Hello, Giancarlo;
I met a Giancarlo at Universidade Católica de Petróplis in the late 80's. Would that be you?
The HP41 series has two basic types: the fullnuts and the halfnuts. Unfortunately I have no provider to hold my pictures anylonger so you could see a picture of them both. I'll send the picture to your e-mail if you wany. As a reference, please, take a look at your calculator's LCD and check if there is a black frame with rounded corners around the LCD's actual viewing area. If you see this black frame, yours is a halfnut-type. If the display has no frames and 90-degrees angles at the four corners, yours is a fullnut.
In the halfnut type, Jeremy's description is correct, but there is a big "hill" to climb: accessing the LCD's assy mean removing all (heat-molded) plastic rivets that lock the keyboard to the upper half-case, and the halfnut's LCD assembly contains not only the LCD's driver circuit, but also the ROM and RAM chips. Handling it demands extra caution and I have never disassembled a halfnut LCD... so far.
If yours is a (somewhat rare) fullnut HP41CX, LCD assembly is a separate module that is soldered in the keyboard and you may have just to resolder it. I can guide you in the second case.
Feel free contacting me if you want to carry on. As I live in Brazil too, we may arrange your HP41 maintenance here. (I have at least six different models in my workbench right now...)
Best regards.
Luiz C. Vieira - Brazil
(if you e-mail me, you can -surely- write in Portuguese...)