So if i don't have any isolation transformer, is there any other ways to measure it.( i very sure that my scope is grounded).this circuit just isn't going to work for you without an isolation transformer
i've learned some of this the hard way repairing power supplies.
Can u explain about this way in more detail? What is the digital unit that u mean?use a digital unit that connects to a laptop and unplug it while probing on a line connected device.
Hi Bill,If you have a dual channel scope, check to see if there is an "ADD" function where the two inputs are added together. If so, use one as the "common" and measure with the other. Scope remains grounded and safe.
You may want to look here:
http://www.allaboutcircuits.com/worksheets/scope1.html
Paying special attention to question 11.
creakndale
by Don Wilcher