I don't know about the SA-7, but the SA-5 doesn't have an on/off switch as such. Pressing the shutter button halfway activates the autofocus and turns on the light meter. The camera switches off after six seconds of inactivity to conserve batteries, though the shutter can still be released accidentally. Turning the mode dial to the "L" position will lock the shutter and prevent accidental release.
You can find a manual for the SA-5 at http://www.butkus.org/chinon/sigma.htm . It's not ideal, but it should help you get started.
Answers & Comments
I don't know about the SA-7, but the SA-5 doesn't have an on/off switch as such. Pressing the shutter button halfway activates the autofocus and turns on the light meter. The camera switches off after six seconds of inactivity to conserve batteries, though the shutter can still be released accidentally. Turning the mode dial to the "L" position will lock the shutter and prevent accidental release.
You can find a manual for the SA-5 at http://www.butkus.org/chinon/sigma.htm . It's not ideal, but it should help you get started.