Video Interference [herringbone] but I don't use an arcade PSU

[mmoreira]

Hi guys, can someone help me?

I'm just converted my arcade machine into a MAME machine. Now my image has much interference, and the pattern is consistent with the "herringbone". I read the solution proposed by Ken Layton on this topic: http://forum.arcadecontrols.com/index.php?topic=20034.0, but I don't use the arcade PSU anymore. It's totally disconnected now (I not even sure I still have it), so I want to know how to do this with my PC ATX PSU, if its possible.
Or (if I found my arcade PSU) how can I use it together with the computer to solve the problem.

I also read this topic: http://forum.arcadecontrols.com/index.php?topic=130774.0  but I didn't understood how the guy solved it. It says: "I attached the FG and GND on the 24V FFB PCB PSU". I don't have any 24v on my ATX PSU and I don't think short-circuit 24v and ground makes any sense.


Thank you for your attention, people!

PS: Sorry for my bad English, it's not my primary language and I only have limited skills with it. If I was not clear with my question, please tell me so I can try to reformulate it.


Teus.

[MonMotha]

PC power supplies always have their DC common (black wire) connected to earth ground (safety wire on the AC cord, usually green and sometimes with a yellow stripe).

If you wanted to float it, you could use a cheater plug, but be aware that this is a somewhat hazardous condition.  At minimum, it will zap you if you complete the circuit to earth, but not badly if everything's operating correctly.  The reason is that the EMI filter capacitors in the supply will leak about 60VAC to the DC common, but it's quite limited in current.  Normally this just gets shunted away via the earth ground connection, but if you remove this connection by using a cheater plug or similar, it won't have that path.