Did I Brick my Arduino Pro Mini?

Using Arduino General Electronics
1

The Pro mini is now showing dead short to ground on the VCC pin... Is this a common failure mode?

I've been working for some time with an Arduino Pro Mini to run a stepper motor. The circuit has been built on a 2x2 solder-proto board, and all as been working well. I realized I was overpowering the LM7805 by putting 24 volts into it (from stepper supply) - dumping 19 volts makes for maybe 3 or 4 watts to get rid of... a bit much!

So went to a 12vdc wall-wart to provide the input to the 7805 - all seemed to go well but in the process of powering up the new setup, I noticed the 7805 was VERY hot! Didn't make sense, so began tracing all lines (with 4x MagEyes to view details) and found that after removing all wiring from the 7805 and the VCC lines on the board - the VCC pin on the Pro mini still shows a short to ground. I'm clipping the black lead of the ohm-meter to the heatsink of the 7805 - access to the boards ground system - and the VCC pin on the header is showing dead short... Did I brick the little sucker??? =(

Can't find any solder bridges or other bad wring - and it has been working for several weeks. It would seem something I've done in installing the new 12vdc supply has done... something... but not sure what!

=Alan R.

2

Dead short? Did you measure the resistance? Metal-to-metal shorts tend to be well
below 1 ohm, melted semiconductor somewhat higher.

First do a careful visual inspection - only takes one little stray piece of metal wire
in the wrong place to short things out.

3

As posted - went over the entire board with 4x MagEye head-mount magnifying glasses and found no bridges or mis-wiring. Reading resistance with my old Micronta digital meter shows .2 ohms when shorting the test leads together and also shows .2 ohms when I read from ground to the VCC pin of the Pro mini... I'd say it is toast! :roll_eyes:

=A.

4

My Pro Mini has 125k Ohms from Vcc to GND.

It's dead. Take it outside and give it a decent burial.

5

Yep!! Snipped off all connections to the back of the board and the short to VCC went away. Then I plugged in the FTDI board and plugged in the USB: INSTANT smoke and glowing spot in the center of the Arduino - with, no less appropriate curls of smoke!
=( Sigh.

Not sure how I toasted it - I'm not a noob-builder... but s**t does happen.

=A.