You should quit while you are ahead. Your laptop, your scope and you are all lucky to not have been burnt to a crisp! Clearly you have not had sufficient safety training and as MaxHeadroom has pointed out repeatedly, there is no point in scoping the secondary, which is a dangerous activity.

 

You seem completely immune to safety warnings while happily conneciting things to literally deadly voltages in your admitted ignorance. Not even the sounds of arcing caused you to rethink this project.

PLEASE, stop doing this unless you actually know what you are doing. Which you, yourself tell us you don’t!

 

Well, as others have said, you could potentially measure this with the resistor but, without proper knowledge and procedure, you will eventually suffer injury or property/life loss.

This is one of these scenarios that you can't learn all the nooks and crannies of safety from a Youtube or a forum like this. These transformers can yield a lot of energy on the secondary and, with anything high voltage, the physical distances and clearances across parts are fundamental guards against problems - you will surely be surprised as how voltage can flow across otherwise perfectly normal air gaps. Also, the normal parts and design tolerances are being stressed to their limit - the laptop power supply being an example here.

 

I've taken a couple jolts of high voltage in the past AND IT IS NOT FUN (once by carelessly coming into contact with a HV tripler input in TV repair lab, and once when I was checking out an old tube-type oscilloscope). The tripler left me with a bit of scar tissue under the skin on my thumb, and the scope had me wondering if someone had come up behind me and kicked me in the pants (I got rid of it soon after).

There should be a high-voltage probe available for the multimeter, and I would STRONGLY suggest you get one if you insist on messing around with transformers like this one.

 

Our concern is real! I'm sure most of us are advising you from personal experiences. Many years ago I made a mistake, working on a 600V circuit which I thought I had unplugged. It threw me through a plywood wall. It wasn't fun! Take all the precautions you can and don't tempt fate!

 

Our concern is real! I'm sure most of us are advising you from personal experiences. Many years ago I made a mistake, working on a 600V circuit which I thought I had unplugged. It threw me through a plywood wall. It wasn't fun! Take all the precautions you can and don't tempt fate!

When I was about 10, I plugged (actually, wired) a board from a disassembled portable radio into the wall outlet. The capacitors on the board exploded and scared the hell out of me. I was lucky, I learned about the dangers of higher voltages without actually getting a shock.

I went on to get a few shocks, but they probably would have been more serious if I wasn't already very leery of AC mains.

 

If you grounded what was intended to be the HV output, then the other end of that winding which was intended to at ground potential would now be at a very high voltage. It may not have insulation to withstand that and so might arc to the primary or frame of transformer.

As already said, don't do it.

 

I think this is a good time to close this thread. Please stop experimenting with lethal voltages.