I swapped the two parts today, unfortunately without success. U2 gets super hot and on the 3.3 V line there is only 1.6 V present. @dc42 Could any other component pull the cable to ground or is it most likely a microcontroller?

@antunisac To exchange the components you need a SMD soldering station and some experience. Often there are open electrical laboratories at universities which are run by students who like to help. Good mobile phone repair shops should also have such a thing or small electrical specialist dealers. I think that would be a good start ...

I'm still waiting for a new U11 chip because I bought the wrong size. I hope it will come this week, after that I will hopefully be able to report on my successes.

Are you sure U11 didn't burn out, too?

@dc42 said in Short circuit of fan P0 and P2:

Was your fan voltage selector jumper set to the VIN position or the 5V position?

No, the jumper is on V_in. If I think about it, I probably short-circuited the 5 V pin with a fan pin. That would also explain why the diodes didn't burn out and the sparks on the measurement tip.

Can you still communicate with the Duet through the USB port?

No unfortunately not, the board is not recognized.

U2 is the 3.3V regulator. If U2 and U11 fail, this usually means that there has been excessive voltage on the 5V rail. This may in turn lead to excessive voltage on the 3.3v rail. However, if the green 3.3V LED is lit, that is a good sign.

After looking again, all LEDs except the 3.3 V are lit. This also explains why the board is not recognized by the USB.
I already ordered replacements for U2 and U11, they should come the next days.

If I have short-circuited the 5 V line with the 24 Volt, my odds probably are bad

My pwm fan didn't work anymore, so I measured the voltages on P1-3. Of course I slipped and short-circuited P3, with everything that goes with it: sparks on the pins and a magic smoke.

It looks like U11 (74HCT02) is burned as well as TR1&TR5 and U2 look strange. What worries me is that the U11 is completely switched through and the extruder and heating bed are supplied with full voltage. I don't think that should happen.

I will replace the parts and see if it works again afterwards. Could the microcontroller break in case of a short circuit on P3.
What should happen if there is a short circuit at a fan pin? Diode D18 and D21 are not broken and have a voltage drop of 0.5 Volt.

Stupid mistake of mine, wouldn't want to get a new board. So I'm grateful for any help. If not, it seems Duet 3 is coming out soon

Edit: - When I apply voltage, all LEDs on are only the wifi module does not light up (connection LED).
- Duet Wifi