While waiting for a replacement board I decided to do a little more redesign of the system. Currently the mainboard cooling fan is a 24-volt fan, and the two fans on the extruder for the heat break and part cooling are both 5-volt fans.

The SKR 3 has two sets of fans, Normally On fans which run at the power supplied to the mainboard, and CNC Fans that can be commanded on and off, which run at mainboard voltage or can be adjusted with additional hardware, but all CNC fans must run at the same voltage.

Here is the fan breakdown and how I want them powered:

40mm x 10mm Heat Break 5-Volts: Normally On

40mm x 10mm Part Colling 5-Volts: CNC

Case Fan 24-Volts: CNC

This is the worst possible configuration. The Normally On fan is too low of a voltage and the CNC fans don't agree on a voltage. I don't want to mess with buck converters or anything to change the voltages around.

The answer is to swap the two 40mm x 10mm fans for 24-volt versions and run all the fans at the native voltage of the system. Fewer parts, less complexity, and the fans are really old, so they could use a change out.

I'll have to enable the USE_CONTROLLER_FAN option in Marlin and configure that to one of the CNC pins. This will turn on the loud board fan only when a movement has been commanded and will automatically turn it off after a delay.

Technically I would be able to add the heat break to the CNC fans and have it only activate when the extruder is hot, but I have my 3D Printer in an enclosure, and I might want to use the third fan for the enclosure. As it is right now, the entire printer shuts down when the print is complete, which makes turning off the heat break fan redundant.

I've also ordered a new 24-volt power supply. The Lulzbot one is old, and while I have things taken to bits, I might as well replace it too. This leaves only the frame, extruder, and steppers from the original Taz in place. The Taz frame has always been its best feature.

More parts should appear this week.