In article ,
John Smith I wrote:

Mike Chambers wrote:
...

Mike:

Here is an interesting link:

http://www.waypoint.com/users/~disco...esentation.htm

One circuit I seen on this page makes use of an opto-isolator. Seems to
me that with a led and photo-transistor one could kludge together a unit
which would seem to perform miracles!!!

The OP already tried a isolation transformer so I don't think an
opto-isolator will be any more helpful.

I expect that it is a common mode noise issue. He can buy common mode
chokes that just clamp on the cables to find out.

--
Telamon
Ventura, California