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  • Huh... First of all: thanks for looking into it. However, second of all, I don't understand how this is possible. i.sstatic.net/6NKYn.png This is exactly how my board looks like. Maybe there are different NodeMCU v3? In your schematic, shouldn't I measure 0 V on VIN because it's against the diode direction? But when I connect USB and measure from VIN to GND pins, I read 5 V. (I get 5 V as well from VU to GND, by the way.) Again, thanks for you help :) Commented Oct 5, 2021 at 13:24
  • The only way you can get power out of VIN is if the diode is faulty or installed backwards. That board is identical to the one I've torn down. I am half way through a full reverse engineering of the circuit at the moment. Commented Oct 5, 2021 at 14:42
  • Hmm, no idea what to tell you. The board is basically new, I haven't done anything with it so far. I also read 2 to 3 ohm resistance between VIN and VU in both directions. I think if there would be a diode installed like in your schematic, that also shouldn't be the case. I cannot explain my readings. Is there anything I can do? Which part would be the diode in question? Maybe I can test something there? My equipment is very limited though. :( Commented Oct 5, 2021 at 15:42
  • @rattlesnake If you have a DMM it should have a diode test mode. It should tell you the forward voltage of the diode. In one orientation it should give you abou 0.25V. In the other it should read open circuit. The diode in question is the one closest to the pins. If you're interested the copper traces can be viewed here: cloud.majenko.co.uk/index.php/s/ewCn6JmYdWWglRj The two diodes are in the bottom left - you can just make out the pads in silver above the bottom left mounting hole. You can see both the diodes connecting the power to the 5V rail - the lower one going right to left... Commented Oct 5, 2021 at 15:52
  • ...from the USB power, the upper going left to right from the VIN pin. From there the 5V goes to the input of the LM1117 voltage regulator. Commented Oct 5, 2021 at 15:53