Desperado, back in post #1712 Daver2 gave you the instructions about using Channel 2 to look at the pulses on UD9/20.
When you are using just one scope channel like this, it works much better, as noted by SiriusHardware if the scope is not in dual mode, because you will always get a brighter beam, with the single trace only and not a double trace.
Sometimes, in the DUAL channel mode, the effect of the Chopping process inside the scope, between channels (and channel 1&2 beams on the CRT face), can produce artifacts (a false signal) that might look like real signal but it is just the scope chopping between beams, like you have seen in your video post #1747, but is not a real signal at all, this tends to happen, when it does, at very fast (short) time-base settings.When this becomes problematic often using ALT rather than CHOP can help.
So follow Daver2's and SiriusHardwarte instructions exactly and for now just channel 2 operating, not in DUAL mode, and see if you can find and lock the pulses on UD9/20 if they are there.