Did it gradually or suddenly go wrong?

I'm sorry I can't answer that. I haven't used it for a couple of
years...

If you feed in a known accurate ,say, 1V pk-pk 1KHz signal in, does it give
the correct screen indication of 1V, 1KHz with relevant settings ?

I made another 2 photos. Used a HZ 154 probe on the internal CAL.-
outlet. Looks weird to me...

http://www.preamp.org/dinge/hm02.jpg
http://www.preamp.org/dinge/hm03.jpg