WG 19k7901 Ground Issue

Antifrodis

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Here's my latest problem. I haven't run into something like this before.

I recently decided to swap my Track & Field guts from one beat up T&F cab to another. The WG 19k4906 in the old cab was giving me trouble. The WG 19k7901 in the "new" cab was working great with a JAMMA setup. I removed the JAMMA harness, and rewired things using the harness I had for T&F. Everything booted up fine, except that I seemed to have some interference rolling down the screen on the 7901. I immediately thought there was a grounding issue. There was no ground post on the power plug. Furthermore, it appeared that the monitor housing was not grounded, as I found a loose green wire with a terminal at the end. This same wire in my other cab is attached to a screw on the right side of the monitor frame. I replaced the plug with a 3 prong plug, and I attached the green wire to the monitor. I powered up and blew the fuse on the monitor chassis.

My next move was to discharge the monitor and change out the fuse. Then I got the power schematic from the manual and used that, in combination with my old cab, to try and make sure everything matched up. I re-soldered the wiring on the fuse block, removed a workaround that eliminated the original top power switch and got the switch back into circuit. I tested the switch for continuity and it seems to function properly. I got everything wired back up and made sure everything was grounded as it should be (coin door, control panel, monitor chassis, iso transformer, switching power supply). I powered back up without the PCB connected to the harness and blew the fuse on the chassis again.

So my question is, would there be there any reason why I can't ground the monitor housing? Is there any reason I shouldn't? It appeared to be working fine without the ground, other than the fact that the picture was noisy. Furthermore, the ground wire wasn't connected to the monitor frame when it was a JAMMA cab, and as far as I remember, there was no noise on the monitor when it was JAMMA-tized. I need some ideas as to what to check next.

Thanks for any advice in advance.
 
It kind of sounds like you've got some sort of short to ground somewhere, so when you put the ground on the monitor, you're shorting the isolated monitor frame to the ground which is somehow shorted to the ac or maybe a stray dc voltage or something.

Try disconnecting all the grounds, except for the main wall ground, and then it daisy chaining to your monitor and see if it blows the fuse. Then you can add them back one by one and see which one blows it.

If the first one doesn't fix the interference on the monitor, though it would probably all be a waste of time at that point...

Interference sometimes comes from the power supply, too. So maybe it's just giving you a dirty picture...
 
Thanks for the advice. I am assuming that I would have continuity someplace between the hot and ground or neutral and ground if this were the case. I don't seem to have that issue.

So while I was going over the wiring again, I made the discovery that the 220v jumper was connected to the ISO transformer instead of the 110v! I've owned this machine for several months and was playing it without issue with this setup. I did notice that the neutral was still jumpered at the fuse for 110v and it did have a blown fuse going across the neutral. I removed that fuse and cleaned up the ugly looking solder joints in that area before I blew the last monitor chassis fuse.

So my next question is, what harm would the 220v jumper do? I mean, I'm only running at 110v coming from the wall. So was it okay to have it wired for 220v? I switched it back to 110v, but I still haven't plugged it back in yet. I'm checking over some other stuff first.
 
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