Buzzing from speakers after arcade transporting?

[pcm2a]

I acquired a devil zone cocktail machine today. It was strapped down in my truck bed for a couple hours and when I plugged it in there is some buzzing noise coming from the speakers. The audio is still fine but you can hear the buzzing at all times, even when there is no audio. Before moving it there was no buzzing. My question is what are the things to check for this? I already tried a few different wall sockets to make sure it wasn't a plug issue.

Also, what is this thing underneath the machine? The metal with black ovalish thing, not the plug and on/off switch...

[yotsuya]

That's a transistor of some sort.

Make sure all the ground connections are solid in the cab.

[pcm2a]

So far I haven't found a dangling wire. I also tightened up the main ground wire coming in from the wall, with no effect. However, in the process I did find something real interesting. With the side of the cocktail open, there is no buzz! Close the door and the buzz is there. Mounted on the door panel is the game board and audio board.

Test:
1. Open door fully, no buzz
2. Slowly move door panel towards closing, buzz slowly coming back
3. Get door up near the close position, buzz is back.

I assume that as the audio board get's near the monitor it's picking up some interference?

[big10p]

I guess it could be getting interference from an outside source. Got any large electrical appliances near it, or speakers, things like that? Try moving the cab to a different spot, if you can, and see if that makes a difference. Just a thought.

[pcm2a]

I tried moving it around the room and I also tried running a long extension coord into some other rooms, no difference. The cocktail is not near anything except a brick wall. When you close the door on the machine it puts the game board and audio board about 3 inches from the monitor and all the other guts of the machine. If I can figure out how to safely disconnect the monitor I would try firing it up with the monitor off to see if it is causing the interference.

[big10p]

I doubt testing with the monitor off is worth it, when you say it was fine before you transported the cab home. Or, maybe the buzzing was there when you picked it up, but just didn't notice it?

Anyway, as yotsuya suggested, buzzing on the speaker can be caused by a grounding issue (grounding loop).

[pcm2a]

No way I missed this buzzing. The ground loop sounds the most likely, I'm jist not sure how to find it. I've looked for any visually unconnected or loose wires.

Update: My gut kept telling me to unhook the monitor. I unplugged the monitor, no buzz. The game still works, audio works, just no monitor and no buzzing. I'm not sure what this means or what to do next, but I feel like this pinpoints the problem.

[yotsuya]

It's a grounding issue, bro. Make sure the monitor is grounded.

[big10p]

And don't rely on a visual check. Check your ground connection gets continuity on a multimeter.

[pcm2a]

Right, I just am not sure which is the ground connection for the monitor. I've previously tested the ground on the jamma harness with my multimeter and it was solid.

[yotsuya]

You might want to post this in the monitor section - there are some guys in there that know their stuff, but they only frequent that forum.

[pcm2a]

Thanks I posted over there and hopefully someone can help pinpoint the ground issue.

[pcm2a]

I can say for sure that the black metal thing on the bottom gets monster hot.

[big10p]

That's why that transistor is mounted externally on a heat sink. They can get hot due to the amount of current passing through them. Nothing to get alarmed about.

[behrmr]

I could be wrong but looking at your picture it looks like your cabinet is not earth grounded.  I can see where it looks like someone installed a new power cord and cut the earth ground.  Follow your power cord in from the wall.  You should have black and white for A/C and green for earth ground.  The green should go to a metal part in your cabinet and then all other metal parts (including your monitor) should tie to that. 

[pcm2a]

In this first image the blue arrow is the 3 wire plug coming in. The yellow arrow is the ground wire connecting to the chasis and then jumping to another metal piece.



Here is another view of the chasis with the ground wires jumping around.



Finally here is one of two wires coming out of this power source unit. The blue arrow is where they connect to the power source unit and the yellow arrow is the other end which is a plug adapter. The monitor is plugged into that thing.