This is a "Gemini Scratch Master PMX - 10 Stero Preamp Mixer w/ Box" That really says as much as i know about it. Kept in storage for many years. May have been bought at best buy according to a receipt that fell out from the 90's. Original box. More info can be seen in condition below:

Condition: This unit has been tested as far as i know to test it. Powers on and lights up. Signals pass through to amp and levels read on display. I can't be certain that every feature works as i have no clue how to test it or what to expect but i have no reason to think anything's wrong. This is being sold AS IS and may require some level of cleaning or work to get it properly functioning (I just don't know)

The only issue i know is this needs a new power cable. Uses a pretty standard 12 volt one that i had an adapter that fits. Adapter can be seen on back.

See pics for cosmetic condition. Condition reflects pricing.