The same customer that brought in the Royal Quite De Luxe also had us tune up this classic R.C. Allen adding machine. The adding machine had sticking keys, would not clear totals and could not subtract. When I opened up the cover I discovered the selectors were not connected to the negative bail mechanism. Mr. Montgomery recommended I consult the R.C. Allen service bulletins. Sure enough, there was a known problem with the subtraction mechanism.
I will not bore you with the gory details, yet… maybe I will (cue evil laughter). After consulting the amazing descriptions in the service bulletin it appears that if a person completes a cycle with the handle when the negative bail hangs up, it bends the part that controls the subtraction slide. Of course the solution back then was to order a new part!
I also noticed that the spring was missing from the positive power cam connecting the negative power bail that drives the subtraction mechanism. What was there? A small spring attached to the frame. I think the original spring broke causing the negative action bail to bend, a repair technician tried to bend the part back into place and with out the proper size spring, just attached a replacement to the nearest spot. Well, maybe it worked for a while.
Fast forward to this day. I replaced the spring with the type in the service guide, got the selectors to contact the negative bail rod, and could not get the broken part to bend back far enough to allow the subtraction slides to move. Sometimes you bend a part too far, and POP! Broken. It is these moments when I wish for more parts machines. At least addition works, and the totalizer now clears after a completed operation.