as soon as I put the (isolated) scope ground clip on Tip, I get a buzz, which you can see in the trace. I don't know why that happens, and it doesn't happen for the "good" line.
Are you using an isolation transformer to power the scope? It occurred to me that the ground is not isolated on most, just the line. That's why I suggested the adapter as a ground lift. But no matter.
On the bad line I can see garbage from 450-700ms that happens earlier and ends after about 425ms on the good line. Betcha that's your problem and why the 600ms delay stops it.
-Hal
