I got an email of someone whoes calculator Casio 880 is having troubles after changing the batteries, as it is a very common failure on Casio FX-880P and FX-850P, I write here the question and the solution.
Message: I cannot make the calculator work after changing the batteries, the TM, SN error codes appear, and nothing works. It does not even make an addition.
That problem is very common and easy to solve. First of all, I tell you how you should have changed the batteries in case you have not done it yet, to make you know by the next time.
The calculator has 2 big batteries (CR2032) that are the ones that make the calculator work, and a small one (CR1220) which is the one that saves the memory when the battery is changed. You have these different batteries to have a backup battery when changing, not to lose your information. Then you have to change just a battery, the big ones or the small ones, not the three at the same time. Once you are done with one, you can change the other.
To solve your problem, with the calculator turned on, push with a needle, the hole placed back, where the letter “P”. Doing this it will not delete the programs you have on the Casio, and I guess with this it would be enough to solve your problem. This button works to take away the static electricity.
If it does not work, you have to push with a needle the hole in the front “ALL RESET”. That will delete everything you have in the calculator.