I have a JD-990 plumbed into a DAW that's picking
up computer noise whine. No 60 cycle hum.
It has the usual EIC 3-wire plug. The whine goes
away if I lift the 120 V ground which I don't like to do.
Looking at the schematic, there are five 1000 pF
and two .01 uF ceramic caps across the analog ground to case
ground.
With everything unplugged, the resistance from the
case to the analog ground is 0.3 ohms, basically the resistance of the
meter leads. Shouldn't the case to analog ground
be nearly open if they're putting capacitors across it? What good would that
do?
I'm thinking one of the caps is shorted. I
checked the two 0.01 uF caps and they're ok, so it would have to be one of
the 1000 pF parts.
It has the original caps on the power supply
fwiw...
Thoughts appreciated!
Scott in Ohio