If the power to the receiver (AVR300) is shut off even for very brief periods I loose all the settings! The unit should last up to 2 weeks without this problem, but the problem occurs as soon as it is switched off.
I checked with my manual and in order to completely reset the unit I have to release the main power switch and then press the AM/FM and Dobly PR switch whilst pressing the Power switch again. The problem is the unit goes back to the factory settings every time the power is cut. An option is not to turn the unit off but from time to time loss of power is going to happen.
I see. Different models. Mine has a lighted electronic switch which you do use, and a mechanical one you shouldn't (except when a friend did, and when the babysitter did; and then I have to reset everything!)
I rechecked the manual and there is no mention of not using the Main Power switch (the one you refer to as mechanical), it just says "in normal operation the swith it left in the ON position". Anyway the issue is even if the power is cut to the unit for any amouint of time (e.g. if a fuse blows) the unit loses its settings. According to the manual the unit should last about 2 weeks without this issue.
Same problem with my AVR-430. Any power out or main switch off, I loose everything. I e-mailed HK and they answered saying the unit is defective - should be returned to an authorized service center. I cheked a friend's AVR-7300 and the setup holds all data when main power is cut.