[Dave Moll]

Not being able to read Chinese, I am left with just the pictures. Without intelligible words, I find pictures alone difficult to follow.

I can confirm from experience the importance of clean dial contacts, as a thin layer of (non-conducting) oxidation that is easily overcome by line current can look open-circuit to the much smaller currents within the electronics of an internal tone pulse-to-converter such as a Rotatone. Stand-alone converters such as Dialgizmo do not rely directly upon the dial contacts, presumably operating by detection of the break in loop current.