Today’s teardown target is an early 1990’s electronic organizer from Casio. Casio Digital Diary SF-4000, complete with a travel guide!
The height of components was high enough that they had to recess them inside the plastic frame!
With the board exposed- not a lot of surprises here: a Hitachi HD62023C50 processor, NEC D43256-10L low power 5V SRAM (70mA active, 100uA standby, data retention specified down to 2V), 2MHz oscillator and a power supply. The main membrane keypad is connected in the lower left, while the display and the upper keypad is going through a flex on top.The board is two layer and very thin- you can see traces from the back showing through.
The instruction label directed the user to replace batteries one at a time, so to keep RAM contents alive, there are MA151K diodes across each cells. That way with at least some batteries still present, memory contents is preserved.
Here is the power switch. It will be eerily familiar to those following along at home- the same design was used in a Soviet Elektronika MK-51 calculator we tore apart a while back. I think I know who cloned whom!
Even the footprint of the contacts is the same, with a minor detail- they are gold plated! MK-51 used tinned pads, good for probably a few cycles.
On to the top assembly:
The driver packages are rather strange- I’ve never seen anything like that!