2015's calculator anniversary - the SR-52

[jebem]

Small update on Keyboard dismantling.

Well, the IC legs are too short to be inserted on sockets, so they will have to go back to their original positions in the PCB.

Meanwhile, I saw some marks of corrosion at one of the edges of the keyboard.
Also one of the previous owners had the keyboard connector re-soldered, and in the process they broke the supporting plastic frame.

Removing the adhesive plastic film revealed the PCB routes.




It was an opportunity to draw the KB schematics, by using direct observation and with the help of an ohmmeter to check the connections.

The circuit traces presents about 90 Ohm per cm. The longer circuit traces measured more than 1KOhm.



After some head scratching trying to make sense of the above circuit, finally the Texas design was revealed.
The KB matrix uses 6 Rows per 10 Columns for a total of 60 keys, where 45 key actually were used.