Help figuring out suitable resistors for electric blanket controller

Thread Starter

Hnaam

Joined Oct 12, 2022
2
Been racking my brain trying to figure out how this circuit works but I've just accepted its beyond my understanding. I need to replace resistors R1 and R2 as they're both open. Is there any way to figure out what the values of these 2 resistors should be? The blanket is made for 240v AC. Also F1 is a thermal fuse which I have a replacement for.
Front-reverse board.pngPlug.png
 

Ian0

Joined Aug 7, 2020
6,660
First, I suggest figure out what fault in the blanket caused them to fail, before you kill someone with a faulty electric blanket.
 

Thread Starter

Hnaam

Joined Oct 12, 2022
2
First, I suggest figure out what fault in the blanket caused them to fail, before you kill someone with a faulty electric blanket.
The controller is from an identical blanket which was faulty. Thats been disposed of.
 

MisterBill2

Joined Jan 23, 2018
13,689
The concept of replacing what might be a temperature sensor for an electric blanket is rather unsafe, given that it is a powered heating element acing in close proximity to a sleeping person.
So I suggest learning exactly how the controlling is done before making any changes..
 
The concept of replacing what might be a temperature sensor for an electric blanket is rather unsafe, given that it is a powered heating element acing in close proximity to a sleeping person.
So I suggest learning exactly how the controlling is done before making any changes..
Agreed, R1 & R2 are current sensors, positioned very close to the thermal fuse. Critical for safety. My diagram has an error, they should be labelled 18k. In circuit measurements were slightly lower. I'm still confused about the LED current paths, purely academically! The controller will be in the bin shortly!
 

MisterBill2

Joined Jan 23, 2018
13,689
I struggled with that circuit also, but possibly one of the diodes #5? is a zener that conducts with a voltage drop in the reverse direction.
 
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