Established Member
On my Model 2 SCD there's a mixer plug-in. My guess this is for A/V cables going from the VCR to that? Is this Mixer thing on Model 1?
This is for use with a Genesis/MegaDrive 1.

You plug a cable in the MD1/Gen1 phone out & in the MCD2/SCD2 mixing in.Without this you won't hear sound effects when you use the line out plugs.