Problem with Intermittent surround sound

I have a 20 year old JVC receiver with surround sound capability. I connected it to my smart TV with a digital optical cable. The surround worked perfectly and I was happy until the next day when I turned the system back on and the surround sound did not work. After changing several settings several times it did work again. but now when I turn it on the surround sound does not work. Any suggestions would be appreciated.