HP 35 display

[teenix]

The faint display might be due to the cathode driver for that digit not fully turning off causing a ghosting effect and is due to the multiplexed nature of driving the LEDs. You might notice that it changes when you key in numbers.

There are many instances of failing LEDs either fully or partially and can be simply put down to the age of the calculator. Nothing manufactured lasts forever so sadly that will be the fate of all these LED displays and/or the circuitry that drives them - but not for some time to come of course :-)

Chaining the calculator to a desk is probably desirable as they were new, expensive and probably tempting for someone to 'borrow'.

cheers

Tony