Is the Bench DVM meter chassis ground connected to the meters probes?
The meter probes would have to be internally inside the bench DVM meter connected to earth or chassis ground of the DVM meter
If a circuit boards power supply earth or chassis is different then the DVM meters chassis ground or earth ground can this cause a ground loop or short when measuring from VCC to VDD rails?
When can a SHORT occur when measuring from VCC to VDD supply rails?
Does your "plug-in DVM" have a three-wire (Line, Neutral, and Ground) type of line cord? If so, likely the DVM's black lead is internally connected to the Green ground wire in the line cord...
Does your "plug-in DVM" have a three-wire (Line, Neutral, and Ground) type of line cord? If so, likely the DVM's black lead is internally connected to the Green ground wire in the line cord
ARE YOU SURE tho that the black lead is connect directly to the green ground wire?
and how can i check this?
Is there any other way of having two different grounds or a ground loop that would cause a DIRECT short from VCC positive supply to VDD negative supply from using a PLUG IN DVM meter?
Would have two different EARTHS from a test fixture earth ground that is different than the circuit board earth ground cause a VCC positive supply to VDD negative supply short from using a Plug in dvm meter when measuring from VCC positive supply to VDD negative supply?
If you have another DMM, unplug the DVM and simply measure the resistance from Blk to the big prong...
btw-most 'scopes have this same problem: Ground clip on the probe connects to earth ground through the green wire in the line cord.
I would use a battery-powered Fluke DMM to make the measurement that shorted your supplie(s).
Many times a bench DVM might have a particular spec as to how far above ground the negative terminal can be. Keithley had it marked on the binding posts. 30 V is not unusual.
Isolated AC supplies to the equipment being tested is one way out, but then that equipment cannot have a ground.
If you have isolated AC supplies with two difference earths, and you measure the VCC positive supply to the VDD negative supply using a Plug in the wall type DVM meter Or O scope, will this cause a direct short?
Or what is causing this direct short from VCC positive supply to VDD negative supply, when measuring using a Plug in the way type DVM meter?