harmon/kardon AVR120 switches to the standby mode after 90 seconds

Hi, I have a harmon / cardboard AVR 120 receiver and it play normally for about 90 seconds and switches to the standby mode. To play it again the standby switched needs to be pressed and it will play normally again for about 90 seconds, and switches back to standby.
Is there anything I can do to rectify this, or maybe bypass the standby mode?
Thank you so much for your help.
NW