Im having an issue running my Uno off of a battery. It worked fine about a week ago, then today when I connected it to a USB battery (one of those rechargeable packs), it didn't power on. I metered the power coming out of the battery and it was at -4.91Vdc (I cut the USB cable open and metered between the Red LEad (+) and the black lead (-) ). I thought it was odd for the power to be a negative number, so I connected it to my PC.
When I connected it to my PC, the 8 component next to the USB connector (see photo) got screaming hot and it still didn't power on.
I think that particular component is a fuse, but I'm not sure how to reset it. Can I fix this or did I fry my Uno and need another one? And did the battery pack kill my Uno?
The fuse is probably ok. It is regulator IC for 5V what was probably hot - between fuse and power connector. However, both ATmegas could be damaged also if there was negative voltage.
Handy person would be able to repair it with appropriate tools but it is lot of effort though. Fortunately, the board is not expensive.
It is good idea to power up the board via the power connector. There is protective diode in the path but the voltage have to be slightly higher, something around 6.7V is ideal.
That device is a polyfuse type of device, remove power and let it cool, it will reset. Can you post a schematic, the connections in the picture are confusing.
I'm not clear if you connected the power the wrong way, from your description that seems possible. If you have then you have probably done permanent damage. If it's not damaged then it should be OK connected to a computer USB port.
I figured out the problem, I had shorted the +/- by accident downstream of the Arduino (on an amplifier). That was causing it to clamp at that component. Fixed my soldering problem, did not kill my Arduino, circuit works!
