Hi Les, as a first step, I would disconnect the speaker cables in the Technics su-x501 and test if the same thing happens, if so, there could be a problem with the power supply or also with the speaker output
If it does not turn off, then I would start checking the speaker cables, along the way, in case there is any peeling, which could cause overheating
Once the cables were checked, I would connect the speakers one by one and test with each new reconnection until the source of the fault was detected
I hope you can solve the problem
Regards Franco Dosil

Hola Les, como primera medida, desconectaria los cables de los bafles en el Technics su-x501 y probaria si pasa lo mismo, si es asi, podria haber problema en la fuente de alimentacion o tambien en la salida de parlantes
Si no se apaga, entonces comenzaria a revisar los cable de los bafles, en su recorrido, por si hay alguna peladura, que podria generar un recalentamiento
Una vez revisado los cables, iria conectando de a uno los parlantes e iria probando con cada nueva reconexion hasta detectar el origen de la falla
Espero que puedas resolver el problema
Saludos Franco Dosil https://elektrotanya.com/technics_su-x501_sm.pdf/download.html https://elektrotanya.com/technics_su-x501_sch.pdf/download.html