[miniman82]

Mitsubishi WD-65735 ballast no-power situation.

Yep, it finally happened. The Mitsu 65" is dead, and I might be in for a rather hefty parts bill unless someone has a better idea.

Just put a third bulb in the set, I've had it for 5 years. It's on most of the day, so that's why I went through so many bulbs. Only 2 weeks after new bulb #3 went in, I come home from work and the wife says TV is broke. Sure enough, no light out the back. I figure the new bulb went out, but it's fine. Troubleshot it down to some sort of issue with the main board underneath the power supply.

Here's what I have so far:

There is a pin labeled 'lamp relay' on the power supply board, which receives around 3 volts DC from the main board when the lamp is (supposed to be) on. 3 volts goes to a discrete transistor driver circuit, which then activates the relays for the lamp ballast. It's the same exact circuit for mains input, only mains has a single relay. So I make the assumption that the ballast is not being told to turn on, and jumper 'main relay' to 'lamp relay' on the power supply. Kills the whole set, there's a short somewhere in the lamp circuit so that any time I jumper it the mains relay goes open. I removed the lamp relay wire from its connector on the power supply side and tried again, light comes on no problem when I jumper it. I assume this means the main board is bad ($400, f that), or it thinks there is a fault in the lamp so it is off for a reason...

I don't feel safe leaving it jumpered, because if there is an overheat condition I could be setting myself up for a fire. So what's my best shot at fixing this, besides the uber expensive main board replacement? Should I try a ballast board first, on the off chance the fault lies there?