good work young man!

I was yelling and waving at my screen there for a moment until you found the channel A "GND" switch! As for the ripple on A but not on B, have you checked the power supplies? I wouldn't be surprised if HP designed the scope with separate power supplies for the A and B channels, and one of them has a bad filter capacitor. Worthwhile checking all the power rails in the instrument, both with the multimeter and with another scope.

Cool stuff

Looks like the main filter capacitors reformed and thus the ripple got less

The resistor is needed with low parasitic inductance. I hope the author of the video took this into account. :)

it would be interesting to know if you ever actually got any use out of the repaired scope....or has it been turned off since the end of this video......if you found a use for it then it was ten dollars well spent

Looks Great, I am sure you will figure it out, next time I would like to see a Fluke meter and not a Radio Shack one! Get "G" to fork up some dough! LOL