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I tried to modify a old gcode uploaded through repeater to my sd but it look like unformatted/unreadable jam of symbol.

I used notepad, gedit, word and google doc for open it without success.

Any idea?

Why don't you open it in repetier again??

When i uploaded the gcode repeater can't redownload it; it can only start the sd print.

The strange is this, pc can't read but rambo work

Repetier by default uses a binary protocol, rather than the original GCode.
When you upload the file from inside repetier host the firmware converts it to this binary form during the upload.
Repetier firmware will read standard GCode files off SDCard, just plug the card into your PC and copy the file that way, it's also a damn site faster.

So there is no way to modify the gcode?

MarioMas wrote:So there is no way to modify the gcode?

Not easily no.