Arduino Nano sort circuited-now dead. Is it the Scottky diode

Development Tools IDE 1.x
1

I know I am stupid but I shortcircuited the +5V and GND line on my Nano. My eyes are not that great anymore so I made a wrong connection on my breadboard.
Anyway, ever since, my computer does not recognize it anymore.
In an old thread (http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1256229321 ) I came across some people who had this problem as well and usually it is the Scottky diode that connects the Vusb with the 5V line: replace that and yr problems are solved.

Before I do that however, I had a few doubts and I was wondering if some people can maybe think along and give me some pointers.

  • I measured (with a MM) the diode and it still seems to have a low impedance in conduction direction and a high impedance the other way, like one wld expect with an intact diode
  • Nevertheless if I connect the USB, I measure 3 volts on the 5 V line (That line is directly connected to the kathode of the diode) and indeed 5V on the anode of that diode (which is connected to the USB supply line). 2Volts over a Scottky diode ofcourse is not OK.[\li]
  • Power led is still working, the Tx and Rx diodes only briefly blink at power up

Just to be sure I tried it on a different computer, the same problem.

So I actually had 3 questions:
Is it indeed possible that a diode 'blows' in a way that it still lets through current but obviously with a much bigger loss in Voltage? I thought that if a diode blew it wld either let all current through or nothing at all anymore.
If it is the diode, how critical is it to replace it with exactly the same one. Wouldn't basically any Scottky diode be OK?
Could it be anything else?

If this was all normal size, I wld have tried already, but with 50 yr old eyes and SMD, that is not something I look forward to.

Just to be complete (in case someone else is looking for a solution), I add a link to a picture of the underside of the board:
dead nano v3 | killed two in the past month with brief short… | Flickr (hoover over the picture to see a note on the diode)
and here is the schematic of the Arduino nano:
http://arduino.cc/en/uploads/Main/ArduinoNano30Schematic.pdf

My arduino does not look like that at all (a clone): In my case the diode is closer to the USB port, but as there only is one diode on the board, it should not be hard to find.

Your input is appreciated

2

Applying 5V to Vin gave me a functioning Nano again, so I guess the culprit is clear. Remains the question if it specifically has to be the MBR0520 Scottky diode or that 'any' other Skottky would do as well ('any' = 'within reason', sort of comparable)

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I toasted the schottky on my first Nano, too.
Mine didn't go open circuit (like yours), but it didn't work as a diode anymore after that; resistive, it still kind of worked.
I got replacements from Digikey, waiting to put together a list of other needs.
MBR0520LT1GOSCT-ND
If you're good and you can shoehorn something else in, then more power to you (so to say). If you put in a more resilient device, then it'll take more punishment, but that may result in more damage instead to your board and all down the line with any.. repeat performance.

4

Thanks. Yes, I thought about putting something more rsilient in it. at the other hand, now it sort of works like a fuse, a difficult to replace fuse.
I figure that a short with a more resilient device first and foremost cld lead to damage on the USB port. Maybe it is worth constructing a USB cable with a proper fuse.