Failures in the calculator when changing batteries.

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.



37 thoughts on “Failures in the calculator when changing batteries.

  1. Dominique says:

    ok my problem is I was doing to many thing at once so I accidentally remove both batteries and erase the memories of the calculator so I need a way to reprogram my calculator and to make it work as new please need help cause their is no way to get in contact with japan for this model from the US thanks

    • javitopo says:

      Hi Dominique,

      You must do the post.

      -To solve your problem, with the calculator turned on, push with a needle, the hole placed back, where the letter “P”.
      -You have to push with a needle the hole in the front “ALL RESET”.

      Please confirm that the problem is solved


  2. Armando says:

    Hello, I’m Armando, I have problem with my FX880P calculator when I change the battery. After I chaged the two big battery then fixed it and close then I change the single battery, when I open my calculator then type 1+1 no answere instead it shows OM error Out of memory

    Thanks & Regards,

    • javitopo says:

      Hi Armando,

      To solve your problem, with the calculator turned on, push with a needle, the hole placed back, where the letter “P”. And also you have to push with a needle the hole in the front “ALL RESET”.

  3. ilias says:

    Hi all,
    i had programed my casio fx880p and used it for many years but somehow (maybe change of batteries) now i can not execute any program despite it indicates that still has programs in its memory(10 asterisks in basic mode). Is it possible to execute programs without losing them?

    • javitopo says:

      Hi ilias,

      If you do not change the batteries correctly In twice, backup battery CR-1220 and operating CR2032 batteries

      Calculator often fails, it puts asterisk in all programs and does not work well. It is able to do simple addition. If your calculator can not addition, you may not have the 10 programs have the error.
      please confirm.

      If this is the case, there is no solution, it must be reset and programs are lost.
      If otherwise perhaps if you can recover. Please tell me if it is able to do simple addition.


  4. ilias says:

    Dear javitopo,
    first of all thank you for your immediate reply. can you please tell me what do you mean by saying simple addition? addition of a new programm? because i can not do anything with programms. when i type mode 1 appears on the screen :
    P * * * * * * * * * * 0B
    As you see on the screen there is no programm ready to execute or access. As you also see free space is 0B. Is it possible to has been blocked and now it needs a password to unblock? The previous owner told me that he had for password : pass “10”
    but it doesnt respond to that password.
    Your response would be very helpful. Thank you in advance.

    • javitopo says:

      I refer to calculate 2 + 2

      I think the calculator has an error and is not able to calculate 2 + 2

      If I am wrong and the problem is a password I tell you how to remove the password.

      But first I want to know if it is possible to make 2 + 2


  5. ilias says:

    Dear javitopo,

    No i can not do any mathematic calculation. After typing 2 + 2 appears on screen : OM error
    I guess you are right my machine has an error. Can you tell me how could i fix this problem?
    Apart from making it calculate properly I want also to programme it again. I have the programms typped on a paper but i dont know how to start programming it again. As i told you before i can not do anything in basic mode. Is it easier to do this via pc? In that case i will need i cable and a software?


    • javitopo says:

      Hi ilias,

      To solve the problem you have to reset the calculator, but the programs were deleted.

      You must do the post.

      -With the calculator turned on, push with a needle, the hole placed back, where the letter “P”.

      Retry now 2 + 2 if you’re lucky and it works do not follow, the programs have not yet been deleted.

      -You have to push with a needle the hole in the front “ALL RESET”.

      Programming with the PC is more comfortable, also keep a copy in case there are problems you can refresh. this website is in English and Spanish, if you go to the Spanish version, there is a section of programs, I have many programs for free download.

      The problem is that they are in Spanish 😉 , but perhaps help you.

      If you need cable to connect the PC to tell me that I have available.


  6. Hugo Diogo says:


    I have replaced the batteries, and nothing works.
    I tried the P and ALL RESET buttons, but stil don’t work.
    Is anything that can be done to work again?

    Thank you,

    • javitopo says:

      Hi Hugo,

      Before changing the batteries working?
      The batteries threw acid into the calculator?
      When you put “POWER ON”, does nothing?

      Another problem is that some calculators dust enters the “POWER ON” key, you have to disassemble and clean the plate with alcohol. To find out if this is your problem you press the “POWER ON” key down a bit, to see if now on.

  7. JP says:

    I can’t calculate %, for eg. If I check 2% and by pressing EXE.. it’s showing SN error. I’m not getting the answer.. How to solve this issue? Kindly help me out please.

    • javitopo says:

      Hi JP,

      To solve the problem you have to reset the calculator.

      -With the calculator turned on, push with a needle, the hole placed back, where the letter “P”.

      -You have to push with a needle the hole in the front “ALL RESET”.


  8. Dave Nevado says:

    Hello to every one,

    I have a programmable calculator Casio FX-702P. I need a help to reset the unit becausethe LCD Screen shows a continuous character moving from right to left. Any key buttom to reset or stop the problem? When the character moving stop, a number :89 :>,Z $ Z appear. THank you.


    • javitopo says:

      Hi Dave,

      I do not know reset button on fx-702P


      Be sure to perform the following operations after battery replacement

      “MODE” “1”
      CLR ALL “exe”


      Please tell me if it works

  9. Dave Nevado says:

    HI to everybody,

    Thank you for your time and effort to answer my inquiry. I greatly appreciated that.I did the instructions given but it did not work. I do not know if I did it properly. I just notice the command F2 followed by T button refer DEFM in my calculator not DEFT.

