So I am having some problems with my home theater projector. I am using an oscilloscope to attempt to verify the fans are all working correctly but I am a bit confused by what I am seeing. I was under the impression that fan tach outputs were a square wave equal to the fans input voltage, but having tested all 5 of the fans in this thing that's not quite what I am seeing. The only one that is "different" is this one: Compare that to this one which is more or less what the other four fans look like: Is the fan in question bad? Would that extra "dip" be enough to make the control board think the fan has failed and shut the unit down?
I don't think it's anything to worry about - the signal from the tach is a noisy signal and not designed for accuracy; to see a slightly garbled signal like that is nothing out of the ordinary. What are the fans, and do they all power up at the right voltage?
The fans are in my home theater projector. I tested all 5 fans by applying 12v from an external power supply and they all spin up like they should. The projector itself I think uses voltage regulation to control fan speeds since they don't always spin at full speed, but are only 3 wire fans. Thusly, I don't know what the actual startup voltage is. The projector has taken to shutting itself down after a few seconds of operation. I was hoping it would be something as simple as a bad fan but all the fans and their tach outputs seem to be working...
Have you cleaned all of the filters and made sure that the temp sensor and lamp is okay? A bad temp sensor would make the projector shut down quickly as it would think it was overheating.
The only temp. sensor I can find inside this thing is a mechanical on/off unit mounted under the bulb. I have continuity through it and when the unit is failing the temp. warning light does not illuminate. The filters are clean and the bulb probably has less than 200 hours on it. I also tried my spare bulb which has unknown hours but I know is good. The only difference between the newer and older bulbs is with the newer bulb, the bulb never illuminates. With the older bulb it starts to light for a few seconds then turns back off. It doesn't stay on long enough to get warm enough to put any light out of the front of the projector. I am looking in through the grill in the back directly at the lamp. After the projector shuts down it runs the fans at full speed for 10 seconds or so then resets and is ready to try again.
Well it appears that my new lamp is kaput. The last few days the projector wouldn't fire up with either my new (sub 200 hours) lamp or the old spare lamp I had laying around. Today it fired up and ran fine on the old lamp but would exhibit the above symptoms with the newer lamp. I swapped the lamps back and forth a few times to make sure the result was duplicable and each time the new lamp failed. We finally got to finish the 4th Harry Potter movie and watch the whole of Prometheus on the old lamp. I'm glad it turned out to be an easy fix. Thanks to those who chimed in. As a reward for your efforts, have some projector porn (forgive the graininess. All I own is a point-and-shoot cam) : Guess that'll teach me to buy a made-in-China knock-off lamp
