Mitsubishi PLC FX3GE Symbolic Info loss

I am trying to make a change to a Mitsubishi plc FX3GE program that is running currently in the machine.

I do not have a copy of the original program.

When I try to upload, it gives me a warning message saying it was unable to convert/upload the symbolic info from the plc as the program was written in FB.

I then tried to create a new blank project with project language as ST/FB, but in this project, I am unable to upload the program in this type of project. Only the download option is available.

I want to edit just one rung, is it possible for me to make changes to this rung and download only the change and not the entire program?


I tried to make change online but when I tried to download the change I made, it gave me a warning message saying the project on the PC has a part that is an unconverted program that will replace the symbolic info that is currently running program in the plc. If I do ok will my program work normally or not, if I did download this unconverted program part with the reset of the program.

Any info on this topic will be helpful.


Thank you,
Ghanshyam Z.

Original programmer didn't download Symbolic info, so now there is no option to do it. When you upload you will have application without symbols/labels/definitions, all in one program.

Goghie is right, without the original source code and no symbolic file downloaded, it will come back as simple ladder with no comments or symbols.
The other thing is it will not exactly be one long ladder but a main program with a FEND instruction (this is the main scan program), after that there will be code in what could be called sub routines with jump labels & RET instructions, also there will be a number of high end variables i.e. M9890 or D9700 etc. that have been used as temps (selected at compile time)so when a function block has been called, these high end addresses are used to pass variables to functions, & pass information back to the main program.
See attached pic, this is a function block & the compiled code, note where the variables are copied to those high end addresses then a call to the subroutine & when it returns the result copied back to a variable.

parky, so what happens if I make a small change to this uploaded program and download it back again. Will it work the same as before(other than the small change made)?

Will the converted FB work the same way as the FB?

Will no symbolic info affect the operation of the program once downloaded? Can I download without symbolic info as ladder?

Or it is not a good idea to try to make a change to this program?

There should be no problem providing the program you uploaded compiles before download, if I was you, I would look through the whole program manually & check there are no errors i.e. un-connected rungs (I do know that the older GXIEC IDE if the code was read back could have what is effectively broken rungs in it although the code would work if using GXDeveloper set to LIST mode, I suggest you upload the program plus the PLC Parameters & the memory (MAIN) and save it as a backup of what is in the PLC including any data that may be stored in the "D" registers, perhaps make sure the plant is not operating and is in it's normal start position. It may be important to save the status of the data memory because if you lose the battery or have to replace the PLC downloading just the program it may not have any values that the programmer may have set in retentive memory.
So, although not guaranteed but pretty sure it would be ok, upload everything you can (tick all boxes except the symbol & possibly comment upload), save the file as a way back should things go wrong, ensure it compiles (it may already have the info that it has, to be sure just add one contact in a rung, compile it then take it out again & re-compile), then do your changes & download. I'm sorry I could not guarantee nothing will go wrong but not being there etc.... makes me need to give no guarantees.
If you like, send me a PM with your email address & i will respond with mine & you could send me a zipped copy of the uploaded code, I have an FX3U
so could look at it, convert it & check there is no problem with the actual code compile (I do appreciate some companies do not like non suppliers handling code but the offer is there.