In article , you say...

Are you focussing on the fact that all three had to be done, or that
they had to be done in that particular order?

There is, in fact, a very sound reason for switching the TV set off first.

Many sets used the 'off' switch action to force the brightness to maximum,
thus discharging the EHT reservoir rapidly before the scan collapsed
completely.

Failing to use the set's own switch resulted in the dreaded switch-off spot
which would ultimately cause a phosphor burn.

Normally I would not be in favour of going to all the trouble of switching
off the socket and unplugging the set but I recall one occasion when it might
have saved a set from destruction.

Following a thunderstorm in which the aerial was struck by lightning, two
blackened holes had been drilled through the paxolin panel holding the aerial
isolation components (a shorter distance than through the components
themselves!), the mains switch contacts had been welded together and the
lightning had jumped from the 13A plug to the socket on the wall - over two
feet away, according to the customer!

On the same night, about 2 miles away, another set was left plugged into the
mains. In this case, no trace of the aerial was ever found(!) the tuner unit
in the TV was completely incinerated inside, the mains switch contacts were
welded and the fuses in the consumer unit blown!

Fortunately the set was only a couple of years old and a replacement tuner
was still available. In the case of the other set, it was too old for a
replacement and would have had to be written off if it had sustained the same
damage ...

The first set was a Bush TV53 and the second a Bush TV98, if anybody wants to
attempt to date this!

--

Terry