Ive watched daves video and alot on the same topic, and read alot of articles and its left me confused. Seems like back in the day everyone suggested isolating the device being scoped and now they dont.
Going to research it some more as ill ultimately end up using the scope to test crt monitor circuits and IC's.
The monitors have seperate power boards but not sure if the chassis board is connected to earth ground. Ill have to test for continuity between earth ground and the chassis board and how to safely probe these circuits.
Alot to learn
The "idea" or better the warning in most of the service manuals from CRT TVs are based on the fact that the chassis are not grounded to earth.
(2 pole mains plug).
And there are "hot", will mean the chassis gnd could have high potential, depending on how the mains plug is connected.
It´s a 50:50 chance to have neutral or phase on the chassis.
The scope´s input gnd is the same as it´s Earth potential.
So when the TV chassis it´s gnd have phase potential and you connect the gnd clip of your probe to chassis gnd for measuring....BAMM.
A 100:1 probe won´t protect you for this as it´s gnd is also the gnd of the scope/earth.
(When measuring with a DMM you don´t have this problem, ,but as mentioned before, with a DMM you won´t "see" everything.*)
To avoid this risk, the recommendation came up to use a galvanic transformer for the DUT.
(As I´ve started to work in the testfield here, the guys who were already there use the transformer to isolate the SCOPE...

)
Differential probes are more convenient to use, are not really isolating potentials from each other, got the advantage of switchable input dividers, got the possible disadvantage of noise when looking at lower signals, limited bandwith (for your purposes not remarkable).
There a cheap but good ones avaible from micsig.
Martin
*)
https://www.eevblog.com/forum/repair/hioki-3532-50-lcr-schematic-service-manual-wanted/msg4575439/#msg4575439Actual example why a DMM is often not enough..