I had a malfunction of some sort that left my Arduino Uno unusable -- I can no longer upload to it. Using the loop test I found here, I have determined that serial communication has truly failed -- Serial Monitor works fine with my "good" board but does nothing with this other board. Am I correct in assuming there is nothing I can do to repair it? Is there an alternative route for uploading to the board? Thanks.
yes, ISP interface
Look at "Arduino_as_ISP" tutorial
Not so sure. What kind of Arduino we're talking about (Uno, Mega, Nano...)? Are both the "good" and "broken" ones the same modem/manufaturer? And it is an original Arduino or a clone? Are you absolutely sure you have the proper serial USB driver installed? And haven't anything attached to pins 0 and 1?
Apart from uploading, if the previously loaded program writes something over the serial, if you attach any serial monitor (like the IDE one, or any other like putty, MobaXterm, etc.) and testing some speeds (starting from 9600 up to 115200) can't you see either anyhing, or garbage, or what?
Thank you! This is very helpful. I will see if I can get a diagnostic sketch uploaded and determine which pins (if any) still work.
It's an UNO. As far as I know, the boards are identical (I ordered them all at the same time) and original. The loop-back test works on the good board, and fails on the bad one, so I don't think it's anything to do with the USB cable or driver. I am going to try bypassing the built-in uploader and see if I can get a sketch loaded that will let me check the status of the pins.
You should be absolutely sure about that, because the loopback test (quote from here) will always fail for the CH340 USB to serial chip used on some derivate boards.
Anyway, if you can try ISP and solve, ok, but I still suspect it's not a UART problem: excluding you made something dangerous for that chip I've never had such kind of damage even with "chinese clones".
Have a near look at both boards and compare all the chips, especially the one next to the USB connector (if needed, link the exact board you bought, and/or upload here a clear and detailed photo of both).
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