my sony kp53s70 is not working

i have a sony kp53s70 tv i picked up last year. it would not turn on iwas told that the flyback transformer needed to be replaced plus the horizontal output transistor.i was lucky and only had to replace the horizontal transistor the tv worked good for about a year then shut down again. i  replaced the horizontal transistor again it worked for 5 minutes then turned off again. so this time i replaced the flyback transformer and the horizontal output transistor the tv came on but the pichure was pulsing and wavie it was working like this for 20 minutes then shut down and would not come back on again until i put a new horizontal output transistor back in then the same thing happend can anyone tell me how to fix this.