About the new trimmer, I have to say that what you can see in the pics was only a trial. :)
My technician followed almost all your instructions, but he didn´t get, at first, a good result. After adjusting the original trimmer, the characters were shown on the display, but they were only visible if you watched from a certain position (about 45 degrees above the display), but not if you´re placed in front of it. So he thought maybe athe new display needs a higher power trimmer to get a higher margin in relation to the degree of contrast. The one shown in the pic is 10 while the original is 5 (forgive my ignorance, but I do not know if this relates to volts or other electrical measurement). Now that we know it works, it will put a new trimmer, yes, this time soldered to the PCB. :)
Thanks again for your help!