I accidentaly powered my Arduino Uno with 24V through the 5V pin, like shown in this picture:
After that, I noticed that it was drawing more than 100mA even though I had nothing connected to it. I checked with my meter and there was a resistance of around 60 ohm between 5V and GND (even without the atmega inserted in the socket). When I power it, the capacitor C1 in the Arduino Uno schematics (http://brittonkerin.com/annotateduino/arduino-uno-schematic.png - C1 is in the upper left corner), which in the board is right next to the 3V3 regulator, gets very hot. When I try to upload a sketch, I get this error: avrdude: verification error, first mismatch at byte 0x0000 0xff != 0x0c avrdude: verification error; content mismatch.
If anyone knows what is causing this, please let me know. Thanks!
currentvoltage higher than 5 volts has the potential to damage a lot of components.
I would suggest you test the following parts:
The 5v regulator. Use a multimeter to determine whether or not the regulator is still able to supply a steady 5v.
Resistor packs. You can also test the resistor pack that is in the power circuit for the correct resistance.
The USB-Serial chip. If the regulator and resistors check out okay, a loopback test will normally indicate if the usb-serial chip is functional.
The atmega328 microcontroller. If all else checks out you can replace the microcontroller with a known good part.
You smoked the board. Unless you have surface mount repair skills, the board is toast. Get another.
After desoldering the capacitor, I noticed that it wasn't it that was heating, it was the op amp right next to it (a LM358). From what I understood from the schematic, it selects either external power or usb power, so if I desolder it, I might still be able to use it if I power it via the USB port.
The 5V regulator works fine, heats up a bit because it is supplying 100mA.
I have no way of testing the atmega328, as I don't have an ISP programmer or other board.
What's strange is that I should still be able to use the board, as the regulator is still providing 5V, however, I can't upload anything, so maybe the microntroller is fried as well.
2. Resistor packs. You can also test the resistor pack that is in the power circuit for the correct resistance.
What do you mean by resistor pack and power circuit? Sorry if I wasn't clear, the 60 ohm resistance I mentioned is an internal short in some component (I think), not an external resistor I connected.