I recently replaced the factory TunerList radio in my Renault Megane 2 (2003) with a Sony DSX-A400BT. Everything works correctly except that the radio forgets the settings, but it is not a problem of bad connections because the continuous power supply and the power supply from the ignition are connected well (I checked with a meter). I also checked all the fuses.
If I turn off the engine, close the door and come back (e.g. several minutes) the radio remembers the settings.
But while at a longer stop when I come back to the car, open the door, insert the card and press the start button, it turns out that the radio no longer has its settings.
This radio right after resetting has set 1:00 a.m. and demo mode, e.g. I observed 1:40 a.m. which suggests that the radio reset 40 minutes ago and generally every time it is 1:XX, this morning it was e.g. 1:53 a.m. So it looks like the radio reset many times during a longer stop.
I've connected properly exactly with manual (http://sony.co.uk/electronics/support/res/manuals/4573/45734042M.pdf) and tested red / yellow cables in my car. The car's yellow cable which have power after then the engine is off is connected with the radio's yellow cable which is described as "continuous power supply" in manual.
I would like to add that the same radio was previously used in Fiat Brava 1.6 1997 and the radio always remembered the settings.
Tip: I asked the same question on another stack exchange: https://electronics.stackexchange.com/questions/451915/unfactory-radio-forgets-its-settings-at-a-long-standstill