On Fri, 22 Nov 2019 22:34:01 -0800, whit3rd wrote:

It's either an energency overtemperature cutoff (like a fuse), or a
thermal switch that repeatedly time-cycles according to the
heating/cooling time constant of its companion resistors.

I assumed it was tucked between those resistors to sense any higher than
usual warming in them. It's marked 76 degrees C in the case of this one.
I'm guessing it (since it's in series with the live line) that if the
temp rises above that level it will wind back the current, but this one
has blown completely open-circuit and maybe that's what it was designed
to do. Nothing visible, just on testing for resistance.

The diodes presumably send current to heating element A on positive
half-cycles, and heating element B on negative half-cycles (so as to
retain some function if one element fails open-circuit).

Sounds feasible. I'll check the resistance of the heating elements and
see what they show. One may have gone partially short-circuit, causing
the fault in the first place. It's a 70W blanket so at 240V they should
come out at about 800 ohms in total if my quick 'n' dirty sums are
correct.



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