My TCL 55C2US TV has only one output port, optical audio, and a Toslink cable connects to the optical-in port on my Sony DA1200ES receiver.

I listen to TV via headphones from the receiver, however, the cans suddenly stopped picking up audio, so I'm trying to trace the fault.

The receiver end of the Toslink cable, when detached, shows a steady red light. Is this normal? If so, I guess the TV output is working properly, which could also mean that the cable is OK. Which perhaps means that the receiver's optical-in circuitry is faulty?

Comments would be appreciated