Posts: 4,027
Threads: 172
Joined: Aug 2005
Hi;
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
Posts: 1,788
Threads: 36
Joined: Aug 2007
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.