EMI Suppression bead

Had a bit of mishap with my mega 2560. I had a probe connected to the ground of the iscp1 connector which shorted against the reset pin then I saw the magic smoke. At the time I was doing some testing trying to get a stepper driver to work then after dis-connecting and re-connecting power the board doesnt work. The power led and pin 13 led are lit but nothing else, cant upload sketches or see the board on the comm port. At first I thought the short had burnt something out but then thinking about it connecting reset to ground is a normal thing to do for a short period of time anyway. Going over my board with a magnifying glass I found a component next to the USB port that appears to be burnt and its in the area where the smoke came from. Board was connected to a computer via USB at the time, so just to rub salt into the wound the computer doesnt work anymore either. I'm assuming its something to do with the stepper driver thats killed eveything. I identified the component from the eagle file board layout as an EMI suppression bead but the info on it is basic, L1 0805 BLM21 SMD EMI Suppression bead and thats it looking on the net there are loads of these with varying specs so does anyone know what is the right one.

I've got a new motherboard comming for the computer but it would be nice if the emi bead is the only thing wrong with the board.

It's just a little inductor; it's there to smooth out signals to the reset pin so it doesn't reset inadvertently. It's there as a precaution.

You can either jumper around it or it might be easier to replace it with a single-digit-ohm resistor if you have one.

Ouch, it sounds like something more than 5V got onto your Arduino board somehow - hence blown Arduino and motherboard.
I don't think grounding anything can do that sort of damage.

Your computer is fried and you're worried about your Arduino????

I guess the lesson is to stick a USB hub between the Arduion and the PC... Maybe I'd better get a hub!

I have a bad feeling your Arduino is dead... You can check the inductor with an ohmmeter (multimeter). It should read short (nearly zero ohms). You might also check the fuse F1 while you're at it. But that fuse and the bead only go to the USB port, so they shouldn't stop the CPU from running.

I'm assuming its something to do with the stepper driver thats killed eveything.

I assume so too... Motors put-out an inductive "kick" (high voltage) when turned-off suddenly. But, the motor driver should have protection diodes to prevent any damage (to the driver circuitry or the Arduino).

I assume the driver board runs off something like 12 or 24V? Normally, the circuitry on the driver board should prevent damaging voltage/current from getting-to the Arduino. But, if some semiconductor on the driver board fries and completely shorts-out, it's possible to get excessive voltage & current on the Arduino (depending on the driver design). Then maybe your ATmega chip shorts-out, putting excessive voltage out the USB port, frying your motherboard...

If you are paranoid, you might try optical isolation between the Arduion and motor driver (at least during the experimental/development phase).

Or, maybe your motherboard, or computer power supply, failed first, putting excessive voltage out the USB port and frying your arduino....

Connecting the reset pin to ground couldn't possibly cause that, it's a perfectly normal thing to do (eg. it happens every time you upload a sketch).

That for all the replies, I have had a go at jumping the EMI bead but got nothing from the arduino although the computer I was using did recognise it as a usb device then when I removed the link windows didnt recognise it so it part of the probelm, I'll have a look at the fuse next altohugh it says that it is supposed to reset when the fault is removed.

The computer was only an old netbook so no great loss but a loss all the same adds to the expense of failure/s