Sony KP-51HW40 51in

I do believe your red color tube will need to be replaced.

Sounds like the picture tubes are failing,common on sony. do you notice any thin horizontal lines? You mite get lucky and be able to adjust the voltages. Remove back cover and look inside to see which tubes are lighting up.The front panel below the screen will come off and behind it is a small access cover.remove it. there you will find the voltage controls (its a plastic square with 6 knobs). 2 knobs for each tube, 1 is focus the other is the voltage labeled "screen". they are marked so look closely. Green is always in the middle but sometimes they flip the controls for red and blue so pay attention to which you are controlling .slowly adjust screen voltages to see if you can get it to stay on. If you over do it those thin horizontal lines will pop up and the tv will shut off again. If you already have lines back off the voltage by turning knob to the left slowly until they diappear. If that seems to fix it but the problem but it comes back later, then the tubes are shot. good luck!

tv has a blanking picture mute circuit. adjust the screen controls which are located behind the speaker grill in front of set. there will be a access panel to unscrew in center and then you will see a black 4 inch square box with 6 physical knobs. 3 control screen the other 3 controls focus for red, green, blue. turn them down and slowly start turning them up. fixed.

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.

Try this....

http://www.somelifeblog.com/2007/06/sony-projection-tv-red-line-repair.html

These sets have weak picture tubes, this may buy you some time. It is not worth changing the tubes in the set. The cost would be more then its worth. Try these adjustments until it completely dies. I have the same set.

Go here for a detailed adjustment that may fix your problem

http://www.somelifeblog.com/2007/06/sony-projection-tv-red-line-repair.html

Can be 1 of 2 things. 1st the red tube just needs the voltage to it turned down. In the front of TV (you have to remove the lower front half of TV to access it) is a plastic square with 6 knobs. The from left to right top knobs control focus for blue,green red. The bottom knobs control voltage to each tube in same order (so lower right knob for red) turn SLOWLY to left to reduce voltage until excessive red and lines go away. If you over turn left or right set will turn off. If that does not fix it or if lines reappear then option 2 is that red picture tube is failing outright and needs replacement.

this is a common fault adjust the little black box in front behind the small wooden cover. you will see 6 controls don't adjust any of the top 3 only the bottom knobs 1 for each color. slowly back the control counterclockwise turn the set on and wait untill it shows a picture, slowly adjust the control for the color in question utill the color balance is correct- black and white with the color setting turned down all the way with the user menu when balance is ok you are all set.. turn the color back up with user control. rtepeat process if needed.

completly remove speaker cover untill you can see the electronics. there will be a box with 6 setting screws. on the bottom row of screws , look for the screw with the letter r under it .  verry verry slowly turn that screw counter clock wise untill the picture clears up . good luck

to thus problem its very simple .! try to resolder at the back of the picture tube board.