After a two hour online flight close to approach, I noticed I am unable to change any NAV frequency by mouse clicks on the radio panel. Although the +/- symbol appears, clicks have no effect in all frequency fields. Other click commands do work (overhead, FMC etc.). Maybe related: Programmed the flight plan incl. SID/STAR into FMC, I was having both LNAV and VNAV activated and got the message "check MCP alt" and then "unable to reach destination" (or similar) on descend as it was probably too steep. So I programmed a hold in order to orbit to a lower alt for approach, after programming that hold and setting MCP alt to the selected exit alt (VNAV disenganged when programming the hold), the freq. buttons ceased to function.Maybe related as well: I noticed during start-up that the cabin temperature gauge stayed on 0

Over the weekend I had the problem of nothing happening to the radio....Until I turned on the battery. Had me wondering what the engine driven generators and IDGs are for?

Maybe related to that. I checked if all the switches are in the right position, however I didn't try to switch off/on the battery (well, during flight) to see if it resolved the problem. When saving a plane on ground, some switch settings get reset the next time I load the plane. However, I am not sure if the setting as a whole is reset or just the graphics. For instance, I don't hear any humming sound, although battery is switched on. If I do switch it off/on again, the sound starts. Same with engines, as described in the earlier post - best is probably to go through the checklist item for item, regardless of the switch position... I'll try to reproduce this tonight.

"The overhead's backlight got on, but just for particular gauges, although it can't possible have any power as external nor APU BUS are connected."Had a look at the Wiring Schematics and you seem to be right, Nik. All the overhead instrument/panel lights appear to be powered by the 28Vac Transfer Bus 2 (Section 2). "Maybe related as well: I noticed during start-up that the cabin temperature gauge stayed on 0