Electric type writers

Working on an ol ax-325 electronic typewriter.
All keys are working except three letters..
M,K and F...
Why???
Can someone help???

Is it a golf ball, wheel or thermal machine?

I Googled the ax-325 and it seems to be a daisy wheel printer.

Does Venantius mean that pressing those keys results in no hammer action or that these letters don't print? Could these three letter arms be damaged or broken off?

first question: when those keys are pressed, do the print wheel and hammer solenoid respond, or is the mechanism not responding at all to those keystrokes?
if the mechanism responds, you probably have broken teeth on the print wheel. if nothing happens at all, you may have dirty or defective keyboard switches.