I accidentally connected 12V to PIN #2 Vin and let the smoke out of my MBed. The Mbed appears to be fried and does not power up when power is applied to Pin#2 or when connected to the USB port of my computer.

None of the components on the Mbed look fried to the naked eye but smoke definitely came out of something on the board.

I'm hoping that I just damaged the internal voltage regulator or something.

Does anyone have any suggestions? Like take off the voltage regulator and apply 3v from and external power supply, just to test if the Mbed could be fixed with a new regulator? I have no idea which component is the regulator though...

Thanks.

If you look closely at the top left hand corner, you should see a diode, the fourth component down, just above the 3.3 volt regulator. if this looks like it has exploded, then you might bee OK, but if the MBED is not powering up from USB. then aftre a look at the circuit diagram, if you mannaged to touch pin 3 with 12 Volts, then you have Killed the LPC1768, as this goes strait into the micro.

Just try holding reset down, then connecting to PC, KEEPING RESET DOWN AT ALL TIMES, you might be able to get the MAGIC chip, not that this helps, but you might be able to replace the micro, if you are super brave.

Cheers CERI

The diode above the 3.3v regulator does not look blown out. I guess I could remove it from the board and put a jumper across the pads to see if that is the issue.

After some further investigations....

The Mbed seems to work if I power it with 5V at Pin#2 Vin. I can download code to it through the USB cable and code seems to execute fine (only if I am applying 5V to Pin#2).

However, the MBed wont power up from the USB plug. Does that mean that Voltage Regulator IC3 FPF2123 is fried? http://mbed.org/media/uploads/chris/mbed-005.1.pdf

You should be able to determine which component is toast, with a goo DMM. At least it was not the processor :)

Enjoy

Ceri

Can someone from the mbed team help confirm which component on my board is fried?

Here is what happened. On accident I applied 13V to Pin#2. The device no longer powers up when it is connected to the USB port of the PC. However, it does power up, download code and seems to run OK if powered with 5V on Pin#2.

I think IC3 FPF2123 may be fried bases on some testing I have done. I am assuming that IC3 is the the 5 pin deice on the top of the board between the VIN pin and the USB connector. I hope this is correct.

Test#1) With the Mbed1768 connected to the USB cable (no power to VIN pin) here are the voltages on IC3 FPF2123 as follows:

Pin1: 5.0v

Pin2: 0 v

Pin3: 5.0v

Pin4: 3.0v

Pin5: 2.8v

Test#2) With MBed1768 device only connected to the USB Port (no power to VIN pin): The Mbed device does NOT operate. The voltages on the MBed pins are as follows:

VOUT = 1.9V

VU = 2.9V

VIN = 2.9V

nR = 1.9V

Test#3) With MBed1768 device only connected to 5V at pin VIN: The Mbed Device DOES operate correctly. The voltages on the MBed pins are as follows:

VOUT = 3.3V

VU = 0.25V

VIN = 5.0V (input voltage)

nR = 3.3V

Any help would be greatly appreciated.

Thanks you!

I would sudjest lifting D1,

test the voltage, on the Annode's pad, (or pin 5 of IC3) if this is still below 4.5 volts,

you could try tacking a wire from pin 1/3, to the VIn Pin and measure the voltage on the O/P of IC4 & 5.

If so then there is a good chance it is the FPF2123, which is avalable from Farnell for £1.11

OR if you want to be a bit wrecless, remove IC3, and fit a low value resistor 10 Ohms (or a big blob of solder) in R13 place.

Hope this gets you going :)

Cheers Ceri.

Hi Freddie,

Sorry to hear you are having trouble. I assume you've had a look at the schematics of the mbed Microcontroller, which are available at :

http://mbed.org/media/uploads/chris/mbed-005.1.pdf

If the FPF2123 were fried I'd expect it to still work when powered from VIN, and still be able to download code over USB. The functionality that would be missing is the ability to power from USB and of course the 5v supply from VU. In this respect it does sound like the FPF2123 is fried.

The part that I don't quite understand yet is how the FPF2123 was fried. Connecting 12v to the VIN pin certainly shouldn't do that. Referring to the schematics, you'll see that VIN is routed into the LD1117S33 regulators. Although the pin out card suggests the maximum voltage is 9.0v, this was for thermal reasons (see http://mbed.org/forum/mbed/topic/127/?page=1#comment-1273). In light of this 12v applied to Vin shouldn't cause any problems, and certainly not to the FPF2123.

So in summary, it does sound like your FPF2123 is fried from what you have described, but it is not clear how this would have happened from applying 12v to Vin.

Ceri has made some suggestions on how to repair your mbed - I'd always be inclined to suggest replacing the FPF2123 as this will offer some protection to your computers host interface.

Best regards, Chris

The pinout card that came with my mbed suggests that you can put anything between 4.5V and 14.0V on pin 2 (VIN). Is that wrong then?

It is possible to put in a higher voltage, but being a linear regulator, it will produce heat. Which semiconductors don't like ;)

Enjoy Ceri.

I have just downloaded the datasheet, for IC3, and the ABSOLUTE Max input voltage is 6 volts. I am guessing this is the cause of it's demise :(

Ceri.

Just a correction, if you're using a LPC1768 mbed then the voltages mentioned are 4.5-9.0v (http://mbed.org/handbook/mbed-NXP-LPC1768).

My bad. I ment VUSB, Pin, (from PC) Thru USB cable.

Thanks for the help guys! It is much appreciated.

Is the R13 resistor a current limiting resistor that could be used instead of IC3? Why is the pad for R13 even there? Is it just to provide protection for the host PC? If yes, then why would you ever not want to have IC3 present?

I just ordered a FPF2123 from digikey http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=FPF2123TR-ND. I also ordered another mbed.

Now I just need to practice my soldering skills and be more careful hooking up voltages next time!

HI Freddie,

The footprint for R13 was there for experimentation. I had originally looked to use a fast trip polyfuse in an SMD package instead of the FPF2123. At the time we went to production the FPF2123 based design was tried and tested, and so the the incentive to move to using a polyfuse was low.

So the R13 pads are there as a production option, giving us the ability to build with FPF2123 OR and SMD polyfuse.

Hope that clarifies!

Thanks Chris