they use old CMOS 4016 quad bilateral switch ICs on
place of 'real'
switches. If you encounter one that seems to 'light up' but is otherwise
autistic, it almost always can be traced to one or more of the 4016s
dying. They are now made of Unobtanium, and the 'replacement' pinouts and
impedances are different, so a kludge is called for, if original 4016s
can't be scrounged.
What do you mean? CD4016s are still available from a lot of sources, even
Digi-Key. Is it an odd, non-DIP package?