The AR3a was a good speaker in it's day but it is long ago obsolete. I don't think I would repair a non-working pair. They do look great and have solid cabinets but the drivers are fairly low quality compared to today's designs. I'm not sure it's even worth reworking their best speaker the AR-LST, times have moved on.
If you can do the work yourself, it would be an interesting project. Remember these speakers take a lot of power, you'll need a powerful amp.