Electric blanket internal disconnection measurement circuit

Find the circuit for the internal disconnection of the electric blanket. The working principle is: M spot welding has a wire of about 2cm as the inductor. When the inductor
is close to the live mains live wire side, the induced voltage is rectified by VD and changes
from VT1 to VT3. The composite tube is amplified and added to the base of VT4
to turn on VT4. LED light display: When the induction body is far away from the live wire or the live
wire is not charged, because there is no induced voltage VT1-VT3 has no output, VT4 cannot
get the bias current and is cut off, and the LED goes out.
    Component selection and fabrication are as follows.
    The value of the triode g>20, Ieeo is as small as possible; the light-emitting diode I. ED
can choose any model; the value of resistor R is generally tens of ohms, and RP is a semi-variable resistor.
    During debugging, the induction body (induction test pen) should be placed close to the live wire, and the resistance of RP should be changed to make the LED go from extinguished to illuminated. And when
leaving the line of fire, I. ED should go out. When
    using a test pen to check the electric blanket , you should disconnect any of the two joints of the heating wire and the power cord, wrap the disconnected wire end with an
insulating wrapper, and then insert the side of the power cord plug connected to the resistance wire into the live The live wire trapping hole (to prevent electric shock, you can also string a small capacitor with sufficient voltage resistance
), so that the induction body of the electric test pen is close to the electric heating wire, and search sequentially from the end that is not disconnected. Once the LED goes out, you have found it. The break.