I recently picked up an Arena, and it has a Swemmer cpu, Ni-Wumph driver, and a gulf pinball power supply. Sound board is original. Today I was messing around with it and the game would randomly go haywire. Lights flashing, random sounds, garbled displays. I started with checking 5v everywhere. If I check the 5v at the MPU connector, and sound board connector, or the 5v out put on the power supply with the negative lead on my dmm grounded to the grounds at all those locations including the directly bolted ground at the bottom of the backbox I get 4.88 volts. But if I put the negative lead on the ground that comes in next to the 14v input at the power supply I get 5.05 volts everywhere I check. The previous owner did the ground mods at the transformer panel. And this gulf power supply doesn't have an adjustable pot for the 5v. Any ideas why there would be a .15 voltage drop between the grounds and 5v lines at the connectors going to the boards? Thanks