This is where an old VTVM and 1090 meg HV probe come in handy. The self contained ones most people used for TV work could not measure negative voltages and it is a hell of alot easier to get to the cathode than the anode on a scope.

Those voltages are usually on the print, so you can tell if it is in regulation or not. If I am not mistaken, the dividing resistors for the focus are part of the HV regulation feedback loop, so a fairly accurate measurement of the cathode voltage can be quite useful. Also, turn it off and let it all discharge, then turn it on with the probe connected and see if you get HV for a split second and then goes away. If so it is going into shutdown, dead giveaway.

Most of the scopes we bought/buy we get a chance to plug them in and tend to get the ones that at least produce a trace. We are sorta in the market for one of those 1090 ohm jobs but the ones I see are a little to high for something that might get used once a year. Also that the market for them is so limited. So that means I get to wrestle with the fun ones, like B sweep not starting on a 465B. You REALLY want B sweep to work on a 465B because it has the split function where you can see the whole trace and the expanded trace at the same time. Even though it is not something you would use everyday, it is still a feature and it should work.

And don't overlook the possibility of a failure in the main power supply. Check everywhere it says 15V, 5V, 8V -5V, -15V, 130V, 50V, -50V and so forth.. Those seem to be the supply voltages Tek used to like to use.