schematics for Technics

I am looking for information on a Technics tuner, ST-Z400 which I recently acquired along with the other parts of a "pseudo-professional" rack system.

In particular, I would like to know the function of the rear-panel input labeled "CONTROL". This is an RCA type connector, I think the function appears on many of the low-profile tuners Technics appears to have built on this same chassis.

Also, can anyone give me a source for schematics for this tuner, and/or the other elements of the system: SU-Z800 integrated amplifier, and SH-Z200 graphic equalizer?

Thanks in advance.

i have a technics su-z800 integrated amp with the same tuner

are you wanting to buy teh su-z800 integrated amp?
mine is in perfect condition
very clean inside and out.
im looking to trade it for a marantz set consisting of:
marantz 300dc amp ,3250b pre- amp, and 2100 tuner.
i will sell the technics amp interested?