Ferrite core transformers and inductors are in just about everything these days. Unfortunately ferrite is a very brittle material and components with ferrite cores are often coated with varnish which makes them very difficult to disassemble without breaking the ferrite.

In the past I've used caustic solutions as well as dichloromethane based paint remover to successfully remove this varnish coating but this isn't without its own problems.

The caustic solution can take many days to work its way right into the bobbin and can change the surface finish of some plastics used in bobbin construction. It is however easily washed from the treated parts and exposed skin with just running water.

Dichloromethane, while much faster than caustic, is much harder to handle safely and can be difficult to remove from the treated parts and from skin if contact is made.

This is the main transformer from an ATX switch mode PSU and they are pretty much all very similar if not almost identical to this.

Older power supplies usually switch at a lower frequency and have larger transformers for the same power output. These will generally have two E cores that meet in the middle of the bobbin.

Newer power supplies switch at a higher frequency and have much smaller transformers. While some of these will have two short E cores most of them have one E and one I core, the I core usually being on top of the transformer.

There is just a few simple steps neded to prepare the transformer for boiling and disassembly. Firstly the common wire is bent upward and the sheath slid off to make a convenient handle that will protrude from the water and make the transformer easy to remove from the saucepan when hot.

Where there is no convenient wire to use to lift the transformer it is a simple matter to solder a length of wire to one of the pins for just this purpose.

Nearly any old length of wire will do, solid, stranded, insulated or bare. It just needs to be strong enough to lift the transformer and long enough to protrude from the water.

The, usually yellow, tape that wraps the core pieces also needs to be removed before you put the part in to boil.

It is really inconvenient to have to remove this tape from a hot, wet part.

While this method doesn't use any harsh chemicals there is still plenty of opportunity to hurt yourself. To avoid this you will at least need some thick, waterproof gloves, such as these heavy duty garden gloves.

The parts should be put in the saucepan and water added until the cores are fully submerged. The saucepan and parts should then be put on to heat.

Don't put cold parts into hot water, this is an almost guaranteed way to break the cores.

Also it is probably inadvisable to use the saucepan for cooking after using it for this. At best it will make things taste a bit odd.

Once the water is boiling it takes very few minutes for the varnish to soften. It is easy enough to remove each part and give it a try and, if it doesn't release, to replace it for a little longer.

The smaller the part the quicker it will be ready but even the larger parts shouldn't take more than five minutes.

Here you can see two, small, EI cored transformers successfully disassembled.

Once the cores have been removed from the bobbin the transformer can be left to cool. There is still varnish stuck to the core pieces and the bobbin but this can be removed mechanically or with chemicals once the windings have been removed.

Sometimes, no matter how carefull you are, cores will break. It may not have been anything you did, if the PSU was handled roughly in the past the core may have been broken before you even removed the transformer.

Even transformers with broken cores can be reused. As long as the pieces are a good fit when they are assembled the transformer will still work. In use the magnetic field will help pull the pieces together.