The fx-850P is a scientific calculator with a built-in library of 116 scientific formulas (also more complex ones like prime factorization). It is programmable in BASIC and even assembler.
This calculator was sold as broken because on the display almost the entire upper row, and also a few columns, were missing.
The model originally has 8KB of RAM only. The previous owner did a purely internal hardware modification that extended the memory to the maximum possible of 56KB.
Restauration Works
Checked the RAM modification, but found no error.
Attempt to re-glue the display cable with heat and mechanical pressure. I could recover all display rows (some have a low contrast though) and almost all colums.
Cleaned the case and keys. Polished micro scratches from the display glass. Fixed a bulge in the front plate that came from using a too long screw.
Reassembled the device, which came disassembled and with all screws in a separate capsule.
Known Issues
A few upper pixel rows and a few columns are still having a low contrast. The display cannot be repaired or replaced without conductive glue and special tools. I am concerned that further repair attempts might overheat the display cable and eventually break it, so I will keep it as it is now.
History
2022-02-05
Attempt to fix display by heating the glue of the FPC ribbon to the main board
