@buggy said in Duet 2 D0 Output to Extruder only 12V with 24V Power Input:
it is the "E0 HEATER" screw terminal on the board that goes to the Extruder. It only has the 12V output.
To use a common terminology, please refer to this connections scheme of the Duet 2. On top near left, you see the screw terminal labeled E0 HEATER. The terminal has two outputs: VIN (which is an output despite its name) and E0-. The color of VIN is orange, which, if you refer to the KEY table on the right, means V_IN (e.g. "input voltage"). E0- is orange/black, which means (according to the KEY table) PWM V_IN.
So, what can you expect to measure? If you feed your Duet2 with 24 volt, you should get exactly this voltage from VIN. To verify that, connect GND of your voltmeter to GND (see screw terminal POWER IN to the right) and probe VIN of the E0 HEATER.
Now to E0- of E0 HEATER. The colours tell us it’s a PWM signal. This means that pin E0- can be pulsed to GND by a MOSFet. This transistor is controlled by the Duet in order to feed the heater with the amount of current it needs to be kept at a certain temperature. Think of E0- as an electronically controlled valve.
This "valve" changes its voltage level depending on several conditions, for any measurements with a voltmeter it is sufficient to know that it pulses at a rate you can’t properly read with the multimeter. In short: it is meaningless to measure the voltage between VIN and E0- of E0 HEATER. It is useless to test E0- against GND or VIN as well: sometimes, you could read 24V (or 12V, doesn't matter), sometimes approx. GND. But it is almost impossible to determine when or why you should expect some or some other voltage. To trace a PWM signal, you need an oscilloscope.