I just finished building 16 of these with an after school group of 12 year olds. They all did a great job with their first soldering project, but we had trouble with one kit and I hope someone can help me troubleshoot.
The problematic kit works properly except that the LED in the lower right corner lights less brightly than the rest. I checked the solder joints and they are all nice, full and bright. I guess the only thing to do is to swap out that LED for another one.