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My new oscilloscope arrived today and thought I'd play around with the ESP32 to see what signals I could get out of it. Unfortunately, being a cack handed imbecile, I think I shorted GND to Vin (or possibly 3V3 - either way, the GND pins are directly next to the voltage pins). Now when I connect the USB cable, no lights come on and measuring the voltage with my DMM gives about 2.1V on Vin and 1.2V on 3V3. By putting it in a breadboard and connecting the 3V3 pin to a working ESP32, it powers up (and from what I can tell seems to function correctly) but I can't upload any new sketches to it via USB.

There is a diode on the board that on the good ESP32 measures 0.23V across it (with DMM diode setting). On the "bad" ESP32, the same measurement is 0.61V (but still open circuit with the leads reversed). I tried this after reading:

https://forum.arduino.cc/t/esp32-failure-and-repair/655168

ESP32 diode position

Is there anything else I can try before attempting to replace components?

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No you have the general idea down already. These boards typically have a reverse protection diode, a fuse, and a regulator in the path. When you short it any of those can go. And if you short a gpio the microcontroller can as well. The passive components to the regulator are another possibility but less so.

If you can bypass the regulator by inputting 3.3V at the 3.3V pin and it works, then the issue is up stream. If you can put 5V into the VIN pin, which typically bypassed the diode and or fuse, then the issue is likely the fuse and or diode.

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  • \$\begingroup\$ The fact I get different voltages from the regulator implies (to me at least) that it isn't fried. I have tried powering this one by putting 3.3V to the 3V3 pin (from another working unit) and it works - can upload to it too so microcontroller appears to be working. In this scenario, your implication is that the issue is "up stream" - can you elaborate, please? I can't see a fuse on the schematic but I'll have a good look. \$\endgroup\$ Commented Oct 14, 2021 at 16:59
  • \$\begingroup\$ Upstream being between the power input and the microcontroller. As in the diode and 3.3V regulator. Your board may not have a fuse and uses the diode as the fuse kinda. Cost cutting. And yeah if your getting different voltages from the regulator output, it may be damaged. But if your not seeing a normal drop across the diode, that means the regulator is not getting a proper input. \$\endgroup\$ Commented Oct 15, 2021 at 3:37
  • \$\begingroup\$ I'll try replacing the diode first then look at replacing the regulator. I think I tried powering it by putting 5V to the Vin pin and it worked - diodes on order anyway. Hoping I can fix a few more things I've blown up! \$\endgroup\$ Commented Oct 15, 2021 at 7:02
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it's a little late, but I've also blown the same USB +5V input diode on a few of my ESP32 Devkits. The diode is only used for reverse polarity protection. It's rated at 100mA so it's esentially a fuse. THe board will work just fine by replacing the diode with a jumper. Reverse polarity protection on USB signals is really not needed sice the connectors at either end of the USB cable can be incorrectly inserted. Hope this helps others who have blown these diodes on their Devkit boards.

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