Av reciever switching surround modes

[Peter Mead]

Hi,

I have a Hitachi HTA-DD3W av receiver that when I am watching a dvd or tv on Foxtel the receiver will chnge from dolby digital to pro logoc and lose sound, If I turn the receiver off and back on again it can come back to dolby digital again.
I checked all the wiring and cables and all seem ok so I am putting down to the receiver being old and on its way out
Please help with any thoughts anyone might have.