why no sound from subwoofer?

This is for a Carver AL-III speaker. The ribbon works fine, but the woofer has 0 sound. The cone looks good visually, the capacitors all check out as holding a charge, not short-circuiting, etc, and I replaced the fuse. Could there still be something wrong with the cap(s)?
What impedance does the woofer read?
I didn't have the bus plates screwed down tight, and yes the woofer impedance was low. Problem solved :-)