I was using a breadboard and accidentally reversed the polarity on my servo and think it sent the 8v in the ground on my mbed. I was looking at http://mbed.org/forum/mbed/topic/127/ this but have only used and ac to dc adapter to put 5 volts into the mbed and it would not start. The VIN pin got really hot. When hooked up to usb here are the volt meter readings I got. Any tips, any ideas what I might need to replace? Thanks, Chris

GND to VOUT =.07V
GND to VU=.11V

Hold down the reset button and plug in the USB cable. Does the power led light up? Does the usb drive appear on PC?

Just tried that, the power led doesn't light up and it doesn't appear on the PC. Thanks for the suggestion.

Any other suggestions?

I got 618ohms across gnd and vout. Is it just the 2 regulators? I get low voltage across the regulators

http://mbed.org/projects/handbook/svn/MicrocontrollerTRM/mbed-005.1.pdf?format=raw

My first thought was that D1 was blown. But then I saw you that Vu(+5V) is before D1.

Try using external power to pin Vin. If that works replace IC3(FPF2123) and/or C10

Ya Vin doesn't work, but thanks for all the suggestions.

Dear Christian Lerche and all,

I just brought a Mbed module. Yesterday just received it but to day this module is dead. T_T

Vin is connected to 5V and the module is wire up with RJ45 Ethernet Magjack socket. After power is status LED is not turn ON. Then i measured the LD1117S33 regulator Vout just 1.27V only.

So, i tried unsolder the regulator out from the board and measure the Ohm's regulator Vout to GND. The measurement result is 1.2 Ohm, look like the LDO Vout is going to short to GND. After remove the regulator I do check the regulator Vout again. The Vout result is 3.3V.

Please kindly advice.

Hello Lerche,

Thanks for your reply.

Before that mbed is working when i testing Hello World sample code LED blinking, everything is working fine, the middle LED was turn on by that time. But now the middle LED is not light up any more, i through this middle LED is get the supply from the LDO which is near to pin-4 to pin-7 that one. I did found out this LDO pad pin-2 Vout is short circuit. I would like to explain more detail again what i had did...

Bellow is the circuit diagram.

+9Vdc Adapter -> +5V regulator (LM7805) -> Regulator +5V connected to Mbed pin-2, GND connected to Mbed pin-1 -> Connect Sparkfun Magjack PRT-08534 to Mbed ( follow this pin assign http://mbed.org/cookbook/Ethernet-RJ45 )

I make a small PCB board for LM7805 and Mbed connector on one PCB board. This to ensure no human error when giving supply to Mbed Vin or wouldn't happen voltage polarity problem.

1) After power is ON status (middle) LED is not turn ON. Then i measured the LD1117S33 regulator (which is beside the pin-4 to pin-7) Vout just 1.27V only and it slowly getting hot.

2) So, i tried to unsolder the regulator out from the board and measure the Ohm's regulator LDO PCB pad pin-1 (GND) and pin-2 (Vout). The measurement result is 1.2 Ohm, look like the LDO PCB pad pin-1 (GND) and pin-2 (Vout) is short circuit.

3) After remove the regulator I do check the regulator LD1117S33 Vout again. The Vout result is 3.3V, so the LD1117S33 component is in good condition.

4) When after removed the LD1117S33 and i tried to input the +5V to Mbed pin-2 again, I measure the LDO PCB pad pin-3 (Vin) i get +4.98V something. Which mean before or in between the Mbed Pin-2 (Vin) to LD1117S33 pin-3 (Vin) is working fine. Just LDO pin-2 (Vout) getting problem. I further measuring the Mbed Vout pin-40 and Vu pin-39 i get 3.3Vout and 0.6Vu.

5) Another testing i was did is i put the meter prod on the LDO pin-2 (Vout) and tried to use back the LD1117S33 +3.3Vout supply back with jumper touch the LDO pin-2 (Vout). The meter shown 1.27V again. Removed the jumper i get the LD1117S33 Vout +3.3V back.

6) I through it is something wrong with the PCB tack in between the LD1117S33 +3.3Vout and GND. I did check the on board 100nF cap they all connected to this LDO Vout. Which mean this Vout is system supply. Hopefully this short circuit it wouldn't get harm to Mbed. Another thing i did check all the Mbed 40 pin connectivity, there is not short circuit happen.

