Hi David , thank you for your help!
I disconnected the high voltage multiplier from ground ,lifting a jumper located on the upper side of the board (A5 coordinates on the layout).
Well this is what I observed :(note: I had another oscilloscope connected on the collector of Q1418)
pressing beam finder I got the trace ; I was able to catch a sinusoid of 25 volt peak to peak for 5 second , then nothing .
The trace disappeared but a sinusoid of 50 khz and amplitude 1 volt only peak to peak was visible on the other oscilloscope.
I started poking around and I noticed the blown fuse. I suspected C1419 (I had previously tested it ok) .Short circuit but no smoke , no popping out ,silent failure.After inserting another capacitor , everything seemed to function again , but it lasted only 5 second.
Tonight ,in the dark ,I was looking for some luminescence from the crt , to reassure myself that it was still ok , when suddenly the trace came on.
Note : the high voltage multiplier was still disconnected from ground . This time the trace was larger than before , occupying about 6 division.
I was able to change intensity , focus, move left and right, I also connected the calibrator , everything seemed to functioning perfect (apart for the postacceleration) . At this point I switched off the oscilloscope , to connect the other one: after switching on again no trace at all.
Due to my inexperience I am not able to relate these symptoms to a precise cause : are they showing a bad high voltage capacitor or a weak diode in the dc restorer section , or a weak transformer ? I am thinking that perhaps the high voltage multiplier is still good (or this is only a wishful thinking to avoid the inconvenience of find and installing a new one?).greetings and thanks