The screen turn completly red after about 20 min being on

Usually that is a sign that your red picture tube is ailing. However there is a chance that it can be adjusted out, at least buy you time worst case.There is a voltage control in the front of the TV, you have to remove the bottom front half of tv to get to it. Some Sony's have 2 screws hiding at the bottom of set in front hidden behind 2 plastic covers,others just have screws along the backside.Be careful there are wires to front panel attached so remove slowly and leave wires on just move it out of your way..Once you remove that there is a small access panel to take off. You will see the voltage control (small plastic square with 6 knobs) The top knobs are focus controls for each tube the bottoms are for voltage adjust. The far right knobs are for red.So you can turn the red voltage control SLOWLY to the left,this will reduce voltage.Reduce until you see the red lines disappear. If you go too far one way or the other with the voltage control the tv will shut down and you'll waste time readjusting and turning set on until it stays on. If you can't adjust it enough to get all the red out without shuting down tv tube is in too bad of shape.