I wonder what happen to this Mbed after i connect the Magjack PRT-08534 it not working any more. Magjack PRT-08534 have using +3.3V which is supply from LDO and no GND for that. I don't think it can cause the short circuit.

May i know what can i do now? :(

Remove ethernet transciver i.c

Hello Lerche,

Thanks for your advice. I just brought not even use it till 2 days the thing already spoil, very sad. :( I would like to know what's the root cause, if the mistake done by me then next module i need to do it very carefully already. Otherwise i buy a new one, and do a same mistake then i can't afford to buy it any more T_T. This module is not cheap for me.

Hello Matheus Almeida ,

I'm not dare to remove the ethernet transceiver IC. To remove the IC not a big deal but to solder it...i don't know how to solder it back. Is there any other alternative rather than remove the ethernet IC?

I found that are a lot of people in this forum facing Mbed dead problem! Is it this Mbed had very frailty voltage regulation design? or lack of voltage/current protect?

My mbed died in an early stage as well. The power supply design is not full proof. I switched to Arduino, which is robust and forgiving.

By the way, it happened in the middle of a running program. Mbed started smoking and died.

Wen qian: seems likely that magjack caused problem. Check wiring for short circuit between 3.3V of magjack and gnd (shield of magjack) or short between 3.3V and TD+/- or RD+/-. Shorts could have damaged the ethernet device. Remove the ic. this leaves you with an mbed that might still work but without ethernet. Replacing the ic is probaly too difficult.

There are more reports on dead mbeds. However, some refer to software problems (not seen as USB device etc) and some are real hardware issues. Several of the hardware issues are probably the result of not reading the specs and doing things that are not very healthy for any device, like shorting Vout or forcing 5V on the Vu pin or feeding 8V to an inputpin...

Hello Wim Huishkamp,

Thanks for your advice.

I did check the magjack datasheet (http://www.sparkfun.com/datasheets/Prototyping/MagJack.pdf) before i connect it.

Ohm's measurement:

3.3V (pin-2) to TD+ (pin-1) = 0.9 Ohm

3.3V (pin-2) to TD- (pin-3) = 0.9 Ohm

TD+ (pin-1) to TD- (pin-3) = 1.5 Ohm

3.3V (pin-6) to RD+ (pin-7) = 0.9 Ohm

3.3V (pin-6) to RD- (pin-8) = 0.9 Ohm

RD+ (pin-7) to RD- (pin-8) = 1.5 Ohm

Look like in between TD/RD+ 3.3v TD/RD- is almost short circuit. This PRT-08534 type of magjack don't have gnd at the primary side (pin-1 to pin-8). Therefor, how ever i connect the wiring it wouldn't be short circuit in between 3.3V and GND.

Ya, to replacing the ic is very difficult for me. Before i removed it i would like to claim this module from NXP manufacture. Is it possible to do that?

The Ethernet ic is so sensitive?

Hi Wen,

Give us an email at support@mbed.org and we'll see if we can help get you up and running again.

Thanks,

Simon

Pins 2 and 3 are swapped in your message. If this is not just a typo, change the wiring so that 3.3V goes to pin 3, and TD- to pin 2.

Hello Simon,

I just send the email to support@mbed.org. Thank you very much.

Hello Hexley Ball,

Ya, you are rite. Thanks for your remind.

When i connect the wiring i'm follow case with Sparkfun PRT-08534 http://mbed.org/cookbook/Ethernet-RJ45.

I have another unit of MagJack but i'm not 100% sure what's the part number. I do check the connectivity then i found out it look like case with Han Run HR911105A http://mbed.org/cookbook/Ethernet-RJ45.

Does anyone can help me to validate the pin resistance on the Magjack PRT-08534 and HR911105A?

Now i'm worry. The resistances on the MagJack are all very low, any way of connecting it will short Vout to GND, I wonder if the short circuit presented by the MagJack has caused the LDO to overheat and fail?

Is there anyway to check or test the Magjack without connecting to Mbed? I'm worry my Magjack the one with the low resistances is broken and cause damage to the mBed.

Thank you,.

My mbed was controlling a MOSFET which is controlled by a 48V dc/dc current source converter. When I was taking the voltage reading of the various pins output from the mbed, the probe accidentally touched the Vin and GND of the mbed. A flash of light was seen and the mbed is no longer working. My guess is the mbed is fried.

Should I go ahead and remove the regulator and check the voltage reading?