(Topic ID: 284752)

Unusual grounding issue in Williams System 11 PinBot

By MoSeS_1592

3 years ago


Topic Heartbeat

Topic Stats

You

Linked Games

No games have been linked to this topic.

    Topic Gallery

    View topic image gallery

    20210101_234522 (resized).jpg

    #1 3 years ago

    Last night I noticed by accident that if I, with a very light tough, I dragged my finger across the metal side rails on my PinBot I could feel a very subtle tingle. I only felt it when I would *move* my finger across the metal and it was barely noticeable. I was standing barefoot on my basement floor when I noticed it. First thing I did was placed a socket tester in the service outlet and it showed that the machine was properly grounded (at least at the outlet). Next thing I tried was a continuity test of the side rails to the rest of the machine and that checked out. Next thing I tried was a continuity test to the side rail of the machine I have next to PinBot, since both machines obviously share common ground. Funny thing is that the continuity tester chirped and pulsed in a pattern almost identical to a typical digital alarm clock alarm. Almost like continuity was 'almost there' for 3/4-second, then not present for 3/4-second, then present again, repeating. I then checked A/C voltage between PinBot's side rails and the grounded side rails on the adjacent machine. Oddly I got a reading of around 50V AC. I used a wire to short PinBot's side rails to the adjacent machines grounded side rails and nothing out of the ordinary happened except the 'tingle' went away when touching the metal while the wire shorted the rails.

    Any idea's why this is happening? Is this simply a sign of some place in the machine where the ground strap perhaps has some electrical resistance from a loose wing nut or dirt/corrosion/rust?

    #2 3 years ago

    What's the condition of the electrical cord plug? Grounding pin still in place?

    #3 3 years ago

    Probably your ground connection is bad. The 50V and slight tingle you feel are present because the game line filter has small capacitors from live and neutral to ground, and they act as voltage divider for your 110V line voltage. Not dangerous as such (very small current), but try to find out why the ground is not "grounded".

    #5 3 years ago

    Thanks for the replies! I will check ground plug and look at the linked article and report back.

    #6 3 years ago

    Well I figured out the problem. My machine really wasn't grounded at all. The grounding wire from the power cord was going to the service outlet and was grounded fine there. I checked continuity from the service outlet input ground prong hole to a known good ground source and it worked. I also checked continuity between ground in the steel plate box around the service outlet to a known good ground source and it worked. Then I noticed that there is no green wire ground coming from that box output to any of the ground braids anywhere in the machine and none of the ground braids are connected to this box. I checked continuity between all the braids and the side rails and plates in the machine and everything is well connected but none of this is connected to the actual ground. Furthermore there are only hot and neutral wires coming out of the the service outlet box with the fuse. No ground. Really strange. I wonder why somebody would have disconnected the ground from the rest of the machine? If I'm not supposed to see the green ground wire coming out of this hole in the photo then where exactly it is supposed to go to?

    20210101_234522 (resized).jpg20210101_234522 (resized).jpg
    #7 3 years ago

    Just checked my system 11 Bad Cats and Elvira, and they are both wired exactly like that. Everything inside is connected together by the ground strap, but the strap itself is not connected to mains ground.

    Maybe that's why nearly all Finnish games have an isolating transformer installed.

    WPC games seem to have their ground strap connected to mains ground however.

    #8 3 years ago

    I had this problem quite a bit when helping put together about 60 pins at a location. On EM's many plugs were not polarized or incorrectly polarized at the end of the zip cord. All non polarized plugs were replaced with polarized with wide blade being neutral. On SS games typically the problem was, again a switched neutral/hot when the previous owner replaced the factory molded plug and installed it incorrectly. On quite a few games, the molded factory plug seemed to have a break in the ground wire right where the wire exits the plug. And, on some, the ground was just cut off! In the end, every game was checked to make sure they were all on the same page. And yup, I got 50v also, after correcting the switched hot/neutral I got near 0v.

    #9 3 years ago

    Im confused. So the green ground wire from the the actual plug cord goes into (and is connected to) the service outlet box. The service outlet box is only connected to the rest of the machine by hot and neutral wires going to the transformer. Why the heck wouldn't the grounding straps be directly connected to the mains ground???

    To correct the issue I jumpered the metal service outlet box (which is directly connected to main ground) to a grounding strap. Is this ok? That fixed it, no shock, and side rails have continuity with external ground source.

    #10 3 years ago

    That is how WPC games do it, and perfectly OK if you have a properly grounded outlet and correct plug wiring.

    #11 3 years ago

    Is there any potential harm in jumpering the ground strap directly to ground like I've done?

    Reply

    Wanna join the discussion? Please sign in to reply to this topic.

    Hey there! Welcome to Pinside!

    Donate to Pinside

    Great to see you're enjoying Pinside! Did you know Pinside is able to run without any 3rd-party banners or ads, thanks to the support from our visitors? Please consider a donation to Pinside and get anext to your username to show for it! Or better yet, subscribe to Pinside+!


    This page was printed from https://pinside.com/pinball/forum/topic/unusual-grounding-issue-in-williams-system-11-pinbot and we tried optimising it for printing. Some page elements may have been deliberately hidden.

    Scan the QR code on the left to jump to the URL this document was printed from.