Casio FX-201P, 202P & PRO fx-1: the trilogy

[Geoff Quickfall]

Just a light note,

It started with a non functional Casio fx-201P. Easy fix, corroded battery contacts. So full disassembly, cleaning of PCB and case then reassembly.

Then along came the PRO fx-1 with the cards. Fortunately there is a card manufacturer out there (see link below). Here is the thread on the Pro

CASIO PRO FX-1

Next the Casio fx-202p arrived in non functioning condition. No display, but power was getting to the PCB. Trouble shooting the PCB especially the electrolytic caps and I could not find any obvious problems, other then one corroded battery contact which was not the issue.

So I was testing the PCB further, continuity checks, solder joints and visually when I got called away. I did not realize I had left the ON switch in the ON position. Since there was no display reminding me that the ON switch was ON, I put the calculator on the trouble shooting desk. My next step was to remove and test the caps and replace all of them.

Well I came back to the calculator and realized it had been on for the last 5 days. Batteries completely drained. Installed new batteries with the intent to bridge the caps with appropriate caps as a test until I hopefully found the offending cap.

Selected the calculator to ON and without any further ado, it functioned with a crisp bright display. Tested the various functions including the continuous memory. All functions are perfect!

So, I can only imagine that it may have been one of the electrolytic caps which reformed over the few days that the switch was in the ON position.

Can’t think of any thing else but now day 5 since the “repair” and still perfectly functional.

1) Casio fx-201P 127 lines of code in semi FORTRAN.

2) Casio fx-202P same as 201 but with continuous memory supplied by two 357 button cells.

3) Casio Pro fx-1 same functions as other two but with card reader.