Searched for an answer to this but didn't find one elsewhere:
I've got an Arduino Diecimila that's been running fine for months. Yesterday, a ULN2004AN array that I had connected to seven of the digital outs burned out. Subsequently, when I connect power to the Arduino, the power LED lights up briefly and then fades. So for practical purposes, the board is dead at this point.
Can anyone shed light on which component might be blown out? The voltage regulator, or? Trying to see if I can switch out a part to salvage it.
To test the FTDI chip and the voltage regulator, I'd pull the atmega. You can use a little screwdriver for gently lifting the chip until it comes free. This has to be done symmetrically from both ends of the socket, with a lot of care as to not bend or shear off the pins.
Then if you power it up see what happens. If the power led stays lid, check the supply voltage that is available on the headers. For testing the FTDI, just wire the RX line to the TX line and use the IDE's serial terminal. If you get echoes for typed stuff, it is still alive.
For testing the voltage regulator (only applies to external power), you need to switch the jumper to external power and supply at least about 7V to the jack. See what happens. No USB connection necessary.
New atmega chips with a bootloader are available from the usual suspects for little money.