    This is what I did

    1. Press MODE button then button 1
    2. Press button C followed by button L then button R, button SPC, button EXE
    3. Press Button MODE followed by Button 0
    4. Press button F1 followed by button comma (,)
    5. Press button F2 followed by button T then button 0 then button EXE
    6. Press button V, followed by button A, followed by button C then button EXE

    Did I make mistakes the sequences in instruction? Is there any key or button to press simultaneously in that instruction?

  10. Mr. Iceman says:

    Hello all,

    Just changed all 3 batteries, first time after I got the FX880p new some 30 years ago. I measured them after replacing and all were showing 3V+. Most importantly, all is working great.
    What I did was replace the small backup battery first, put it back firmly in place, then changed the 2 main ones. The big ones are more likely to retain some juice over time, and the small one is probably more likely to drain first. Hope someone might find this useful.

  11. Harshal says:

    Hi I have been using casio fx-850p since many years.
    I have loaded my program in casio fx-850p and it was working fine since few years. Suddenly, when I tried to open the program today, it started throwing FC error 5. Would you please help me on this error? I tried to reset but no luck

    • javitopo says:

      Hi Harshal.

      I do not understand because if the program worked well before now gives that error, you will have to look at line 5 of the program

      The number 5 means that it occurs in line 5 of the program
      The FC error is

  12. Harshal says:

    Hi javitopo
    Thank you very much for quick response. I was trying to say that program was working since long and after starting my PC few days in the morning, it started throwing FC error. May be my son played with it:) Would you please tell me how can I open the program and debug line 5?

    Big thanks

    • javitopo says:

      The program is on your FX-850P right? Or is it on your PC?

      If the program is on the PC, you can see it with any text editor such as notepad, word,…

      If the program is in the calculator
      “MODE” “1”
      “S” (Shift Red S)
      Press the program number (from 1 to 9)
      writes “EDIT” press “EXE”
      With the arrow down you can move through the lines of the program

      If you have it on the pc, you are free to send it by email to see if I detect something strange


      • Harshal says:

        Yes. It is FX-850P. Thanks for the response. The program is in Calculator. When I did the edit and exe. it started giving me PR error.
        By the way, when I entered into mode 1 (BASIC), it gives me P ******* 83338B. Is there any strange indication there? How can I move my calc program to PC?

        • javitopo says:

          P ******* 83338B
          That is not normal, when the calculator does that, you have to reset it to return to normal work, but if you reset you will lose the programs.

          You can try, reset only by the back, the hole that puts “P”
          Just by the back you will not miss the programs, but I do not know if it will be enough for your calculator to rework.

          To send the programs to the PC you can use the cable that I sell.

          But I do not know if you are going to be able to send the programs with the calculator in that state, maybe also error and nothing can be done until the calculator is recovered.

          Have you changed all 3 batteries at the same time? If you change the 3 batteries at the same time, or if there is no battery left in the 3 batteries, the calculator is put into that state.

          Must change in 2 times,
          1 time 2 CR-2032
          1 time 1CR 1220

          Test to add 2 + 2 will surely also give error, the calculator can not work in that state.

  13. javitopo says:

    Harshal but P ******* 83338B, it’s very strange, Sure that puts 83338B?
    An FX-850P can not have so much free memory, maybe you’ve put a number more?
    To try to know if you could pass the programs to the pc, try typing
    “MODE” “1”
    Type the keys SAVE”COM0:5
    (The previous thing to the 2 points is a zero)
    If you give some error you will not be able to send the PC with the cable, if it does not give error maybe it is possible
    Did you hit a pin in the hole in the back, the hole that puts “P”?

  14. ampervez says:

    Hi. I have bought a Casio FX-702P. The battery compartment was clean. I inserted new batteries and the machine switched on. I have tried the above method to clear the program areas, however the command VAC does NOT clear the system variables. If I assign a memory e.g A=10. When I check contents of “A” it gives ERR-6. I have tried increasing memories using DEFM (1-20), but I still get the same error. I have tried storing a number in other variables A-Z, but I get the same error 6. Is there a hardware/factory reset or software reset for the FX-702P ?

    • javitopo says:

      Hi ampervez,

      I’m not sure if you have. Have you tried this?

      “MODE” “1” CRL ALL “EXE”
      “MODE” “0” “F1” “sac/,” “F2” “T/DEFM” “0” “EXE” VAC “EXE”

      Please comment on the result.

      • ampervez says:

        Hi javitopo. Thank you for your reply. I have already tried this. The variable seem to be stuck. If I enter “A=10” {EXE} the calculator cursor returns. Then when I enter “A” {EXE} the calculator responds with ERR-6. The same thing happens whatever variable (A-Z) I choose to store any number.

        If I enter a program in P0:
        10 INP A
        20 PRT A

        When I RUN it and enter a number, the calculator stops with error:-
        ERR-6 IN P0-20

        The same error occurs if I use any variable (A-Z).

        Your help much appreciated. Thanks.

        • javitopo says:

          Hi ampervez,

          Sorry for taking time to answer, I’ve been very busy.

          I don’t know how to help you, I don’t know how to solve it.
          I’m not sure if I have an FX-702P now, over the weekend I’m going to look to see if I have any and do the same tests as you, to see what happens.

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