Hi EEVblog people, I was trying to assist dukebubs with his oscilloscope before they posted on here (at my suggestion). I'll try provide a summary of what we checked together.
Firstly, we attempted basic calibration of the oscilloscope, without much success - the trace was always off-screen. I guided them through safely opening it up (small brief on the dangers of CRTs and oscilloscope circuits) and directed him toward some of the adjustment pots on the vertical amp board. The boards and adjustments in the manual didn't line up exactly with the physical version of the board (possibly a different revision?) and at some point before bubs purchased it there appears to have been some additions made to the circuit on the back with additional pots and resistors wired in - they didn't appear in the service manual. The display does show a portion of a trace, and some of the pots have influenced it, but nothing significant.
Here's the manual
https://www.download-service-manuals.com/download.php?filename=Leader--LBO-522--user_and_schematics--ID3791.pdf and the pots that we tried adjusting were all on the vertical amp board (page 24 of the pdf file). We started with the vertical position pots, then the vertical gain 1x and 10x pots. After that several other pots were tried, including the two additional ones that someone hand-soldered in place, those hand soldered ones appear to be sort of compensation for initial voltage spike compensation (the start of the square wave was influenced by it).
We didn't probe anything with a multimeter yet, but as the pots didn't line up with the manual exactly, I might have strugged to give good, safe direction on where and how.