Downloaded the pdf. You're right. I was twisting knobs at random.
I read through and set the scope as per TEK 7704 Instruction pdf initially but until wiggling, twisting and pushing every knob and switch, there was no activity at all on screen.
The youtube vid actually captured the first blip and was a surprise to me.
I expected to show you all a blank screen.
As for my knowledge of oscilloscopes, my erratic Velleman was used to diagnose intermittent automotive drivability issues.
Obsolete now, with data logging.
I did replace a power supply transistor in it once, which was a service bulletin from Velleman.
So I guess that would be my oscilloscope repair experience!