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Calculator buttons except ON button don't work in FX-991W

Buttons not working

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#1 Thehumancalculator



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Posted 02 June 2022 - 10:50 AM



I have a Casio calculator from 1998, Fx-991W. Since recent one month, it started to have a strange problem.

All buttons on the calculator except the ON button don't work. Sometimes only some buttons work and calculations are wrong.  However, if I put the calculator in the sun for 15 minutes or heat it slightly to about 40C for five to ten minutes  and then switch it off and switch it on again, the buttons start working. The calculator then starts functioning normally.  This calculator served me for twenty years.


Is the IC in the calculator bad or does it have water or moisture in it which needs to be dried by cleaning the PCB?  I've already changed the battery recently.


I'm curious what is the solution other than buying a new Casio scientific calculator.


Any engineer can offer their opinion or insights into this problem. Below is image of the calculator.






Edited by Thehumancalculator, 02 June 2022 - 10:55 AM.

#2 siealex


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Posted 17 June 2022 - 08:54 PM

Water under PCB.

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