I just recently had a RXV21 board that I inserted into the backplane and then completely hung a few bits on the bus. It was a DC005 bus transceiver chip that had failed.
First it seemed impossible to find such a chip, but then I recognized that Signetics had put their own code own them as well, C2324N. Searching on Ebay gave this result: http://www.ebay.com/itm/281679682476 I bought some and they just arrived and worked perfectly. /Mattis
