@glupson, the service manual shows an arm return mechanism like that of the “lesser” semi-auto Technics turntables of the late 70’s and ‘80’s. The mechanism is driven by a small gear on the platter spindle and engaged either mechanically by the arm pivot contacting a lever when the end of play is reached, or by a solenoid that is triggered by the stop button on the plinth. The SL-Q2’s automatic mechanism probably shares several parts in common with the lower end belt drive units, so parts and donor units should be plentiful on fleabay.
If neither works reliably, I would first examine the spindle gear and the much larger main gear for missing teeth. If only the stop button is intermittent, try lubricating the solenoid plunger. I believe you can download an electronic copy of the service manual from the vinyl engine site. If you are unable to locate it, I can scan it to PDF and email it to you.
If neither works reliably, I would first examine the spindle gear and the much larger main gear for missing teeth. If only the stop button is intermittent, try lubricating the solenoid plunger. I believe you can download an electronic copy of the service manual from the vinyl engine site. If you are unable to locate it, I can scan it to PDF and email it to you.