I haven't worked on that specific model, but on my PDP-V501X (much older model, but still a Pioneer), on a cold startup, the fans kick on after a couple minutes of the initial power up, and run continually until the set is powered down. Subsequent startups with the set warmed up, the fans start with the TV. I don't think you'd have any harm in just having the fan run all the time.
I know that doesn't help with the "real" problem, but I figured I would throw that out there
