The onsemi CNY171TM is a single-channel optoisolator in a 6-DIP (0.400", 10.16mm) through-hole package, with a DC input LED and a phototransistor output that brings out the base pin. The current transfer ratio (CTR) is specified at 40% minimum and 80% maximum when the forward current is 10mA, which defines the gain margin for the driven load. The output transistor can handle up to 70V collector-emitter and 50mA continuous current, with a typical Vce(sat) of 400mV at the rated drive — enough to directly sink a logic input or a small relay coil.
A pin-to-pin functional equivalent from the same family (CNY17 series) may exist, but no cross-reference is officially documented — verify the CTR bin and base-pin connectivity against the original design before substituting.
The 6-DIP package with 0.400" (10.16mm) body width and 2.54mm pin pitch is a standard through-hole footprint shared across many optoisolators — the board layout is straightforward and the tube delivery suits hand-insertion or wave-solder assembly.