Supergun PSU earthing woes

[Nimmers]

Hey all,

Looking for some advice on an issue that is driving me crazy. It will take a bit of explaining so bear with me.

I recently got a Vega 9000DX. It is much the same as the one depicted here. It's awesome but one day the power supply died and I could not find the exact replacement for the Sanwa swn-7e so I replaced it with a very similar one I found here.


Now when I replaced the power supply, being Australian and a licensed Electrician (which I haven't done for a living for 18 years now), when I looked inside I noticed the Japanese don't earth things. I figured what the hell, I will replace the power lead with a standard 3 pin Australian plug and connect earth to the case with a lug and connect the frame ground on the power supply. I did it for 2 reasons: 240v straight into a metal box like this is actually illegal here and I have small children in the house who I don't want to be electrocuted.



Anyway it all works fine except for one little issue: When the AC powerleads are near one another I get a slight diagonal shimmering on the screen - its very slight but noticeable. I can't capture it well on a camera I am connected via RGB to my monitor.

• If I disconnect the new earth wire the problem goes away but I am back to my original issue of mains power un-earthed in a metal box.
• I read in a couple of places that some arcade operators connect the logic ground to the frame ground because these issues stem from a ground loop issue - this sounds to me like a terrible idea.
• I tried to use a ferrite bead around my power cable which didn't help.
• If I separate the AC leads from one another, even by like half a meter or so the issue goes away.
• I thought I could maybe wire in an EMI filter but it looks like my power supply already has one internally.

I obviously can fix this pretty simply by just keeping the power cords physically apart from one another but I would love to hear from someone who might know why this is happening or who might know how I can fix it.

Cheers!

 

[deibit]

when I looked inside I noticed the Japanese don't earth things

Of course they don't, their island is so tiny that it would be physically imposible for their earth to absorb all the necessary grounding energy for all available electrical devices in Japan...

( )

ps- They ground, not necessarily through the plug, but usually there's a ground post on the wall, next to the standard electrical plug, the ground is then connected directly from the device (metal chassis of the PSU for example) to the post, or to a ground distributor in case several machines are involved (for example at the arcade)

 

[twistedsymphony]

have you tried using an AC line filter? it seems just about every arcade machine I've worked on has one

FWIW my Japanese DDR cab, Net City and Egret 29 were all wired properly with an earth ground from the factory. including the PSU, monitor etc. However both the E29 and DDR cab had it disconnected by someone along the way.

i have noticed some Japanese PSUs don't provide a pin for the earth ground but rather tie the wire directly to the metal cage (the SUN PSUs for NAOMI are like this as are the Peter Chou PSUs used in Model 2 setups and the original Taito PSU in my E29)... maybe that's how your original Sanwa PSU was designed to be used?

 

[Asayuki]

Hey all,

Looking for some advice on an issue that is driving me crazy. It will take a bit of explaining so bear with me.

I recently got a Vega 9000DX. It is much the same as the one depicted here. It's awesome but one day the power supply died and I could not find the exact replacement for the Sanwa swn-7e so I replaced it with a very similar one I found here.


Now when I replaced the power supply, being Australian and a licensed Electrician (which I haven't done for a living for 18 years now), when I looked inside I noticed the Japanese don't earth things. I figured what the hell, I will replace the power lead with a standard 3 pin Australian plug and connect earth to the case with a lug and connect the frame ground on the power supply. I did it for 2 reasons: 240v straight into a metal box like this is actually illegal here and I have small children in the house who I don't want to be electrocuted.



Anyway it all works fine except for one little issue: When the AC powerleads are near one another I get a slight diagonal shimmering on the screen - its very slight but noticeable. I can't capture it well on a camera I am connected via RGB to my monitor.

• If I disconnect the new earth wire the problem goes away but I am back to my original issue of mains power un-earthed in a metal box.
• I read in a couple of places that some arcade operators connect the logic ground to the frame ground because these issues stem from a ground loop issue - this sounds to me like a terrible idea.
• I tried to use a ferrite bead around my power cable which didn't help.
• If I separate the AC leads from one another, even by like half a meter or so the issue goes away.
• I thought I could maybe wire in an EMI filter but it looks like my power supply already has one internally.

I obviously can fix this pretty simply by just keeping the power cords physically apart from one another but I would love to hear from someone who might know why this is happening or who might know how I can fix it.

Cheers!

You absolutely do have a ground loop around. But the problem is not the loop itself; it rather is the way the grounding is routed. Too close to a strong AC source (mains trafo, crt joke, lopt, etc. etc.) and you get exactly the disturbance you are talking about.
Relocating the cables might solve the problem without having to add filters, ferrites, and other expensive jigs that are typically used for EMI issues. One thing you also might want to do is to ensure that the video signal to the monitor gets its ground "only" from the board (by making sure the video ground runs together with the RGBs wires and the overall length of the video connection is by far shorter than the chassis ground).

 

[skate323k137]

Just connect earth to DC com on the psu with a jumper wire. It'll clear it up. Done it a million times. I thought it sounded crazy too, but my PSUs that dont suffer this problem make that connection internally anyway.

 

[Nimmers]

Just connect earth to DC com on the psu with a jumper wire. It'll clear it up. Done it a million times. I thought it sounded crazy too, but my PSUs that dont suffer this problem make that connection internally anyway.

Just gave this a try and it did fix it.

Took my multimeter to investigate and I found this:

Common on Jamma Harness > Common on my RGBS BNC connectors > PVM metal chassis > Vega chassis via the earths in the wall socket.

So it seems that the common on BNC connectors for video inputs on a Sony PVM is connected to earth. Also tested on a couple of other PVMs I have and they are the same.

I guess in this case there is no harm in leaving the jumper connected because under normal operation its still bridged, albeit by the scenic route.

Just fired up a couple of games and they look crystal clear now. Thanks all for your advice and input!