Protection circuits...
...usually will activate if there are shorts in the speakers or cables, the unit is overdriven(thermals) or if the internals are out of tolerance...
If you have disconnected the speakers AND wiring and...
Allowed the unit to cool down and reset itself and...
It still isn't working, there is only one choice left...
Servicing...but quite honestly, you will probably be better off looking for something more a, er...current to replace it with...and don't get me wrong, I have a strong attachment to my old gear, but there comes a point when it's time to say goodbye...sob...as I recently did with my TEAC A-650...
jimHJJ(...unfortunate, but true...)