I have an HP-35 with a bad display: it only shows one digit on two of its segments, like this:
5 5etc. When I input a long number, the display becomes brighter and brighter, and the numbers blur into an '8'. My guess is that the cathode driver is broken, and keeps on enabling these two digits instead of cycling through the display. Is it likely that this is indeed the cause, or could it also be caused by a bad connection somewhere?
3 3
8 8