Brightness of Classics' display

[teenix]

(09-15-2020 11:35 AM)BusyCalc Wrote:  Hello,

I own several classic HPs and I noticed, my HP-35 (V3 - 1302S) shows the display quite dimmer than the other ones (compared to a HP-45 or a HP-80).

Is there any difference between models regarding this?

As far as I know, there were no improvements/changes till the Woodstock generation.

Thanks!

Kind regards,

Oscar

I assume all of the LEDs are uniformly dimmer. If so it might be that they were from a batch that ages a bit differently to others.

The power for the LEDs is supplied from battery voltage via the inductors and transistor switches in the cathode driver. The only common point here for all LEDs is the battery and the ground at the cathode driver, and the circuit paths for either or both may have increased in resistance over the years.

Maybe unlikely, but if the RC circuit has changed over the years and increased the clock timing for the calculator, the inductor charge/discharge cycles might be limited and dumping less charge into the LEDs..

Anything else that I can think of would cause different LEDs to vary in brightness, either in the same segments or single digits.

cheers

Tony