Скачать или смотреть Bad Arduino Pro Micro's from GC_SUPERMARKET

Bought a bunch of Arduino Pro Micro's from Ebay seller GC_SUPERMARKET. which turned out to be not working properly.

After uploading the blink example sketch with the added line #define DEFAULT_LED 17 to make the Rx LED blink, the sketch doesn't run after powering the board up ana manual reset is needed to run the sketch.

When trying to upload a sketch to the board again, the board crashes when the arduino IDE resets the board by opening the COM port at 1200 baud. Upon crashing the Rx and Tx LED will flash alternately like in this video and the board is no longer reconized by the computer.

Since not just one but all the boards had the same problem. I had to find out what was going wrong. After a lot of testing and inspecting the boards I could find no hardware issues and the bootloader was fine too. But then when I checked the fuse settings I found out the manufactures burned the wrong fuse configuration.

It seamed the BOOTRST fuse wasn't programmed. so whenever the board was reset, the bootloader wasn't executed.
Using an ISP programmer I programmed the fuse (setting BOOTRST = 0) and the problem was solved. I could now upload sketches again.