My Optoma HD72 projector operates for about 1 minute and then shuts off. I kept my old bulb around "just in case", I've replaced the bulb with the old one and have the same problem.

The problem is not over-heating. The Optoma HD72 has a known problem that Optoma won't advertise. The lamp driver is faulty. They simply have to replace the lamp driver. I purchased a spare lamp with my original purchase. I had the exact same experience as you at around 1200 hours on the lamp in ECO mode. I used the spare lamp. Same thing happened at about 1200 hours. I had a friend at Optoma. he confided to me the problem. I sent it in and they replaced the lamp driver at no charge. I got another 800 hours out of the first lamp and am now using my second lamp and have about 600 hours on it. The pic quality is so good with this projector (used Digital Video Essentials to calibrate) that I'll just order a bare lamp or two and use the existing lamp housings when I need a new bulb.

That must be an overheating problem . If you are sure that you replaced the bulb correctly , then i would say that one of these parts [ Power transformer , or Fuse , or the whole Power PCB ] is hurt .

please rate !