Pictures of your repair job might help, but could really only be guessing at this point. When you had it a part, and fixing the PCB, bet there were a few thin, weak wires tangled around in the way. Would check those over. On the PCB, where you soldered, did you clean up the flux, or just leave it? Sometimes tiny beads of solder can be found there, look through a magnifying glass. Check both sides of the PCB? Sometimes hard to notice when its a two sided board, only a couple of traces on the top side.
Other than those guesses, pretty weird stuff. Kind of a simple circuit, would think it fail completely. How much brighter should the lamp be?