Multiwilliams - Help me not electrocute someone please!

[saint]

I purchased a Defender cabinet that had been converted to a MultiWilliams a while back. The power cord had been altered to remove the grounding prong. When I went to replace it, I noticed a few things about the wiring that concern me.  A description of the wiring:

---. The power cord (sans ground) is wired into a Sprague Filter (http://arcadecontrols.com/temp/Multiwilliams/S_DSCN1349.JPG) on the three-wire side of the filter.  The two wires from the electrical cord go into the blue and brown wires. Nothing goes into the third (green) wire.  The two wires coming out of the other side of the filter go into a  junction block. That then connects to an isolation transformer (http://arcadecontrols.com/temp/Multiwilliams/S_DSCN1347.JPG) that looks kind of icky, on the side of the isolation transformer that has only two wires. The opposite side of the transformer has three wires.  Two of the three wires (blue and brown) go up to power the monitor. The third (yellow) goes nowhere.

Also coming out of the junction block that comes out of the Sprague Filter are two wires that run to a power supply (http://arcadecontrols.com/temp/Multiwilliams/S_DSCN1346.JPG) -- two black wires that lead to the 115V hookups. This power supply then feeds the PCB (http://arcadecontrols.com/temp/Multiwilliams/S_DSCN1350.JPG), and marquee light.

(In case that was confusing: Power_Cord--->Sprague_Filter--->Junction_Block.  Junction block splits the hot and neutral wires to both the isolation transformer and the power supply)

---. The metal braid that is normally used for grounding the monitor frame, coin door, etc... is not connected to anything that might ground it. It runs throughout the cabinet touching the monitor frame, coin door, and control panel, but is completely devoid of any connections to any other metal.

---. The wire used for the 115v connections is fairly thin, something like 20-22 AWG.

(I neglected to mention that the 115v wiring runs through an on/off switch at one point, and through a fuse at another).

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Questions

1. Am I correct that this is not a safe cabinet? 

2. Are the isolation transformer and Sprague Filter wired backwards? Where should the third wire of the isolation transformer (the yellow wire) be connected to? Where should the third wire (green) of the Sprague Filter be connected to? 

3. Shouldn't the metal grounding braid be connected to something in the cabinet (i.e. where should it be connected to)? If my monitor malfunctions, anyone touching the frame, coin door, or control panel is going to get zapped because the braid isn't grounded to anything, right?

4. Shouldn't the wire for the 115v connections be at least 18 AWG? Any reason I can't use stranded wire instead of solid core?

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The cabinet works, but I'm afraid to let anyone play it right now. Any advice is greatly appreciated!

--- John St.Clair
    Build Your Own Arcade Controls
    http://www.arcadecontrols.com/

[D_Zoot]

Saint,


The filter is wired on the right side.  The third wire at the filter is the ground and the ground lead (green) from the power cord should be attatched to that, also connect it to the metal base plate there, and then go ahead and connect the ground straps from the monitor, control panel and coin door to the base plate as well.  The whole point is to tie all of the metal in the cab to the ground in the power cord.


The third wire at the transformer would likely have been a tap for the original power supply in the cab and can be ignored since you have a switching power supply.

Yes, you can use stranded wire for hooking up inside the cab. 


Regards,
D

[RayB]

OK, here's the deal... there was a time when I would have said "yes! Unsafe! should all be grounded!" but recently I've started hearing some odd things...

For example, I was helping a guy install a switcher/MCR replacement in his Tron. It was bought from ArcadeShop. The owner told us the ground should not be connected to the power supply. (I can see in yours it's also not connected--The FG terminal screw). Why we're being given this type of instructions from a guy who's been in this business for a long time, I don't know... It goes contrary to everything I've learned about these beasts. Some games won't even work right if there's no grounding prong on the main power cord!

I think Ken Layton is probably going to have the best advice here out of anybody, so let's hope he reads this thread. :-)

~Ray

[grantspain]

your earth should always be connected,the braided earth strap is common on U.S built machines-basically every piece of exposed metal work on your cab should be earthed to protect against possible shock,also most componant parts(monitor,psu) require earths to protect against short circuit conditions and to protect sevice personnel,having said that in the U.S your external earth is not so important as you run at 120v as opposed to europe which runs at 220v,but like the first reply stated d zoot is spot on.
disconnected earth can cause proplems with your monitor,as in strange wavey lines and background static-in the u.k we have to test each machine every 6 months for earth bond.here's an example put 2 machines next to each other,one is earthed the other not,then if you touch each machine individually you will not feel anything but touch both machines at the same time(metalwork) you will recieve a half mains shock,it won't kill you but its not pleasant