I did the exact same thing on my toshiba 42" (I was wrong earlier, it's not 46" it's 42 lol) but it took about 6 years for it's IC chips to go out. I had to do a whole bunch of research, and then I bought 2 new chips off the internet for around $27. I pulled the board and yanked the old ones, then soldered in the new ones. Then I spent about 2 hours calibrating it just to get the picture to look right again. But it worked, and I saved myself a $500 repair fee.
However, after doing the research on the problem, I think I may have come up with a solution, one that might even help you with your mitsubishi. Ever thought of putting some little heatsinks and fans on the IC's? I don't mean some regular ol' heatsinks, but instead use some aftermarket ones for a PC. Many of them cool very very well. I know this from my overclocking hobby. If they can cool a CPU from a computer that is running 3.4Ghz (when it is only supposed to be running 1.8Ghz) then I think that they should have no problem at all cooling some IC chips. You could even put a little delay in line of the fan, to have the fans not come on till the chips had a chance to warm up. Then without all the heat, the chips couldn't die.