Duet fried?

As you can see in my other thread I am expanding my RMax with an autoshutdown and thermal fuses. Now a second problem has risen. When is switch on power the board does not light up and no fans are blowing (I have 2 fans directly on the 12V circuit) I hear a ticking sound, looks like my 12V stepdown is clipping. I am measuring 20V to the 12 V stepdown, but 0V on the 12V side of the stepdown. When I disconnect the board from the 12V line, the fans blow normally, and I get 12.5V out of the stepdown. So something must have happened to the board. The only thing I did was soldering three pins on the 5V, PS_ON and GND. I am measuring max resistancebetween all of those pins, so there is no short. Also I am getting max resistance on the Vin connector. When I connect a USB charger the board boots normally and I can get into the WebGUI (I have no paneldue).

What could be wrong and how do I go about testing that?

Are you sure that you have the + and - wires to the VIN terminal block the right way round?

Try disconnecting all heaters, motors and fans from the Duet and see whether the converter still fails to run.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Ooh, looking at the picture of the duet I posted in my other thread (about the PS_ON thing) I am not so sure I have my + and - wires correct indeed. I was so sure that I put them back the way they came out that I did not even check that, but now I see on the wiring diagram the red wire in the upper screw terminal, and the black in the lower. I am pretty sure I have them wrong then. I will have to check when I'm home. Will there be damage to the Duet?

I am pretty proud with all that I have accomplished and learned from tinkering with my printer, especially since I have no electronics background AT ALL. But these moments confront me with the noob that I really am