Re: De-gauss button
OK, I'll bite..
The De-gauss button demagnetises the CRT. The CRT will build up a certain amount of magnetism over time (and I cannot remember why but it's not that complicated) Any residual magnetism in a CRT will cause the cathode rays to not go exactly where you'd like them and so the red beam might end up hitting some of the green phosphors, the blue the red etc but not necessarily over the entire display.
CRT's are/were a nightmare IMHO in so many ways..... I don't care what many of my fellow TV engineers say.
A coil of wire is wrapped around the front of the CRT and when you press the de-gauss button it is energised with an AC current which diminishes to next-to-nothing over a couple of seconds. The coil of wire is therefore magnetising the CRT +ve then -ve by each half cycle of the diminishing AC - going around a hysteresis loop to remove as much stored magnetism as possible. (This is how tape head demagnetising is done) The magnetic field also affects the RGB cathode rays hence the wobbly picture.
On many monitors and TVs the degauss was done at switch on - which is the "thung............" sound you hear - You would not normally see the picture wobble as the CRT heater gun had not warmed up at this point.
One other thing about degaussing - it also set the CRT to be correct for its orientation with the earth's magnetic field and so ideally it should be done with the CRT in situ - if you have one which gets moved about a lot......
There's probably a much better explanation somewhere on the internet.