41CX LCD viewing angle

I have a 41CX halfnut from 1985 which has mediocre display contrast when viewing at 90 degrees but good contrast when viewing from below (such as when it is on a desk in front of you). I don't see this behavior on my 41C or CV fullnut. Is this normal for some 41's, or my LCD dying?




I have a HP-41CV fullnut, the contrast at 90° is very good (it has a great viewing angle).

The display uses different voltages generated by a regulator chip in the fullnut, in the halfnut I really don't know. If you open it try to check all contacts.

Best regards,



David --

On loan, I have a 1987 halfnut 41CX with the very same display problem. The unit is also somewhat sluggish in its response, and shows signs of having been dropped or banged against something.

My own 1986 halfnut 41CV exhibits neither problem, and is cosmetically and functionally perfect.

Low internal voltage due to damage or broken circuitry?


Halfnut models are capable of changing the contrast settings, but unfortunately HP never got to update the function set to include control on this, so you'll need a (EP)ROM with the function actually implemented.

Or if you can key in MCODE, this is the rutine that will do the work. Input the contrast value (from 0 to 15) in the X register, then execute the function.-

094 "T"
013 "S"
012 "R"
014 "T"
003 "C"
0F8 READ 3(X)
38D ?NC XQ
008 ->02E3
0A6 A<>C S&X
130 LDI S&X
010 CON: 16
306 ?A<C S&X
01F JC B8BC +03
085 ?NC GO
0A2 ->2821
0A6 A<>C S&X
168 WRIT 5(M)

Best, ÁM.


This is how all HP41 machines behave. Fullnuts were designed to look best straight on, halfnuts at an angle.


Thanks everyone! It's nice to know there's nothing wrong with this calc. It would still be nice to have a way to adjust contrast. What's the path of least resistance to being able to write and execute MCODE?

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