had a similar fault on a ducksan this week,the machine had been switched off for over 2 years,when powered up(after many repairs) then screen was well out of focus and dark-i left the machine on for 24 hours for the tube to climatise then adjusted the focus and screen volts,now is fine.worth just trying this first otherwise there could be a poor connection on the wires coming from the lopti to the tube base,or worse your lopti or tube.