In chasing some odd sound board behaviors, I was checking my ground and power inputs and found something a little disturbing.

I hooked up my scope to check the ripple on the 5 volt supply of the sound board and when the probe got near the metal side rails it showed that there was a fairly large voltage on the rail relative to ground. Using a multimeter it showed 60vAC on the side rail relative to the ground strap.

The ground strap that runs around the periphery of the machine shows zero ohms between the strap and the ground prong on the power plug.

I shoved the multimeter leads into the ungrounded utility outlet in the cabinet and it measured....60 volts. This was the equivalent of measuring across the hot/common of the power cord.

Needless to say the machine is unplugged now.

I checked the wall outlet by placing the multimeter probes in the blade slots and it measured 120v.

I am making the wild and crazy assumption that this qualifies as "not good", but I am not sure where the failure is.

Is there a diagram of the internal wiring between the power plug and the transformer? I have seen snippets of something like this but I have not found the document myself.

Any ideas?

Let me add 2 things:

I tested the outlet with one of those little 3 light testers and it says that it is good.

I got 60vAC on the internal service outlet with the machine power off. This would seem to indicate to me that there is a problem with EMI filter. With the power off, there is no power on the rails relative to ground.

Fluke MM set to AC....

And I need to put a hold on this. I retested the connectivity between the ground pin on the plug and the internal ground strap and low and behold...it varied. I have a bad something somewhere in the power cord. Will replace cord and retest sometime in the next 24 hrs.

With some embarrassment, I have to report that my issue was a flakey ground pin on an older power cable. Tested OK when I first got the machine and was touch and go over the last few tests.

New power cable = no problem.