Mixers, blenders and coffee grinders

This page covers several types of kitchen equipment such as mixers, blenders and coffee grinders where the action is principally mechanical. It may also be applicable in part to bread makers and even electric toothbrushes.

Summary

The class of domestic kitchen electrical appliances which which mix, chop, grind or liquidise (or a combination), invariably contain an electric motor. Problems can arise with the motor, or the associated electrics, or some purely mechanical issue such as food residues getting to where they shouldn't. Dissassembly can sometimes be challenging, but if you can get inside then the problem will usually be fairly easily seen or diagnosed with a multimeter.

Safety

Most of these appliance run off the mains supply, which can be extremely dangerous if you don't know what you're doing, especially in the presence of water or moisture.

Some contain quite powerful electric motors, often with sharp blades attached, and even the less powerful could cause a nasty injury if fingers, loose hair or clothing got entangled.

Mechanical Problems

Spindles and seals clogged with grease or food are very common. This may cause a jam which you can hopefully resolve with cleaning. Make sure any solvents or cleaning agents you use are food safe, or thoroughly rinse before returning the item to use.

Seals can leak, and this is often more problematic. Cleaning might resolve the problem, or there might occasionally be an O-ring you can replace, but once water or contaminants get into the works the chances of a successful repair are greatly reduced.

Cracked mixing bowls or jars may not be easy to repair as it will be hard to clean any contaminants from the crack, which may have become home to bacteria. You will need to clean and roughen the plastic in order to get any adhesive to stick, but if you can do that then 2-part epoxy resin may give a successful repair.

Motor problems

Devices of these types invariably use a universal or AC/DC motor, which provides a high starting torque. If you're not familiar with how these work, check out the Electric Motors page.

If you carefully inspect the wiring within the motor you should find that the current passes from one terminal through each of the field windings and the rotor (via the commutator) all connected in series. Using a multimeter (How to use a multimeter) check the resistance of each of the field windings and of the rotor. If either of the field windings shows as an open circuit then that is the fault. It could be a fractured wire or the winding could have burned out (in which case there are likely to be signs of overheating). In the case of a fractured wire the fracture may well be hidden, and even if not it may be very difficult to access or repair.

Look out for a thermal fuse. If you're unlucky it may be burried in the field windings, impossible to replace or even to see.

Check out the commutator and the brushes. The brushes may be worn and in need of replacement and the commutator may need cleaning with isopropyl alcohol.

Electrical Controls

First of all, check the fuse and check the mains lead for wear or damage. There may be a fuse within the device as well as the one in the plug. If you can see a thermal fuse, check that too.

There will often be some kind of safety interlock to prevent the device operating with blades or other moving parts exposed. There may be a mechanical problem with this, or with a switch associated with it. This may be a microswitch. These come in a small selection of sizes but with a number of variations. Nevertheless, replacements are easily obtained.

Faulty switches are fairly common. These may well be standard parts that you can find replacements for online. You may be able to disassemble a switch, but beware! They often contain a small spring which can take flight, a ball bearing that can roll away, or other tiny parts which fall out. Working out which bits go where and how to hold them in place during reassembly can be challenging.

Electronic controls can be subject to all the same kinds of faults as any other electronic device. Check for failed capacitors, or any other devices showing signs of overheating.

Many of these appliances provide motor speed control, sometimes with a fully variable speed or several speed selections. Usually, a universal motor speed control will use a diac-triac arrangement to control motor speed. Either the triac or the diac can fail, but it is often the diac which has failed and the common sign of that is that the motor will run at full speed, but not at any reduced speed. See How dimmers and motor speed controllers work for their theory of operation and how to fix them.

External links

Consult Kitchen Appliances at:
Repair Café

Consult Mixers at:
iFixit

Consult Blenders at:
iFixit

Consult Coffee Grinders at:
iFixit