Sounds like it... Try shorting (a pair of metallic tweezer work fine) across the emitter and collector (top and right pins if viewed as mounted, from the front, IIRC), ie +5V feed and the common track for the LEDs.
LEDs should light up to max, indepedent of dimming level set.

This is by memory and for the 3-button version of the knob board.

/Michael