potential. Can you post your stepdown transformer?
Is there continuity between the control panel ground and your house's ground?
Click to expand...

I have this pretty beefy Stepdown and when I read it from the flat terminals it's about 100v
IMG_6291.jpeg


BUT when I connect the multimeter to ground and either of the flat terminals I get either 130v or 230v
IMG_6293.jpeg

IMG_6292.jpeg


And for the 2nd question, YES my control panel has continuity for my house ground.
 
I have no experience with anything not American, but 230v between neutral and ground seems like something isn't right with that transformer.
 
notsonic said:
I have no experience with anything not American, but 230v between neutral and ground seems like something isn't right with that transformer.
Click to expand...

I tried from my wall socket and with hot and ground I get 230V from there too. Only difference with the stepdown is that it gives 130V with neutral and ground where wall socket gives 0V. I have two of these stepdown transformers and both of these give that 130V with neutral and ground, so I guess thats just a "feature" on these. Or then my old house electrics are fucked up, I really don't know what I'm supposed to get from these :D

But I think the issue here is like you said:
notsonic said:
The issue here is that the Mistercade remote is effectively using DC ground as shield ground, and it's shorting to your cabinet's earth ground. Sega cabinets don't tie earth to DC ground, or when they do it's through a capacitor.
Click to expand...

Is there some safety risks if I just disconnect this ground cable from my control panel, so it won't be (earth) grounded and MiSTercades remote won't short with the screws?

IMG_6279.jpeg


Another solution would be to tape those screw heads but that would affect the aesthetics...
 
I don't think there's a lot of risk leaving the panel ungrounded. I almost never connect mine since I never made one for most of my harnesses.

I would prefer if some European users could chime in on the stepdown transformer behavior though.

Edit: is it possible you have live and neutral swapped on your transformer (or outlet)? Are Finnish outlets polarized? If not, you can try plugging it in the other way and measure the 120v outlet again.
 
Last edited:
I tried to plug it other way but there is no difference. Still get the same 230V and 130V from the ground and other socket. I have two of these stepdowns and both of them have the same issue. These were pretty expensive and made for Japanese Hi-fi ehnthusiastics. Might be some kind of designs flaw on the stepdown transformer side then :/ Or then it's my 1952 old house electrics that are not done by the book.

I think I will take the panel earth ground cable off and live with it for now. I have another isolating stepdown transformer, but it's 110V and has no ground socket at all, so this cable won't fit on that.
 
I just tested a 500W Airlink. On the output side I'm getting 0V between Neutral and Earth, 99V between Live and Earth, 99V between Live and Neutral. Which is what I expected.

However, I then tested a 1000W Erlong. On the output side I'm getting 78V between Neutral and Earth, 147V between Live and Earth, 101V between Live and Neutral.

Both transformers have a straight connection from Earth input to Earth output and the metal enclosure on the Airlink and the metal frame on the Erlong are grounded.

My mains outlet shows 225V between Live and Earth.

@nassekova, I think yours are working exactly as they should be.

Maybe get a plastic enclosure for the remote.
 
nem said:
I just tested a 500W Airlink. On the output side I'm getting 0V between Neutral and Earth, 99V between Live and Earth, 99V between Live and Neutral. Which is what I expected.

However, I then tested a 1000W Erlong. On the output side I'm getting 78V between Neutral and Earth, 147V between Live and Earth, 101V between Live and Neutral.

Both transformers have a straight connection from Earth input to Earth output and the metal enclosure on the Airlink and the metal frame on the Erlong are grounded.

My mains outlet shows 225V between Live and Earth.

@nassekova, I think yours are working exactly as they should be.

Maybe get a plastic enclosure for the remote.
Click to expand...

Yea I just disconnected the control panel earth ground cable and now there is no issues what so ever :thumbup:
IMG_6283.jpeg
 
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nem said:
No, because it's an isolating transformer. Doesn't matter which way you plug it in.

Are these Airlink ones?
Click to expand...

Surprise, Airlink step down transformers aren't isolating. I was reading the datasheet today.

They're autotransformers, so both the input and output share a common neutral and earth. That means that if neutral on the input side isn't at ground voltage, then the output isn't either.

Doesn't relate to this case, but something to keep in mind.
 
@nassekova I just stumpled over your post in the mistercade thread since i was reading through it.
You had a pic there where you measure between GND and LIVE, also you mentioned that you're livin in an old house.
This (old house) reminded me about the Nullung (German Word i'm missing the proper english word) where in the past there it was just a Bridge behind the sockets between N and PE!
This was called TNC (Terra Neutral Combiné) and was replaced by TNS (Terra Neutral Separé), where N and PE are separate wires.

It's been over 20 Years since my education as electrican, where i learnt that.

https://en.wikipedia.org/wiki/Bootleg_ground
This is the TNC ive talking about.

In the wiki page FI is mentioned! Maybe you got an old installation, i guess.
 
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