R4 Bi-Directional Quad Switch
The analog switches are as per the example given in the 1978 Motorola data book for the MC14007UB, and most likely also in earlier ones as well.
The functionality of this module was gained by adding a two bit binary counter to select between the switches, which were wired as shown in the schematic. The extra components, shown in blue, were mounted on a piece of matrix board with a stick-on prototyping IC pad set on the rear.
Note that the bidirectional switch is truly bidirectional since 1-4 can be used either inputs or as outputs. If jacks 1 to 4 are used as inputs, the unmarked jacks must be used as an output, and vice versa. Each pair of jacks is linked via a wire on the rear of the panel.
Photos are from a Serge supplied unit made in 1975. This is probably the first instance of a "curved line" graphic!
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