When you plug it into USB does it have a normal LED power on sequence?
- About 5 seconds of dim blue
- One quick blue blink
- About 2 seconds of slow alternating blue and orange blinks
- About 7 seconds of fast alternating blue and orange blinks
- Slow alternating blue and orange blinks from then on
We mention these things because after that comes "bad sensor".
I wouldn't think that bad soldering would make one direction slow, but I could be wrong. I would still check the board with a high powered magnifier. I use a jeweler's loupe.