Dual D.C. Sense Amplifier 4551C system building block
The module consists of a board with various active and passive components surrounded by an aluminum frame and a 22 pin male connector. On the solder side there is a lettered grid running down the side, which reads A-Z. There are two inspection stamps on the component side.
Digital Equipment Corporation (DEC)
Printed on the solder side of the module at the insertion end