Fan0 fixed at 2.56v

  • I'm unable to get my blower fan working. The extruder fan works, and is connected to always on, but no matter what I connect to fan0, it won't budge. I've tried multiple fans, cables and connectors.

    No matter what speed I set it at on the control panel, or what M106 command I send, fan0 is always at 2.56v. The fan1 and fan2 connectors at stuck at 1.6v.

  • administrators

    Fan1 defaults to thermostatic mode, so you need to disable that to control it directly.

    How are you measuring the voltage: between the two pins of the fan connector, or between a pin and ground? Either way, be very careful: if you short the two pins together, you will blow the associated mosfet.

  • See, that’s what I’m thinking I did. When the fan wasn’t working, I accidentally shorted the two pins with a probe briefly. Does that mean none of the PWM fan connectors can work now?

  • administrators

    If you short the 2 pins of a fan connector together, usually just the mosfet driving that fan blows. However, it's possible that you have fused a trace that supplies VFAN to all of them. If that's the case, the trace can be bypassed. To find out, measure the voltage between the VFAN pin of each fan connector and ground. It should be VIN or 5V depending on how you have the V_FAN jumper set.

  • Crap. I’ll tear into it when I get home. I noticed on the schematics the fan1 mosfet does not have a resistor where fan0 and fan2 do. Why is fan1 different?

  • administrators

    Fan 1 defaults to being on at power up, because it is typically used for the hot end fan. You wouldn't want it to be off if you decided to flash new firmware while the hot end was still hot. The other two fans default to off, hence the pulldown resistor to defeat the pullup resistor in the microcontroller.

  • Ah. I see.

    So I remembered how the webUI would go down during a print and wouldn't come back up until the print finishes or a failure stops it. I doubt it, but maybe it's corruption. So I erased the SD card and made it up all over again. I also put the extruder fan on fan0 and the filament fan on fan1.

    When I turned on the machine, the Fan1 spun up, then turned off. So we know that one works. Fan0 is still sitting there, silent. Fan2 doesn't do anything either. I'm going to poke around some more.

    Okay, after wiping and refreshing (everything. It got ugly as I stumbled around) the other fan connectors work fine. It looks like I did blow a mosfet. My soldering skills are shit though. I can make little arduino clocks and put headers on a raspberry pi, but I don't think I can fix surface mount stuff. Is this something I can bypass somehow or should I just us the other connectors?

  • administrators

    Removing the old mosfet without damaging the PCB is difficult without hot air desoldering equipment. Easiest is to use the other connectors. Forum user W3DRK offers a repair service in the US.

  • Fortunately I have unused connectors. Thanks.

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