Arduino Outputting Random Serial and rapid Blinking.

I purchased a few Arduino Nanos recently and when I connect one of them to my PC the L led blinks three times and then rapidly starts blinking. I have found multiple threads on this but I also noticed that the arduino is outputting various numbers over the serial console. Starting around 340 decreasing to 14, then restarting at 500, all the while in between it jumps around a lot but gradually decreasing. Sketches do not upload, but the com port is still visible to my PC and the software. The other one works and I am thinking this one may be faulty. Any suggestions?

Ship the faulty one back?

Or try to load the bootloader via ICSP and see if that solves the problem.

With just playing around with settings, I discovered the processor options under tools, and I had to set the IDE to use the old bootloader. Everything works now.


If you receive two and one works and one doesn't (seem to), it's strange that one has the new bootloader and one has the old bootloader. You might have received a mix of old and new stock.

The bootloader for original Nanos changed in the beginning of the 2018 and all originals shipped from Arduino after that should have the new bootloader.

Did you buy clones? If so, I'm surprised that one has the new bootloader.