Front of M993B Interface Card. This card connected the RK05 drive to the Omnibus controller RK8E using 2 ribbon cables. This version has an IC (DEC5384 similar to SP384), diode (1N748A), resistor, and transistor (DEC 6534B) that they didn't install on the M993C (376K) version of the card. This appears to drive the RK05 DC Low signal from a buffered copy of the Omnibus Power OK signal. The M993C directly connected these signals. It also changed a connection from AU2 to AU1 which may not have any signal on it. With my PDP-8 both versions of the card work. Back of board (309K)
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