This has happened to me(several times) on a 1428 digital many years ago---but I can't seem to remember how I got it to be normal. The only thing I can think of is wiring/re-seating of an amphenol--or something in that area. Do you have a 66 block to modular adapter that goes right on the block?? I'll try to find some old customer service notes...maybe something will spark a part in my brain.