Hotend fan fails self test on new MK4.  

Hotend fan fails self test on new MK4.

My new, factory assembled, Mk4 fails the fan self test for the hotend (heatbreak) fan. During the fan self test the hotend fan visibly and audibly ramps up and at the same time the LCD rpm readout also ramps up to 6000rpm yet it fails the test. In that sense I don't know what actually failed since the fan appears to work fine and the software seems to be talking to it fine which leads me to suspect a false positive for the test failure condition.

I chatted with support for about an hour (forgot to save the chat log) and the last thing we tried was setting the nozzle temp to 250C and watching the fan speed. The fan speed didn't change appreciably during the several minutes of the test (~2100rpm / 22%). The fact that the fan speed didn't ramp up whiled the nozzle was set to max lead them to conclude the fan may be bad and they are sending me another one. However, the heatbreak temp didn't go past 26C during the test which, to me, indicates the fan had no reason to ramp up. My thought is that the hot end didn't warm up much during the short test and the fan would not have been commanded to ramp up. I have not tried a longer test since I'm not sure about any of this and I don't want to damage the printer.

As for what 'I' could have done to the printer in-between factory assembly and the failed test. I built the Prusa enclosure and installed the printer into it which involved moving the power supply and removing the LCD from the printer and reattaching it to the enclosure (unplug/plug ribbon cable). Here is a link to an okay'ish vid of the printer performing and failing a fan test: https://drive.google.com/file/d/1hoVCYtG6x8cRBq0A6_GM3oNzc1nh_eA_/view?usp=drive_link