Below is a complete hardware-diagnostic checklist for the one HexBright that refuses to upload while your other two work perfectly on the same Mac, cable, and port (/dev/cu.usbserial-0001).

We’ll prove whether it’s bootloader dead, FTDI chip dead, ATmega328P dead, or just fuses/reset.

1. QUICK CONFIRMATION: The Good Ones vs. The Bad One

Test Good HexBright Bad HexBright
Plug in → green status LED blinks every ~2 s? Yes ?
Press reset button → LED blinks once? Yes ?
Serial Monitor (?) → replies HexBright Flex …? Yes ?

If any of the above is “No” → hardware problem.

Let’s test step-by-step.

2. TEST 1: Green Status LED Behavior

  1. Unplug the bad HexBright.
  2. Plug it in → watch the green LED (near USB port).
Observation Meaning
Blinks every ~2 s Bootloader alive → FTDI + MCU talking
Steady on / off Bootloader not running
No light at all Power issue or FTDI dead

If no blink → go to TEST 3.

If blinks → go to TEST 2.

3. TEST 2: Serial Monitor Query (Bootloader Test)

  1. Tools → Board → HexBright
  2. Tools → Port → /dev/cu.usbserial-0001
  3. Serial Monitor → 115200 baud, No line ending
  4. Type ? → press Enter