Ghost voltage on diode 1

[cmb042]

This really has me at a loss. I am reading a voltage across diodes when the diode isn't connected to anything. I am testing a circuit, measuring the voltage from the back side of the diode to ground (AC input). I switch off the power and the diode still has around 150mV across it. I unplug the souce, still there, I remove the diode from the circuit, still there. I try another diode that wasn't part of the circuit, same reading. I try a different mmultimeter, no change. Any ideas? I tried shorting the diodes thinking maybe some residual voltage across the junction, some capacitance, didn't stop the reading. I tried multiple meters so that rules out feedback from the meter, although they were both digital FLUKEs.

What could be causing this and how do I eliminate it?

 

[RobertLewis]

Besides hooking up an O-scope, try hooking up a high impedance audio amplifier (cap coupled) to the diode. I suspect that you are detecting an A.M. signal of some sort. You may be shocked(amazed) by what you hear thru your audio amplifier. RL

 

[biff44]

It is likely that the diode is rectifying stray RF fields, and showing up as a DC voltage. Your high impedance voltmeter is allowing this voltage to build up, and the test leads are acting like antennas. You can check to see if this is the case by putting a 1 uF ceramic capacitor in parallel to the diode and see if the DC voltage goes away.