HP 41CX Annunciators Become Visible with Long Inputs

[brouhaha]

(01-22-2023 06:28 PM)akpoff Wrote:  I have a 41C with a fullnut board in it. I could try swapping them to see whether the issue is unique to the board or the display. Does anyone know whether swapping between models will work?

Fullnut displays are mostly interchangeable, but they did go through multiple vendors and revisions, so there two known issues, one mechanical and one electrical.

The really old revision F display driver, with the hybrid covered by a plastic cap, needs C2 on the logic board to be a 0.01 uF capacitor. The revision G driver needs a 470 pF capacitor. Having the wrong capacitor is only a serious issue if using the revision G driver with the .01 uF capacitor, which reportedly causes display flickering. This is from the 41C/CV/CX service manual, service note 41C-13, dated 11/21/79.

The mechanical issue is that some versions of the LCD use different clips and locators than others. This is covered in the same service manual, in service note 41C-58/41CV-19, dated 7/23/82.