I was tooling along making progress just fine when I began getting erratic behavior from the connected SPI connected peripherals. All of a sudden my laptop unexpectedly shut down in an instant and I could smell the distinct smell of something cooking.
No more blue blinky lights and could not read or write the mbed. I quickly disconnected the 12VDC supply and USB cable. Found the chip adjacent to pins 1 & 2 too hot to touch and with obvious signs of overheating (next to 'VIN' marking).
I am not sure why this happened as the quick reference card clearly states that the board can handle up to 14.0V input and I am running from a 12V gel cell and polarity was correct.
Luckily I have another just in case this was ever to happen.
Does anyone know, is this the IC5 LD1117S33 shown on page 4 o 5 in the schematic design documents or is it something else?
It's not supposed to fry until after 15V input.
The max input voltage is 9V. Some early schematics and specs mentioned 14V, later versions state 9V max. See http://mbed.org/handbook/mbed-NXP-LPC1768
BTW: are you sure that the input voltage is 12V. Many cheap wallwart powersupplies are not well regulated and output voltage is much higher when the load is relatively low.
The fried device is IC3, a current limiting circuit for the USB powersupply to mbed. Note that you can still read the remainders of the code (FPF2)123 on the device in your picture.
The larger devices marked LD33 are the IC4, IC5 3V3 regulators.
I am not sure why the (FPF2)123 device broke down, maybe you accidentally applied 12V to the VU pin 40, which destroyed IC3 and shut down the PC. The PC shutdown was caused by the USB power being shortcircuited.
Another reason may be that the protective diode D1 broke down due to Vin being too high. That then destroyed (FPF2)123. The most likely reason is that IC4 and/or IC5 broke down as a result of the 12V inputs and the resulting shortcircuit also overloaded (FPF2)123.
mbed is probably dead, but you could try removing (FPF2)123 and D1. Dont connect the PC USB. Apply a current limited 5V to Vin and measure the two 3V3s. In case these are not present, replace D2 and then the LD33s and try again. Note that should this work then you still need to replace (FPF2)123 and D1.
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