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While this board (listed on ebay as D1 Mini NodeMcu Lua WIFI ESP-12F ESP8266 WeMos 4M Bytes Development Board Kit) was powered by usb, I accidentially shorted between the gnd (G) and 5v pins on the left, and some magical smoke escaped.

I can no longer power the device from usb, but it works nicely if I supply it with the right voltage on either the 5V on the left or the 3V3 on the right.

So something has burned between the 5V on the usb and the 5V on the regulator. I have tried measuring the components with an ohmmeter, and compared it to a working board, but I can measure no difference.

Is one of these tiny components a fuse, or a diode to prevent backwards voltage from board to pc, if the board is powered on the pins?

Or could the short between 5V and GND have caused a track to burn?

D1 Mini

  • Hard to tell. Examine it closely with a magnifier and look for holes and cracks in components. There may be a diode there that has gone... – Majenko Feb 23 '18 at 0:41
  • Looking at a possible schematic, yes, there is a diode (called D2 on the schematic) that would likely blow if you shorted 5V to GND. – Majenko Feb 23 '18 at 0:42
  • Looks like it may be just left of the USB socket (small and black)... – Majenko Feb 23 '18 at 0:42
  • I think I may have a D1 Mini somewhere here. If I can find it I'll have a look at blowing it up (AKA "destructive testing") to see what happens. – Majenko Feb 23 '18 at 10:51
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    @adeelx Immediately to the left of the USB port is a ceramic capacitor. Directly above that is the diode. – Majenko Jul 6 '18 at 8:51
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Try measuring with a voltmeter to compare the good board to the bad one. If it is the diode as mentioned in the comments under the question, you should get a different reading on the bad board. It should be fairly easy to replace if you have a soldering iron and a steady hand.

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    Indeed; I measure about 0,4v across the diode at the good board and 2.9v at the bad board. I don't have SMD-diodes at hand, but I guess I'll solder a wire from the usb-end to plug into my breadboard while testing. – Lenne Feb 23 '18 at 11:49
  • @Lenne Did you figure out which diode needs replacing? I'm in the same condition and would like to salvage the board if possible. – adeelx Jul 6 '18 at 7:52
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I came here because of a dead Wemos D1 Mini Pro. One which I managed to kill in exactly the same way (shorting out something while trying to measure a voltage - most likely I shorted the 5V and GND as well :) ).

The symptoms were identical - could power the board via 5V or 3V3, but not via USB. And they were solved after replacing the diode - or, more accurately, bypassing it, since I was unable to find an SMD Schottky to replace it with.

I won't tell you the rest of the story (where I first blamed it on the voltage regulator and replaced that), to save myself the embarassment :)

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I can confirm that the component, which on my Mini clones (which have an almost identical layout) is the tiny black component pictured at the upper left corner of the USB shielding, is a diode and can be blown pretty easily by shorting +5 to Gnd. I did as you Lenne proposed and jumpered it with a tiny wire and recovered the device.

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