I think I have your answer if you have not figured it out already.
There are 2 tiny set screws in the record knobs. If you push the top (left ch.) slider left to the record position you will see the screw in the right ch. knob below. If you then do the opposite you will see the screw in the bottom of the left channel slider.
They are face to face. Bottom of left ch. knob, top of right ch. knob. so if you move both you would never see the set screws.
I know this because I collect old consumer machines and have one with the same transport. These were also marketed under Craig and Channel Master as well as Sanyo. Hope that helps.
BTW, these have that cool "joystick" transport control shared with smaller Craig mono battery portables. I always liked those as opposed to mechanical push buttons or the ubiquitous lever that so many consumer Sonys and other brands have.
I think it is used on a Lafayette consumer stereo early Japanese deck I have and also on the rare Newcomb 10.5" semi-pro tube machine, which I wish I had. :-)