Casio fx-850P

The Casio fx-850P is a scientific calculator that is also programmable in BASIC (also assembler), and contains a built-in library of 116 scientific formulas (even more complex ones like prime factorization). The hardware can be extended through a proprietary port.

I bought this calculator at an online auction. It was sold as broken because almost the entire upper row, and also a few columns, were missing on the display. The previous owner also did an internal memory upgrade from 8KB to 56KB, which is the maximum possible.

Configuration

• Built: April 1987 (manufacturing code 7D608A)
• CPU: Hitachi HD62002A0
• Display: 2 x 32 alphanumerical (no graphics)
• ROM: 8KB
• RAM: 56KB (by a hardware modification)

Known Issues

• A few upper pixel rows and a few columns are still having a low contrast. I am concerned that further repair attempts might break the entire display, so I kept it like this.

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. Removed 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.