If your main fan is not turning or not turning reliably, most
likely your fan controller on the main board has failed. I don't
have any information on the voltage requirements for the fans.
The service manuals for the Infocus projectors does not have any
schematics so I wouldn't know where to pull power from without harming
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Fans have 3 wires, power (red), ground (black) and third is RPM. If the fans internal RPM sensor isn't providing the speed reading to the electronics it thinks the fan stopped initiating an error shutdown process. You could possibly try an outboarded fan with the same wiring and voltage to see if that makes any change but if replacing the fan with an OEM fan doesn't fix it, then you have a board issue or wiring failure if the fan doesn't plug directly into the board.
The fan is a brushless fan and very reliable but they do go wrong check to see if you have the supply to the fan assembly there are usually three wires two are the supply the other is the speed control wire tacho run the fan on a separate supply and see if the fan runs before you start checking the voltage on the mother board first.The most common fan for failure is the exhaust fan or heat output fan because it is always mounted near the lamp assembly and bearings do not like heat
Its been along time since I worked an LP70. But if you can remove the top cover, look to see if there a green wire soldered directly to the main board on a yellow/orangish block looking thing and then leading to the underside of the power supply. If you see this then the ground upgrade was done to this unit. If you have a black cable screwed to the top of the main board or nothing at all then it will need the modification or a new power supply. Also if any of the fans are not working this will cause premature shutdown. Sometimes if the top is not put on properly it will push down on the plastic surrounding the double fan and will cause the unit to shut down because the fan can't spin. The best way to determine a ground vs. a fan issue is to test the unit with the top off. If you see the fans are running and it shuts down then it is likely a ground issue. If you do in fact see that the unit has had the upgrade and runs fine with the top off, before you put the top back on break off the 3 fins inside the underside of the top and make sure the dual fan cable is routed properly thru the little slot in the top of the fan housing. Good luck.
before buying a replacement part try to check first if there is wire touching the fan. Probably there is wire that was accidentally trip and touching the cooling fan. cooling fan didnt break so easily so check it first before buying a new one.
Here's the fix: Take off the top cover of the projector. Unplug the
wire leading from the two fans in the back of the unit to one of the
circuit boards in front of you. Just trace one wire from fan to board.
Unplug at board. Turn unit on and it will again turn on, show HP splash
screen and then shut down, like it should, because the fans are now
disabled. After it completly shuts down, plug the fan wire back into
the board. Turn the unit back on and, presto, its working again. It
will not turn off.
Not sure if this helps with the 7200 bu had a 4805 with a failed fan issue. There are two fans inthe unit, one smaller one that cools the color (colour) wheel and the larger one that cools the lamp. This unit had a problem with the larger lamp fan not turning. Unplugged and disassembled the unit to get the fan out and tested the fan using a 9v battery and a couple of wires (best to uplug the fan from the controller board so you are not forcing voltage into the unpowered controller board... that said, I did it hooked up just peeling back the label in the centre of the fan and touching the wires to the solder contacts) The fan worked fine so figured the controller board was the issue, so this wasn't going to be a simple "buy a new fan" issue.
Here is where your mileage may vary...
I decided that it would be OK to just run the fan. Unplugged the fan and powered it from the 9V battery and assembled the unit and powered it up. Found that there was 7v available on the power board at the second pin that was alwasy on when the power switch was on (thats the positive 7 V pin, but measure it with a meter since we are talking about a different projector) and just wired the fan direct to pin 1 and 2 (1 is ground on the 4805, 2 is +7V) and so now whenever the main power is on the fan runs, so after ti cools down I just power off the main power when not in use... or let the fan run if the noise isn't an issue. Crude but effective fix.
Thank you for your email inquiry. It appears you are looking for the light tunnel for a projector? My intial question to you is why are you seeking the light tunnel to your projector? also, which model is it?