41 cx LCD question


I am looking at a 41cx that might have a problem and I need ya'lls' advice.

If I put in a command like XEQ CLOCK as I press the keys I get LCD "garbage" on the right side of the screen (sometimes).

BUT, if I press ALPHA and just randomly put in letters it happens much less often.

Any ideas what could be causing this. Is this a loose connection?




can you identify what type of 41 is yours? Say, is it a fullnut or a halfnut?

Externally you'll have differences in the LCD module and in the key-pressing feeling. Look at the picture below.

If it is a fullnut, chances are you have just a bad contact between the conductive polymer and the LCD, or even a faulty, cold soldering in the LCD assy.

Please, let us know.

Best regards and success.

Luiz C. Vieira - Brazil


Ah, I forgot to mention it is a full nut. From my understanding the fullnut has a more complicated electronics vs. the halfnut. Correct?

What are my options if it is a bad contact or solder. I can eaisly build a PC from scratch, BUT the idea of taking one of these apart is rather unnerving.



Hi, Joe;

actually, the fullnuts are the ones that allow repairement, against the simple yet hard-to-repair SMT-fashion halfnuts technology. The fullnut's LCD assy allows you to remove and, in some circumstances, successfully repair it.

In your case, I would first try to resolder the small metal contacts (bridges) connecting the LCD assy to the keyboard PCB. I built a PDF with some pictures that show a step-by-step procedure to open a fullnut and remove th LCD assy. Of course, you'll see how to get there and resolder the bridges, right?

I sent you an e-mail with the e-address you can download the LCD_remove.pdf.



Hi Luiz

Can I have the LCD_remove.pdf too?




I'd like to have a copy, too.
Thanks in advance.



You need to open up the machine and clean all the pressure contacts with alcohol. Also clean the back of the LCD and the LCD connections with alcohol (I use 90%+ isopropyl). Do not let it drip onto the LCD window as it will leave a white stain that would need to be polished out... if on the inside of the screen you would have to remove the LCD module. I have found a LOT of flakey display problems due to invisible contamination on the LCD or contacts. Also go down the row of LCD connections and gently pry upwards on them... bad connections will pop loose and need to be resoldered.

As a last resort the HP41 service manual on the HPMUSEUM CDROM set has instructions on disassembling and cleaning the LCD module itself... a definite last resort.


I guess you have had this problem yourself. I spoke to someone else who has a 41cv and a 41cx. He has the problem with both of them.
Contacts,huh? Are you talking about the key contacts, or what? I can probably do the work with if you can give me some framework on how to do this.I have no desire to damage my baby.

Joe Edwards


No, the contacts are those 16 or so little straps that bridge the LCD module to the keyboard. The other display contacts to worry about are the rubber zebra strips that connect the LCD glass to the LCD circuit board... that is talked about in the HP41 service manaual.

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