Everybody: Thanks for your help and suggestions.
Dear Ozan,
You definitely mentioned C1387 as a potential culprit and helped me locating it (some errors in the manual , hence I could not find it myself!).
The problem of an intermittent tantalum shortcut PLUS an intermittent break in the last part of the GND rail is uncommon.
Next week I will start to look where thee sweep generators have failed ( I think the last part of the horizontal AMP is OK, because the scope functions normally in XY mode and "Beamfinder mode",
I will start a new topic if I get stuck ' I definitely welcome your advice! A new puzzle, I'm afraid!
Regards, Martin
