Casio SF-4000 digital diary teardown

Today’s teardown target is an early 1990’s electronic organizer from Casio.  Casio Digital Diary SF-4000, complete with a travel guide!

Interesting mix of keys- membranes plus some hard buttons

Complete with a Travel Guide!

Very solid and compact unit

With the back cover off, and individual coin cell covers removed. Note brass inserts for the screws!

Plastic label peeled off

The height of components was high enough that they had to recess them inside the plastic frame!

Batteries are in series, but with taps brought out to allow replacement without loosing memory contents

Another view of the holder

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.

We have a serial port in the upper left!

Looks like the diodes are across each cells

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.

Diodes on all battery inputs, voltage regulator

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!

Something looks very familiar here!

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.

Unlike MK-51 clone, contacts are gold plated

On to the top assembly:

Two LCD drivers and keypads

The driver packages are rather strange- I’ve never seen anything like that!

The lead frame appears to be copper and soldered to the board.


10 thoughts on “Casio SF-4000 digital diary teardown

  1. tentei recuperar a minha casio digital diary, funciona em pleno, mas nao consigo trabalhar com elas por desconhecimento do seu funcionamento, preciso de um manual de funcionamento donde conste:
    – Gravar e apagar dados;
    – Tem o calendario de 1988, como actualizo?.

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