Howdy -
Apologies in advance if this is a stupid question, but I've been scratching my head about an issue all week and it's driving me nuts.
The quick background: I am an EE student, and for one my classes (microelectronic devices) we are using some cobbled together step-down transformers in the lab for some of our rectification projects and other stuff. I decided I wanted to build my own identical transformer so I could do some extra experiments at home, and with the exact parts list in hand I did just that. Easy enough - it was just a 120V -> 12 V (center tap) transformer and a pile of breakers and fuses.
I tested my version of the transformer at the school's electronics lab, and was getting the same results as I did with the "official" lab transformers - specifically, the expect voltage between the ends of the secondary winding, or between an end and the center tap, with the DMM. Using the 'scope at the lab, the output was also unsurprising - a lovely sinusoid came out, with the probe on the post for the secondary winding end, and the ground clip on either the center tap or other secondary end.
NOW comes the rub. I brought my transformer home and did the same tests with my home 'scope and DMM. DMM results were the same, but the scope at home did NOT show a sinusoid. Instead, I got what the attached image shows - rather than a sinusoid, it looks considerably more like, say, a capacitor charging and discharging (at 60Hz) ...! I tried the measurement on four different circuits in the house with identical results.
So ... what am I seeing here? Am I going insane? Do I have some hideous load on my system that I'm not thinking off, that would affect all the circuits in the house? Or worst of all (worse than insane, even), do I have some fundamental problem in the wiring of my house - say, something screwy with the ground?
Thanks in advance for any help!
Jeff
p.s. (and yes, I did bring my home 'scope to the school lab to confirm that it wasn't a scope problem ... no dice)