While working on my project I supplied 12v to my pro mini through raw input and then a s4 named component smoked and my pro mini stopped working . It didn't turn on either through vcc or raw. The voltage regulator seems completely fine. Can I repair my pro mini. Please help. enter image description here

  • S4 is most likely a Schottky diode. You could try replacing it (in the correct orientation) and hope nothing else is damaged. Don’t run it at 12V in the future I guess. The fact that it doesn’t start up with just Vcc is not a good sign but you might have to remove S4 from the board first. Do you have a data sheet or schematic of your particular Pro Mini clone? Is it a 3.3V or 5V version?
    – StarCat
    Commented Apr 20, 2021 at 6:24
  • Sorry but i can only tell you that it's a 5 v version. Commented Apr 21, 2021 at 2:15
  • How do you konw if the voltage regulator is completely fine? Is that purely based on visual inspection or have you tested it? Since the failure, is it regulating the voltage to 5V (measured with a multi-meter)?
    – sa_leinad
    Commented Apr 29, 2021 at 2:21

2 Answers 2


Many Arduinos have a Schottky diode between the power connector and the voltage regulator as a protection against accidental reverse polarity connection. The official Pro Mini, or the Sparkfun variant, does not.

So you can either de-solder the diode or break it off the board using diagonal cutters and then replace it with either a similar diode -- or with a solder-bridge if you are confident about never connecting power the wrong way around.

It's possible (likely even) that other components that look OK visually are actually damaged. Especially if you can't power the board by connecting a regulated 5V supply to the VCC pin.


Once you have removed the diode as described in @RedGrittyBrick's answer, you will need to replace it with another. Note you don't have to replace it with a SMD version if you can't get your hands on one. Most electronics shops sell a 1N4004 or 1N4007 diode which would be a suitable replacement.

If worst comes to worst, you could solder a blob of solder across the diode's pads - which would mean you lose the reverse polarit protection - but it would provide a path for your voltage input to go into the regulator.

  • The defective component is a Schottky diode. 4001 or 4007 are not Schottky diodes and have much higher Vf. A better replacement would be 1N5817 or an SMD equivalent.
    – StarCat
    Commented Apr 29, 2021 at 9:23
  • It doesn't matter in this instance as it is just for reverse polarity. A normal diode is fine, a Schottky diode would be better if you can get one.
    – sa_leinad
    Commented Apr 29, 2021 at 14:35

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