I didn't use it as a scope for quite a time now, say, two months.
I tried the signal generator lately, but it had no output.
Last thing I remember was checking the new software 188.8.131.52 and
playing with math functions.
I checked the scope again this morning. Attached please find the
waveform. It was a clean 1kHz square wave with 200mVpp on
channel A only. Channel B followed without any probe attached.