I think he is referring to the 'trace brightening'.
From your video, when you were using the second timebase, you will note that the first timebase had a short length of it brightened. This brightened section tells you which part of the second timebase (fast timebase) will be seen. I think the trace brightening will be a signal generated as an output from the first timebase sweep and will feed into the intensity control system.
However, I would be inclined NOT to poke around with something as good as you have. I can look at the circuit for you if you wish, but again, I suggest you take the manual to bed and read it there. I did remark somewhere, that jitter on these kinds of dual trace measurements can be adjusted out by understanding the triggering controls. I cant stress too much, how important it is for you to get your drivers licence first before you start imagining problems that dont exist.
Thank you for your comments
Yes, I understand the workings of the dual timebase, and the bright area being the "selected" portion which you are zooming into; I don't think the guy I was talking to was referring to this - he was talking about 1M resistor(s) going high with age to about 1.3M etc, and how some capacitors went a bit resistive, and how, when they were replaced, the visibility of
very fast signal traces was improved somewhat. The bloke I am talking is, I'd say, around 65-70 years old and is the manager of a NATO approved test equipment repair and recycling company, so I'd say he knows his stuff - he told me in INTRICATE detail how to repair the tiny plastic "doors" that let the flourescent green plastic indicator through on the power switch, and was on the phone for ages explaining many, many more in-depth intricacies of which Tek scopes were best and worst, and the various repairs they come in for.
I agree that I'd not "fix" something that works perfectly okay, but I am asking because
I want to know, not necessarily because I am
going to attempt the repair. I want to "feel like a king", as someone said earlier in the thread - if
I chose to mess up my scope, that would be my problem... but I've no intention of doing so - I like learning things, and I am highly competent and learn rapidly, so maybe one day I will refresh the "bright-up" circuit he is referring to, once I am more adept and have a feel for this stuff
As regards needing to get to know the scope thoroughly... that's exactly what I am doing, and these kind of questions are part of that learning curve. Remember, we all learn in a different way, and I ask the specific questions that I ask, because that certain aspect is pertinent to me and to the way I use deductive reasoning in my thought processes and understanding. I really, really value your insight and cautionary comments toward me, though - I thank you for warning me; you don't know me, and I could be a complete klutz who is a butter-fingered solder splashing enthused amateur, eh! ^_^
Thank you