Sanyo 6100 dvd player-disc tray automatically opens whenever power is on.

Have you checked to see if it is off track?
Sometimes when these machines get bumpbed, dropped, or fall they can jump track.
You have to take the cover off and inspect to see if it is off track when it closes and opens. It should go all the way back on the track when it closes. Be careful not to shock yourself. If it is on when you do it and your hand touches the metal parts inside you can get seriously burned or shocked.

you should try inspecting & servicing the tray transport mech first
and then the tray sense swt.