Velodyne FSR-18 Fuse Blown

Got a Velodyne FSR-18 sub last weekend with no power. After opening up the plate, I found the fuse is blown. After I installed a new fuse and turned it on, it blew again. Then I connect it to a dimbulb tester, the bulb lights on, so there is a short somewhere. I can't find any burn mark or bad capacitor visually. Test few big resistors and they seem to be fine. The woofer unit itself measures 3.4ohms, and tested with a battery and can hear some sound.

Anyone here with experience with repairing these subs? What are some of the usual failure spots?

Thanks!