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Archive for August 5th, 2016

Kenmore Model 158 Power Switch: Laying-on-of-hands Repair

The power switch on Mary’s “embroidery” Kenmore Model 158 sewing machine became exceedingly stiff, to the extent she said it was painful to push. Buying a shiny new switch seemed iffy, because a cursory search through the usual reputable electronic suppliers suggested there’s no way to specify how stiff the button might be, nor how that might feel in actual practice.

The switch harvested from the pulse-drive machine felt somewhat less stiff, so I decided to (try to) loosen it up and, if that worked, swap it for the stubborn one.

A pair of rivets hold the two halves of the switch together, obviously intended as a permanent solution. A carbide burr in the Dremel tool dealt with them easily enough:

Model 158 Power Switch - grinding rivets

Model 158 Power Switch – grinding rivets

Inside, the actuator drives a rotating brass contact:

Model 158 Power Switch - rotor

Model 158 Power Switch – rotor

Two stationary brass contacts are spot-welded to the wires:

Model 158 Power Switch - contacts

Model 158 Power Switch – contacts

The actuator under the button consists of a helix-twisted steel rod, a rather stiff spring, and a four-vaned phenolic blade that engages those two little flaps on the rotor. The rivet holes exactly fit plain old 1-72 screws:

Model 158 Power Switch - actuator stem

Model 158 Power Switch – actuator stem

Not seeing anything obviously fix-able inside, I wiped the excess oil off and reassembled it in reverse order:

Model 158 Power Switch - reassembled

Model 158 Power Switch – reassembled

Astonishingly, that bit of attention loosened it up: the button now presses easily!

I swapped it with the too-stiff switch and declared victory…

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