Any suggestions what to do when the A12 filmback advance the film only a half frame on a 553ELX ?
For the moment, I assume this problem happens whether there is film in your magazine or not and that it's fairly consistent.
So, the first thing I'd do is remove the magazine from the body and make sure the advancing gear on the right hand side of the back of the body operates when you release the shutter. You should see it go round (vertically) once returning to it's flat spot with a notch in it. You should also see should see the mirror cycle through completely along with the rear shutter curtains.
The other thing I'd try of course, is a different mag. if you have one, or just go to a local dealer and ask to try theirs. If it's really your magazine, and it's likely that it is, check to see whether the magazine kicks back from the camera when you release the shutter. That would indicate a gearing problem on the magazine. At that point, it's time to send it in for a CLA. And for that, I'd recommend David Odess in Randolph Mass. http://www.david-odess.com/
Take it light.