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 ( 59K) 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 ( 51K)
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