[parkher]

The on/off button was not working, because its micro switch broke off. Both glue and soldering (rather its pins). Or perhaps it was not properly glued in in the first place and hanging in the air.
Because from the very beginning the button was protruding a few mm compared to the other unit, I even liked it, it was easier for my fingers to find it. I am guessing, therefore the amplitude of the push on it was not limited by the edge of the board (as probably normally is), the whole force/amplitude of the push had to be taken by this tiny micro switch.
Anyway, I can fix it, but it would be easier if I could get an identical new switch rather than to use the same one with no pins left to speak of. An additional complication is that it has to be glued and soldered to the inside of the board, so the board (possibly, with the screen) has to be removed. Well, perhaps it might be enough to lift the corner, but because the whole screen seems to be lifting as well, there is a danger of breaking its glass if it remains fixed at some other points. Anyway, I already unfastened and lifted that corner without damaging the screen, enough to get a good look and possibly enough to fix it. For now, I left the outer button removed so I can easily perform on/off with an appropriate metal object. And I can simply solder there two wires for a temporary switch.