15 May
2008
15 May
'08
10:47 a.m.
On May 15, 2008, at 11:50 AM, Jeff Erwin wrote:
Case solved (I think). It seems to matter where I
ground the
probe. I
pulled all of the boards out of the system, no change. I then
grounded the
probe to the middle finger of the voltage regulator on the board
and the
sine wave went away.
The chassis may not be at digital ground.
Also watch out for the middle lead of three-terminal (78xx/79xx)
voltage regulators...it's not unheard of to bring them up above
ground a bit with a voltage divider to make them operate at different
voltages.
-Dave
--
Dave McGuire
Port Charlotte, FL