I think he means that the top left is negative and the top right is positive, that the bottom right is ground and that he's not quite sure what the bottom left is.

The fact that a new plug was installed and works means that there was surely method in the madness. Still, I think I'm a-gonna get me a voltmeter before I play around with my 540c and its troubled power supply any further.

Must ... however ... restrict ... the ... monthly ... outflow ... of ... pennies ... on ... antiquated ... electronics. (That means I'll probably wait and tackle this one sometime in the new year.)