Backwards LEDs Don't Work

Good lesson today as I tested out the battery status LEDs on the side of our main controller board; the polarising mark on the WS2812B smart-LED isn't on pin 1, in fact it's opposite pin 1.

I'd populated the board and had assumed the chamfered edge on the LEDs was the pin 1 marker. There was a 1 next to one of the pins in the silk-screen so I placed the part and went on to start testing with Python. Nothing was happening when I ran the various test scripts for the rpi_ws281x library. I decided to double-check the LED pinout, and sure enough pin 1 wasn't where I thought.

Pinout of the WS2812B LED, the marker is near pin 3.
Note the chamfered edge is on pin 3!

The parts are too thermally sensitive (the plastic case started melting before the solder melted) to remove with hot-air. I ended up cutting them off the board, cleaning the pads with a soldering iron then placing new parts. Fortunately I had a reel of 1000 of them! Once they were round the right way we got pretty rainbows from the test script.

Rainbow pattern on 5 neopixels.
Finally, some blinking lights!