Coromonadalix,
As I did not want to give up, I tested a 3rd keyboard of my stocks.
After removing the ps2 wire, I soldered mine with my din plug.
And then, surprise, it works, I could go in the bios. Murphy law!!
More surprisingly, the 54810A oscilloscope detects the IBM hard drive ( i think it's was out, to much noise!) and loads me a .... Windows95.
A time machine. LOL.
For now, I will check the config, because the floppy drive or lz120 is not recognized.
Ditto, I have nothing on the screen of the oscilloscope (no backlight) to be seen later.
I will solder a cable to have the several +5v and 12v for, subsequently, connect Cdrom drive, Sata disk (with adaptator ide sata), etc.
I put aside the IBM disk before backup.
NB: I will put the cards back on the same slots, because Win95 asks me to modify. The less I touch, the better is.
cdt