I've had the same issue when assembling mine, and I bought 8 of them!
I just kept doing trial and error. Typical things - holding up to lights to see any bad connections, applying pressure when lit to see if there's a flash, etc. I also soldered while lit to see what happened. Dangerous...
My first year with 16 channels of LOR goodness
http://www.youtube.com/watch?v=uwz2nq9hNfA#ws
http://www.youtube.com/watch?v=qtI7998dvXU#ws
http://www.youtube.com/watch?v=Kzk4hNKg4tk#ws