I found this calculator on a flea market long ago. Actually, I bought it to use the keyboard for some somupter experiment, but fortunately I never came to dismantling it. As I got more and more interested in old display technology, in early 2000 I decided to analyse the circuit to see what I could learn from it for my own nixie projects.
The supply voltage is -24 V for the IC and the display, and +140 V for the display. The display is driven by discrete driver stages (using discrete transistors, no IC's). There are 8 digit drivers and 8 segment drivers (including decimal point). The current limiting resistors are not in series with the anodes and anode drivers, as is often the case with multiplexed nixie tubes. Instead, current is limited by the segment (cathode) drivers.
When I turned on the calculator, the display remained dark. I measured the signals on the display. None. Looking for signals on all pins of the IC I found none either. The IC seemed to get power, though. The clock signal was missing, so I checked where it was supposed to come from. The clock oscillator, an astable multivibrator worked, but not very well. It turned out that the driver transistor that drives the IC was faulty. After replacing this transistor, I had a working calculator!