Got my HPT4254 repaired here too
Seconded - my HPT4254 failed catastrophically after about 3 years, it turned itself off and on again, then the power supply blew up with a loud pop. There were scorch marks by MOSFET QX801 (see the blog link, above).
I found Preher-Tech by way of this page plus a few other references (e.g. http://www.electro-tech-online.com/repairing-electronics/112461-emergency-broken-samsung-42-plasma-hpt4254x-xaa.html). Sent the board to them for repair, and the set is working again. Their email service was great, and I thought the price was totally reasonable. Probably cheaper if you can do the work yourself, but they fixed the whole board for me (I saw that they replaced my QX802 as well, plus I think capacitors that are known to be prone to failure - the caps look new but I can't tell by the soldering work, it looks perfect). All I needed was a screwdriver + the gumption to swap out the board. Plus, if you look at their blog, they're helpful and offer advice to people who want to do the repair themselves.
So I can wholeheartedly recommened Preher Tech - sorry if this sounds like a pitch, I'm just a very satisfied customer - if you're looking at this page, anyway, it's likely that your Samsung set died a similar death, but these guys can fix the problem.
Also, as to the note below, I have not needed to make any adjustments after replacing the power supply. Just reassembled the set, turned it back on, and it's working great
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