The Scotty black boxes had a "pulse" feature on them.......It could pulse between nothing and whatever voltage you had it set at. (At least on the digital versions).
Th entire time I used mine, I never tried that feature......so I can't say whether it would have made any difference or not.....
As I recall the Scotty black box also had a feature where:- if it was turned on and set at a certain point on the dial.....it would show you what your natural voltage was (both lines in the water) and then you could dial it in from there....
Still have my black box and all the stuff in the basement......you never know......one of these days.......
A prime point to check with the black box is where the wire connects to those stainless sleeves on the downrigger arm.
I found that point was highly subject to corrosion.
Also the sleeve itself.....it's just a sliding contact on the downrigger wire and i found i had to play around with mine for setup so that the sleeve was ALWAYS in contact with the wire no matter what was going on.....and you need the sleeve level on the wire so that you get maximum contact .
The sleeve itself needs to be "electrically clean" all the time.
I used that brake/electrical spray to get any film,glaze or dirt off the inside of the sleeves......