All good points above and I will go back and look for RF but this scope is a little different. Let me see if I can give you more scope below.
1) Sprinkled around the scope are about 10 - 15 pots that impact the horizontal and vertical positioning as well as the focus of the characters in the display. The horizontal and vertical pots impact the trace but focus has no impact on the trace, just the characters. You can tweak the focus of the corners, sides, rotation, astig, etc but nothing changes the trace width with the exception the brightness of the overall display.
2) The scope has a high accuracy mode that looks like it moves small lines within the graticule boxes in order to improve the accuracy of the horizontal and vertical trace. The scope must be able to see these lines somehow, maybe through the infrared touch screen? No idea how. Now that the trace is so wide, it fails the enhanced accuracy setup.
3) There is a display adjustment button that enables you to set the astig and max brightness for the characters and main trace as well as the delayed and XY modes. There is also a dial with a button next to it to enable you to set the brightness for the characters more dynamically instead of having to go into the display adjustment mode. I usually would keep it in the main trace as it helps to adjust the brightness depending on how many waveforms are on the display - more waveforms require the brightness to be brought up. At one point, I had the trace pretty narrow but the lower I went in frequency, the wider the trace became. Adjusting the brightness made the trace narrower so somehow the scope must change the trace focus based on brightness. Go figure, to much automation if you ask me.
4) In the service manual they teach about using calibration software, which I have but it runs on old dos, to set the trace calibration. I believe the issue with the trace is related to DAC voltages not being correctly stored and read from EPROM. I think all the voltages for focus and brightness related to the trace (for each horizontal setting) are stored and adjusted by DACs instead of pots like the character displays. This is what I need help with, finding the EPROM that stores these calibration constants, possibly replacing it, and then rerunning the calibration which I think is pretty much automatic.
This scope is huge, has tons of functions for an old scope, all discrete logic with a few micros. I don't know how it reads the trace and calibrates it but somehow I think it does. When you run the enhanced accuracy mode, it puts small lines up on the screen within specific graticule squares so it must be reading them back somehow. It also seems like it has a set and forget (with the pots) for the characters and some kind of dynamic adjustment for focus and brightness of the trace.
Let's see if this jogs some thoughts.
Thanks
Jerry