MY SCREEN SHOWS ONLY A BRIGHT LINE STRAIT ACROSS

you more than likely have a coupling capacitor defective in the vertical driver/output circuitry,or you can have "COLD"solder joints in these or the power supply section,carefully tap in every area on the case,if picture starts to expand and collapse, then its a solder joint thats bad/if you can take back cover off take an insulated plastic instrument and tap and push on board and components to see if you get the same results...be careful inside case