Question concerning grounding of a Mame Computer

[Honzo]

So my idea is to mount the motherboard of the computer I'm using to the inside of the cabinet the same way the original boards were, but I got to thinking about how a motherboard is mounted in a computer case.  On the back side of the board, the screw hole surround is exposed contact, then the standoffs, case, and psu case are metal, so theres a clear connection to the power supply from the back of the screw holes.  My question is whether this connection is necessary.  If i mount the board on the plastic standoffs and theres no longer that connection between the motherboard (through the standoffs and case) to the psu, will i run into any electrical problems? Thanks for any answers.

[swamprat96]

Good question. It will normally run fine just mounted to timber and isolated- but I always add a ground braid between them and other metal parts and then to the ground of the cab. Is it necessary? Dunno- but I was told its a good idea

[SavannahLion]

Depends on the motherboard really. I have one board where, despite metal standoffs, screws and back plate, ceramic discs are inserted between screw/standoff to isolate the board. Not sure why this but it is an older board (300MHz era) so it doesn't concern me much anymore.

Back to the question at hand:

My question is whether this connection is necessary.  If i mount the board on the plastic standoffs and theres no longer that connection between the motherboard (through the standoffs and case) to the psu, will i run into any electrical problems?

Depends on your luck. I run motherboards without cases at all for long periods and never run into a single problem. I have a few boards where ground was broken for some reason and I got all sorts of really weird behavior that were almost impossible to track down. Weird memory errors, odd HDD reads, graphic glitches, random power switches (a convoluted problem involving a refrigerator, dirty power and a broken ground).

I'm not really an expert at this but from what I understand, the whole point of having those ground contacts on the board like that is to create as wide a path for ground to take. When you restrict or break the path to ground then you create an area of unknown potential or capacitance(?). On older arcade boards, I guess this isn't much of an issue. As the board speeds go up, having a well established ground becomes more important.

I say this. Try it on wood. If you start getting unexplainable errors or odd behavior, then buy a sheet of sized conducting metal, drill your holes (or find an old or cheap compatible PC case and cut the mounting plate out) and remount inside the cabinet using metal standoffs.

I honestly don't know if I would go with what swamprat96 suggests using braid. I think the potential for the ground braid moving and shorting out other components or coming loose and shorting things out makes me too uncomfortable to use as an option. Maybe use insulate wire and crimp/weld using ring terminals might be a safer option?

[severdhed]

i've had mine mounted to the wood in the cabinet for a few years now, and no problems. 

[getnate]

I ripped apart an old ATX case and took out the motherboard mounting plate/sheet. Then I attached the motherboard like normal to the plate and screwed the plate onto the inside of the cab. As a side effect, I had extra space on the plate and was able to screw the PSU and HDD onto it. Now the whole PC is a single piece.

Most cheap cases are held together with rivets. The easiest way to take them apart is drill out the rivets with a power drill. It worked great for me and I didn't have to bend, rip or cut and metal.

[swamprat96]

When I use braid I use a staple gun and staple it securely to the inside of the cabinet so there is no slack or loose cable hanging around. Exactly the same method they use in Pinballs for the last 30 years.....

[matman]

I have mine mounted to wood also, but since it isn't grounded i'm getting hum in the audio.  Searching led me to this:
http://forum.arcadecontrols.com/index.php?topic=89559.0

which basically indicates wiring to the PSU gets rid of the hum and grounds the motherboard...probably a good idea regardless of the hum.

[Sky Zero]

Exactly how do you go about wiring from the PSU to the motherboard? Did you just tape the wire to the side of the PSU case or use one of the screwholes? I'm getting a hum in my audio when I plug my amp into the mobo and this might help solve it.

[Beretta]

usually this is not nessary, when it comes to cases it's more a matter of safety then anything.

having the case grounded means if there is a short it is shunted to ground.. so when you touch it you dont get zapped.

it's normally not nessary to ground to the PSU, however if you feel it nessary it wont hurt.
what i would get is a small nut+bolt, put it though a mounting hole and wrap a wire around said bolt then tighten it down.

18-22ga wire should do the trick.

for the psu just wrap the other end around a screw and tighten it down on one of it's mounting holes.

no need to crack open the PSU because it's housing is grounded.

again not usually necessary but it certainly wont hurt.