Thanks Siggi, I have just tested every resistor you listed out of circuit, they all test good and they are still in spec even the 1% tolerance ones, I replaced R1878 when I received the scope, the previous owner butchered it, probably the grid bias problem was there when he sold the scope, I also replaced c1991, just to be sure it wasn't leaking. The only thing I found a bit strange is the waveform from pin 7 of high voltage trasformer, the sinewave seems a bit asymmetrical, however -300v test point is exactly at -300V. Thanks again.
Regards
Francesco.
