I have a 4000 keyboard adaptor and noticed that the one pin is bent over so that two pins go in the same hole. I tried two normal 4000 keyboards and the machine appears to have the keys stuck. I can't verify that these keyboards work at the moment. However the keyboard connected with the adaptor with the bent pin into what appears the same hole as the adjacent pin works without fault. Can't say I had ever noticed before. Is that normal. Just that with age the adaptor is getting a little loose and I was kinda hoping of trying to get a normal 4000d keyboard working with it. I thought I had another adaptor but can't find it.
Hope that made sense.