Using a kenwood audio video control krf-v5200d

I have owned my Kenwood VR 5090 since new for 5 years now. Recently when I start to play my dvd's on 2 different -players the reciever will not detect the dolby digital source. I will have to play with it for several minutes, Going from input souce to input source and switching between dvd1 dvd2 thx off and .Until it finally starts working. The dolby digital indicator will flicker as not detecting the incoming signal.I've checked all the wiring and audio cables. Never did this before Email is pamang7@aol.com.......thanks............Angel