How can I restore the Audio output from my Philips FW375?

My Philips FW373 Surround sound Audio system works fine for about 20 minutes and then the audio output just stops, it doesn't matter if I'm using the Radio, the tape player, cd player, TV or Turntable input. switching off and back on again clears the problem for another 20 minutes or so.

The front panel display does not show any problems.

Thankyou in advance for any assistance you provide.