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Author Topic: [SOLVED] Sketch upload failed after (maybe) shorting pins to 12VDC  (Read 351 times)
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Hello People,

I recently got in to Arduino and thought I'd share one of the problems and solutions I've come across.

I was using my Uno to drive a small motor (+12V supply with L293D) and take in a couple of button inputs when I must have shorted some pins (maybe +12V) to Digital 1 pin (Tx) because I could no longer upload sketches. I tried swapping the 328p but that did not fix it. I tried rewriting the firmware to the 16U2 but that also did nothing. Then I started to investigate with a scope and found that the Tx signal coming from the 328p looked good on the its side of RN4A ( full +5 to 0V swing) but not on the 16U2 side (+5 to +4.6V swing). I'm assuming I somehow half fried the input on the 16U2 causing it to pull the line high all the time. I figured the only way to fix this was to replace the 16U2 but I don't have the tools to do that so I thought up a different fix. I needed to eliminate the voltage drop across RN4A so I soldered a short across it. I know that this resistor is put there for some sort of protection or buffering but I don't care. I'll take the risk to get my board back up and running. With the resistor shorted I can again upload sketches to my Uno. Because of this mod i'm going to try and avoid using pin 3 (tx or Digital 1) of the 328p in my projects with this board.

I hope this helps someone at some point. I know I couldn't find much to help me after I tried the chip swap and firmware rewrite.

If there's a better solution to this problem please let me know. I don't mind the jumper but it'd be nice to fix it properly.

-Dennis
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