Direct your inquiry to JBird604. He used to play an ADC-4000 at church, and will probably have advice of how to narrow down your problem with your existing equipment.
In a direct answer to your question, though, occasionally Allen organs are parted out on eBay or other websites, but I don't recall an ADC-4000 being parted out yet. I also get from your post that you're not terribly interested in waiting for one to become available, either. Keep in mind that some boards are interchangeable between organs, while others are not. JBird604 can help you with that.
Best of luck finding out what is wrong.