Arduino Uno R3 no longer responds to USB (possibly fried)

Using Arduino IDE 1.x
1

So I've been using an Uno for some time now, and suddenly for no apparent reason (no power surges or anything like it as far as I am aware of) it is no longer talking to the USB.

I don't know very much about electronics or about how the Arduino works electronic-components-wise, but here are a couple of tests I did:

  • As far as I can see, the last sketch I uploaded is still running (sadly I was checking some new components, so the sketch is too simple to do real tests).
  • The MF-MSMF050-2 500mA fuse right below the USB port is not burned.
  • The 3.3V supplies 3.3V correctly, but 5V supplies less (~4V).
  • When supplying voltage directly to Vin, 5V is indeed supplying 5V.
  • All of the parts seem to heat up unreasonably, especially the 16Mhz...resonator? (not sure what the correct name is)
  • When directly connecting the pins of a USB cable to Vin, GND, TX and RX, the computer knows something was connected, but can't talk to it.
    When it is connected to the USB port, the computer doesn't even know anything was connected.
  • While RX is generally stable, TX keeps changing.
    I imagine this means that the computer doesn't do anything because it fails to talk with the Arduino, while the Arduino keeps trying to talk but it fails to reach the computer (but I am no electronics expert or anything close, so I might be completely wrong).

From the tests above my intuition tells me that there are two possible problems (one not disproving the other):

  • There is some issue with the voltage regulator(s).
  • There is some issue with the ATMEGA16U2 chip responsible for USB communication.

Is my Arduino fried?
And is there a chance for something like this to just randomly happen for no apparent reason?

Thanks for any help. :slight_smile:

/Edit

After some more thinking, here's a probable cause.
What I was testing was a 7-Segment 3 digit display. the circuitry is a really simple matrix of diodes...and I didn't use a resistor. I remember hearing that a diode is a component that will just allow any current to go through (unlike other components that will pull what they actually need), so is it possible that I moved really large currents from 5V to GND?
Here's the datasheet of the display http://www.py2bbs.qsl.br/projetos/freq_dl4yhf/TOYO-E30281.pdf
Basically 5V was connected to the digit pins, and I alternated GND between the segment pins (after a lot of testing to even find what pins were the digit pins).
I did really fast tests just to map the display pins to the segments (because that datasheet doesn't specify the order...), and didn't notice anything going wrong, but there you have it.
Can this be the cause?

2

spectralcanine:
All of the parts seem to heat up unreasonably, especially the 16Mhz...resonator? (not sure what the correct name is)

When the board is powered via USB? With only a USB cable connected to the board?

When directly connecting the pins of a USB cable to Vin, GND, TX and RX, the computer knows something was connected, but can't talk to it.

In every way, shape, and form that is a bad idea. Don't do that again.

3

Yes, only the USB cable is connected.

Why is connecting the USB wires directly bad? isn't it pretty much the same thing as connecting to the USB port?

4

spectralcanine:
Why is connecting the USB wires directly bad?

The USB data lines are 3.3 volts. You are connecting those to pins operating at 5 volts. You are basically creating a short-circuit that will damage one or both sides.

isn't it pretty much the same thing as connecting to the USB port?

Not even close.

Yes, only the USB cable is connected.

In that case, this...

All of the parts seem to heat up unreasonably, especially the 16Mhz...resonator? (not sure what the correct name is)

...is a strong indication the board is toast. It may be possible to resurrect the board by replacing the ATmega328P and reprogramming the ATmega16U2 but, given the list of symptoms, I doubt it is worth the time.