PC/VGA interference troubleshooting

[Lowballs]

Hey Guys,

I have an issue with a wobbling screen when using a PC. Everything works 100% as far as I can tell when using an arcade PCB, but when the PC is connected the image wobbles like crazy.  I think this is due to the earth from the PC mains interfering with the image.

PC is pretty much completely separate to the chassis and no earth between.

I found this thread from years ago on here which is essentially the exact same issue I'm having - http://forum.arcadecontrols.com/index.php?topic=106123.0

Things I've tried:

Unplugging the Arcade PSU
A different video card
Earthing the VGA cable to the chassis tray
A different PC (out of the cabinet)
Different power sockets in the wall

Any help would be awesome!

Cheers.

[Zebra]

Post a video of the problem so we can see what you mean by "the image wobbles". That could mean a few different things with very different solutions.

[Lowballs]

Apologies. Video below.

[Zebra]

Are you running an interlaced resolution and are you using an Extron RGB interface?

It's hard to tell from that video but it kinda looks like the flicker you get in displays that aren't optimized for interlaced modes. It also looks like what happens when I flick the disable digital signal processing dip switch on my Extron interface.

Are there any other devices between the source and the monitor? And have you tried a different cable?

[Lowballs]

Are you running an interlaced resolution and are you using an Extron RGB interface?

It's hard to tell from that video but it kinda looks like the flicker you get in displays that aren't optimized for interlaced modes. It also looks like what happens when I flick the disable digital signal processing dip switch on my Extron interface.

Are there any other devices between the source and the monitor? And have you tried a different cable?

Hey Zebra,

Pretty new to this but will try to answer as best I can.

The video above is a bootable Linux version of GroovyArcade. That's the initial splash screen to select resolution. I'm not sure how to determine whether it is interlaced or not at that point I have also tried this in a Windows 7 Pro installation with GroovyMame and CRT_Emudriver. I have tried 15khz and 31khz with the same results. The chassis is a Toshiba PB9929. It does have an RGB input but I'm purely using VGA. There's only one switch on the chassis. I think it's the horizontal position switch but I'm not sure (attached)

For the most part the VGA cable has been running direct from the PC to the plug on the chassis (images attached), I did try it via the JPAC and have a few cables I've used as well.

[Zebra]

If you installed crt emu in Windows in 15khz mode, I believe the default res (for the Windows desktop) is 480i. That kind of flicker is not unusual for 480i on some monitors.

There's s simple test to see if this is the problem. Run a 240p game in Groovymame like Street Fighter 2. If the issue goes away in 240p, there's nothing to be done (aside from changing monitors if having 480i is important).

Also, take a look at your settings in vm maker / arcade OSD. Did you select composite sync or did you leave it unchecked? It looks like your monitor connection is RGBHV, not RGBS. It's probably not this but it's worth looking just in case.

[Lowballs]

Finally managed to fix it by running a separate ground wire from the monitor frame to the wall. No more judder!

Thanks Zebra for your suggestions.