I have a 55" Toshiba

I have a 55" Toshiba Rear Projection TV and it works great for 30 minutes or so and then it just turns off. The picture is prefect as is the color...Then will not turn back on again, just flashes a red light..If I unplug for several hours and then plug it in and turn it on, it will possibly work for another hour or so....I called a Toshiba recommended repair technican and he came and took the electronics out and supposedly repaired the unit, believe he said it was probably the convergence problem, nad that he did not need to take the whole set...Well he repaired the unit and just recently replaced the repaired chassie and if anything it is worse now than before...the unit came on and turned off again this time after 1 minute or so...then the lights flash red...He wants to take the whole TV now to his shop to repair it..estimates are $400+ Any suggestions as to what I should do??? Is the unit, which is 10 years old worth repairing?? We were O.K. with the $400 estimate but now am worried that it is a scam. He saids that he will repair but that I will only get another 2-3 years out of it anyway..Bob Boutin