Here is the solution. I have this same tv and the same thing happened to it. I spent a lot of time searching on the internet for a fix. I finally came across one. Basically there are two capacitors on the main power board in the tv that go bad. You can tell because the tops of them bulge. I bought new ones on the internet for $6 delivered. I figured it was worth $6 to try this solution that I had found. If it did not work I was only out $6. I am not a professional repairman or anything either. I do know how to take things apart and have done some basic soldering in the past. So I ordered the capacitors specified below and took my tv apart. Just as the instructions said I had two capacitors right next to each other that were bulged. I carefully removed the board from the tv and then got out my soldering iron. I removed the two capacitors after watching some how to videos on youtube. Then I replaced them with the new ones and put everything back together. Turned on the tv and it has been perfect since. That was about 4 months ago. People that tell you that you need a new board are technically correct as this would fix your problem. But this is what is wrong with the board. It really is a $6 fix.These two capacitors just need to be replaced. Below are the exact instructions that I followed. If you have questions you can email me at firstname.lastname@example.org
HERE IS THE FIX:
1. Unplug your power supply cord.
2. Remove back panel on your HD.
3. Look for capacitors that have a bubbled or slightly raised and rounded top. This indicates the capacitors have overheated or leaked and need replaced. The normal look is a flat surface with no raised feature at all. (I had two bad capacitors that were side-by-side and identical: 3300uf 10v. Also, they should be located on the power supply board. My power supply board was in the middle of my 50" plasma.)
4. Go to an electronics store or Radio Shack and see if they carry your capacitor type and size and replace them yourself if you are comfortable with removing the capacitors and soldering new ones to the power supply board. The capacitors will cost you $2.00 each or less.
5. I was not comfortable replacing the capacitors myself so I removed the power supply board by removing the screws and unplugging several wire connections. This was not difficult at all. I then brought the power supply board to a local electronics shop that did repairs on HDTVs and simply asked them to solder the two new capacitors onto the power supply board. They did it for FREE while I waited and it only took about 10 minutes.
6. I replaced the power supply board and back panel of TV and it worked!!!
Some people on this sight suggested replacing the capacitors with some that have higher temperature ratings. Based on that advice, I wanted to replace my two that were bad (3300uf 10v) with two rated at 4700uf 35v, but my electronics guy suggested against it. Instead, I replaced mine with 3300uf 16v, with the only difference from the original parts being the higher voltage (16v instead of 10v). I figure if the problem occurs again, I now know I can get it fixed for less than $5.00. Philips - Magnavox should be ashamed for such poor customer service and not telling people about this simple fix. When I called their customer service support number I was simply directed to a repair place -- two hours away!!!