Today we have a teardown of a Soviet calculator Elektronika MK 51( Электроника МК 51) for those familiar with the language. It was bought new in 1993, worked (sorta) for a few years and just drove me absolutely nuts with its lack of any reliability. The design is supposedly a clone of Casio FX-2500
Taking two screws out, the back cover (a stamped metal piece) is removed and we see the board, with obligatory red solder mask
Taking a bunch more screws out, the board slips out of the case, leaving keypad and LCD in the plastic holder
Pretty standard buttons, relying on a membrane with conductive surface to make contact. Note the sliding switch contacts in the upper right. The hot melt plastic holding it was a very typical failure point. So were the conductive coatings wearing out on the rubber keypad .
The slide switch was a really weak point of the system. The spring contacts sliding over solder coated pads did not take long before intermittent connection developed, causing random reboots.
Moving on to the display (part number ИЖЦ2-9.7 with a 1992 date code), it’s a transmissive glass panel, with a separate polarizer film installed in the case in front and a reflecting sheet behind. Pretty standard Zebra strip (another source of many troubles in this model) connects things to the board:
And finally, for those curious, here is the schematic:
Update: I’ve attempted to power it and see what happens. Well, it does work, as long as somebody continuously presses on the back of the board near LCD Zebra!