I don´t understand why do you replace the CRT drivers and the HOT if
they are OK. I can understand that part about replacing aged
electrolytics, redoing any stressed solder joints and restoring the
CRT... but why to replace transistors if they are ok?

Because you are in there. It takes bench time $$$$ just to
open the thing, and so you don't take chances on the HOT,
flyback, power electrolytics, CRT board adjustments .. esp
the driver transistors and current limit resistors. All of those
points "heat cycle" badly, and the solder joints crack. That
causes any movement of the video cable to wiggle those
bad joints and glitch the picture in a million ways. A bench
tech can't spend time diagnosing that stuff. I just shotgun
all the potentially weak areas and run a bench test for about
an hour to watch the video cycle. If it works ... start praying
for 90 days. Otherwise .. MAD BOSS ... mad mad Boss !
Something else .. all those parts run about $30 total on the
bill. Stupid not to replace them. More stupid is to repair the
thing at all, but that is not my option, and some customers
simply believe in maintaining their hardware.

johns