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UM3 Front fan receiving low to no power


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Posted · UM3 Front fan receiving low to no power

I ran into an issue today that stumped me. The print core cooling fan stopped working today and I assumed I would have to replace it as I have before. But when I plug it into one of the part cooling fan ports it powers without issue. So I assume its not receiving enough power from the board?


Additionally when it is plugged into the correct port it doesn't start to spin on its own, but if I manually spin it it will continue to spin on its own power at an extremely low RPM which makes this a bit more confusing for me.


Thanks for any input you guys have!

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    Posted · UM3 Front fan receiving low to no power

    First realize the front fan only comes on when either core is above 60C (or 40C and a core is turned on).


    Here's the relevant part of the schematic of the UM3 print head circuit board.  All 3 circuits use the same electronics and all 3 put out 0V and 5V.


    I'm guessing Q1 has failed.  That part can get pretty hot.  I'd just order a new print head board.  Although if you are really good with surface mount soldering you could test the voltage at the base of Q1 (should be around 0V when fan is supposed to be off and around .7V when the fan is supposed to be on).  It could be that the emitter is broken (pin going to ground) and the fan is powered from the previous circuit through that 330 ohm resistor.  The fan gets 5V and 0V power separately from the other inputs (although maybe the fans don't use that second ground?)  Normally if things are working, when the fan is off the top of Q1 is about 5V and when the fan is on the top of Q1 is approximately 0.2V.



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