Casio SF-5990SY Repair for Use in Teaching

While looking for a old electronic gadget to use as a role model to teach my younger sibling about memory addressing and bus sniffing with logic analyzer, i came across this unit in a garage sale and decided to take it and see if it would work and luckley it was what i was looking for.

Finding it wasn't the only challenge, the device wasn't working and needed some repairs.

Material:

Solder;

2x20cm twisted pair wire;

1 x 1x4001 diode;

Tools:

Soldering Iron;

31 in 1 screwdriver kit;

fine grain sandpaper;

The first step is to power the device and see how it behaves.

while opening the AAA battery compartment there was a surprise the all the terminal were crossed to oblivion. To solve the problem was easy just connecting two wires in the connecting two wires in the solder pad of the battery terminals.

The unit had a shorted diode, i changed it with a 1n4001 and the problem was gone, the original diode doesn't have any marking for identification.

Finally the i managed to power the device.

Due to liquid entering inside the unit, the keyboard was damaged not a single key worked, the solution was simple cleaning the thin metal oxide coating all the key contacts. For this purpose a fine gran sandpaper was used to shave off the oxidation layer and some water to clean the dust out.

The final step is to close all the uit back to its almost original state.

The top case of the main logic block will remain opened to facilitate the access of the pcb for probing to demonstrate how old computers data and address buses work and how to hack to attach external hardware throw them.