The remote tab setting and clearing on my SM4 was drifting into the arena of the unreliable; every now and then tabs were not set at all.  Something needs mending!

A patient minute or two sitting and looking at the back of the machine revealed how the remote tab mechanism was intended to operate.  There is a rack of tab teeth which can be either in the up or the down position.  Pressing the ‘+’ (tab setting) key moves the upper actuator (‘A’ in the photo) downward, and it is supposed to push one of the teeth down at the same time, where that tooth then acts as a tab setting.  Pressing the ‘-‘ key pushes the tooth up again to clear that tab, via another actuator under the rack of teeth (marked ‘B’). 

Which tooth is moved depends on the carriage position.   On my machine, these two actuating levers were sliding past the tooth that they were meant to move; the rack of teeth and the two levers were not in proper alignment with each other. 

To cut a longer story short, the two screws marked ‘x’ in the pictures allow the whole rack of tabulator teeth to be moved together, and a gentle adjustment of the position of this rack, with those two screws just loosened, enabled rack and actuators to be aligned once more. 
Now everything is fine again!

Getting over my feelings of extreme cleverness at having done this, I soon realized that there are probably a whole cartload of checks and alignments that are meant to be done when adjusting this mechanism, but in the absence of a fettling manual for this machine, I merely guessed by eye that everything was straight and true before finally tightening the screws.  If anyone has any tips or other information, please tell.
 
Hopes this helps!

Last edited by beak (21-12-2013 03:37:37)