Fix Faulty Electric Blanket

A friend asked me to look at her electric blanket controller, which was suddenly "dead". I removed the four Torx screws and opened up the plastic housing to look at the Printed Circuit Board.

At first glance it was obvious that two resistors had burnt out. I measured them with a multimeter and they were open-circuit. So was the thermal fuse in between them.

I desoldered the two X0405MF thyristors, too, and tested them in a unit that I'd bought via eBay. They tested OK.

The resistor values were unreadable and they, and the thermal fuse, were obviously safety-critical parts. I had no idea whether they had failed because of a mains voltage surge, because the blanket itself was faulty or because of a design fault.

Bearing all this in mind, I declined to replace the components and advised my friend to buy a new electric blanket. Safety always comes before profit.

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