Unfortunately, these older systems lose value rapidly and the cost of repairing problems like this can end up being as much as buying another system! Actually, you might be surprised to learn that JVC Service still sells many accessories and components from older systems. You can buy this sub woofer for less than $100, which should easily beat any repair cost you'll face. It may even come with the satellite speakers. The part number is VSDT2000R-SPBOX
NOTE: JVC Service has a free shipping coupon going on right now, so you'd want to use that: DZYZXFX49GYZZ81
Also remember that there's a standard connection between the head unit and OEM sub woofer, so you're free to use a non-JVC unit. I would try to find one with a comparable power rating. Of course, the only drawback is that it won't blend in with the unit... but then, the sub woofer is usually tucked away out of sight.