Williams Comet (Williams, 1985) Voltage in System 9 Grounding Strap

[PinballWizardryKazow]

Hey Folks, this is my first post here in the Forum and I hope it is well recieved. I have found a strange thing in my Comet machine. There is a voltage present in the grounding strap. I first noticed it when I brushed up against the open door of the machine while it was on and got a bit of a zap. It feels like DC voltage and is in the ballpark of 0.85-6.0 volts. I measured the voltage of the "leak" by putting my mulitmeter on a water pipe for the grounded side (-), and the grounding strap for the "hot"(+). There is voltage present even when the darned thing is turned off (but still plugged in). hmmmmmm.... Is this normal?
If not, what should I do? I was thinking perhaps a capacitor was leaking DC current through to the ground.....possible? Or entirely normal? Looking forward to reading the replies. Thanks, PinballWizardryKazow

 

[sleepy]

Welcome.
I'm not sure about the machine, but it could be that your location's AC power is providing what they call "Mechanical Ground" instead of true Earth Ground. Mechanical ground AC systems are usually provided through power step up transformers (to save on the electric bill) and the ground potential is only relative, not absolute as in Earth Ground.
If so, then you might want to follow up on why the Mechanical Ground system in use at your location is not providing 0 (zero) ground potential.

Check between the Wall AC Ground pin and the pipe, but make damn sure you know what you are doing. We don't want bad surprises, or serious injuries.

And yes, I've experienced this same shock at arcades when touching the lockbars/metal frames on two adjacent machines when each machine had a difference in ground potential. Probably due to design differences and transformer Mechanical Ground in use at the location in order to save on the electric bill.

You know, I would ask a repair shop about whether the machine should be strapped to Earth Ground, or would be damaged if you did that, but if it is recommended then I would install a switch to the Earth Ground so the power is not draining/running up a bill when the machine is not in use. The machine should not shock at any rate.

 

[sleepy]

Welcome.
I'm not sure about the machine, but it could be that your location's AC power is providing what they call "Mechanical Ground" instead of true Earth Ground. Mechanical ground AC systems are usually provided through power step up transformers (to save on the electric bill) and the ground potential is only relative, not absolute as in Earth Ground.
If so, then you might want to follow up on why the Mechanical Ground system in use at your location is not providing 0 (zero) ground potential.

Check between the Wall AC Ground pin and the pipe, but make damn sure you know what you are doing. We don't want bad surprises, or serious injuries.

And yes, I've experienced this same shock at arcades when touching the lockbars/metal frames on two adjacent machines when each machine had a difference in ground potential. Probably due to design differences and transformer Mechanical Ground in use at the location in order to save on the electric bill.

You know, I would ask a repair shop about whether the machine should be strapped to Earth Ground, or would be damaged if you did that, but if it is recommended then I would install a switch to the Earth Ground so the power is not draining/running up a bill when the machine is not in use. The machine should not shock at any rate.

 

[druadic]

Two posts again John! What shall we do with Sleepy? ROFL

PinballWizardryKazow, welcome to the PN forums. Make yourself at home! :)

Honestly I know nothing of what you're asking so I'll leave it up to the experts that know this stuff.

druadic

 

[sleepy]

Hey, I didn't do that!
I was playing my mp3 and thought everything was O.K.