Arduino strange behaviour

Development Tools IDE 1.x
1

I have an Arduino Nano Atmega 328p. Just recently, when I was going to connect the 5V pin to the D2 to create a "1" signal, I've overlooked the GND pin which was adjacent to D2, I noticed a smoke and the power LED went out. I immediately disconnected the Arduino from my computer. I was afraid that I have fried the circuit that I was eager to know whether it still works. I checked if there was burnt parts by touching the ICs with my finger to see if it's hot. Then, my assumptions were wrong. The ICs were as cool as they were before I use them. So I plugged it in back to my computer, I notice the power LED is on but the LED light is blinking erratically. I twisted and jolted the USB cable to see if it's the port's fault, at some point my computer sounded a connection tone. As if the computer still recognizes it. And it does, at the Device Manager I see the Arduino under the LPT and COM ports. But the LED is still blinking erratically and after a couple of seconds the power light went out. I disconnected it again left it for a couple of hours to see if leaving it for a while will do the trick. After waiting for about 3 hours, the Arduino still behave as it was. I was going to conclude that my Arduino is fried, because the Power LED isn't on anymore. So I made a quick surf on Google related to my problem, I found a similar accident where he has connected the 5V to the GND by mistake. It was stated that the Arduino did a protection circuit break in the polyfuse to cut the power just in time to save the microcontroller. To return the Arduino to its normal state, I'll have to leave it for at least 2 hours to let the polyfuse resettle. But I plugged the Arduino back just 10 seconds after the accident. At this time, my Arduino can still be recognized by my computer. I was relieved that the Arduino started to work normal again, as a matter of fact the program I upload inside is still functioning. However I have this issues:

  • It disconnects and reconnects at some time
  • The Power LED goes out which would require me to disconnect and reconnect the board.
  • The LED light blinks wildly on an unpredictable manner until the Power LED goes out.
    What is wrong with my Arduino? Is the voltage regulator damaged? As the other components are still working.
2

Two options to try would be to run the board on a external 5V supply on the 5v pin, Or you can meter the voltage on the 5 and 3.3 before the board get flaky and again after it does to isolate the issue a bit more.

3

The arduino is working properly now only if I power it from the Vin. The readings in 3V3 pin is 3.90 V and in 5V it's 4.81 V. I am connecting the arduino now by cutting off the power wires from the USB and left the data wires intact. The cutted power wires are then connected to the Vin directly.