Toasters

This page covers toasters

Summary

In most modern toasters , the mechanism that allow for the toaster to work is triggered by the user pushing down the lever, provided that the toaster is plugged in and the power is on. Lowering down the lever closes the circuit and permits electricity to run through , it charges the electromagnet with current and thus holds the lever down for a period of time determined by a timer inside the toaster.

First let’s find out whether the toaster still get hot : when the toaster is plugged and you press the handle maintaining it at the bottom does the toaster’s inside resistances light up and the toaster starts to get warm.

Safety Warnings

Please take extra care when disassembling the device:

• Double-check it's not still plugged in when you open it
• Never poke anything in where the toast goes if it's plugged in
• Handle with care as it might still be hot

Principles of operation

In all toasters, you press the handle down against a spring to lower the toast into the toaster. This closes a switch allowing the electricity to pass through the heating element, and at the same time activating the timing mechanism. There are basically 2 types of toaster.

• In some, particularly older ones, the handle is held down by a latch, released by an electromagnet which is energised when the time is up. Usually, a bimetallic strip is placed close to the heating element and this bends as it warms up until it closes a circuit, energising the electromagnet.
• In other toasters the handle is held down by an electromagnet which is energised while the toast is toasting. An electronic timer circuit de-energises the electromagnet after the correct time, releasing the handle.
  • In all modern toasters the electronic timer uses a microcontroller. If it fails it's very unlikely that you could correctly reprogram a replacement microcontroller even if you could identify and source one.
  • Some older electronic timers use a much simpler circuit based on a commodity timer chip such as CD4060B or CD4536B. If you've eliminated other faults as far as you can you may be able to find a replacement chip by noting the markings on it and searching eBay.

Disassembly

The screws to remove the external cover are usually situated at the bottom of the toaster so you might want to turn it upside down. Once unscrewed take extra care around the area where the handle is as it can hold the circuitry for the on/off display light as well as the timer , and you don’t want to tear any wires apart.

Simple Faults and Repairs

Handle doesn't stay down

When the handle won’t stay down, it might be due to the electro magnet not working as it should.

Sometimes cleaning up the area around the handle as well as the electro magnet itself using compressed air and some IPA is enough to get the magnet back working as normal.

Handle / Toast won't pop up

When the toast wont pop up, it might be due to the timer being at fault.

Some toasters used to have a bimetallic strip which bent as it heated up and so triggered the pop-up when the toast is ready.

Some toasters charges a capacitor that acts as a timer and when reaches a certain voltage cuts of the power that goes through to the electromagnet which releases the handle. It might be a faulty capacitor in this case that prevents the toaster from popping up.

External links

http://home.howstuffworks.com/toaster.htm