Velodyne ULD servo amp serca 1991

I have a ULD 15 II B with 400 watt velodyne servo amp. I believe my servo amp is damaged. No sound is produced when I connect it to my pre-amp. However, the sub produces sound when connected to a reciever.

Any repair suggestions? Does Velodyne service the servo amp still?
You need the sub connected by both the coax and the speaker cables. I don't understand this part of the servo sub but that's how mine works. Mine is the same as yours if I use a different amp? Weird but.....
Call Velodyne service, they still service the amp.