I don’t know whether the power unit is the most important component of a computer system, but I’m sure its ‘s a  component without which your system wouldn’t work at all. In desktop computers power supply is realized as a metal box with many different colored wires coming out of it. This box is usually mounted inside the computer and contains a circuit board with a pulsed voltage regulators providing power to different cables depending on their color.On the other hand, these cables are connected to the various components of the system like motherboard, hard drive, DVD, floppy, etc.

Unlike desktop computers, laptop power supplies (also called adapters or chargers) are much smaller because for the laptop computers the most important thing is mobility, and mobility requires components with smaller dimensions. Therefore, in addition to being smaller, they are also implemented as a separate unit located outside the body of the computer, which is the main difference between the two types of power supplies. Another significant difference is that the laptop adapter uses only one cable to provide power (usually between 18-20 volts), which is then distributed to the various hardware components by voltage regulators located on the motherboard of the laptop. Otherwise, more cables would make the use of such devices extremely uncomfortable and also would have bad effect on mobility. But mobility is associated with motion, which sometimes causes damages in mobile devices and therefore here I will try to describe one of the most common failures in the laptop power supply units that occurs in their power cords and connectors.

As you may know, the weakest point of every power cord is the connection point with the connector, or in other words – this is where the cable bends the most. When I say ‘power cord’ I mean the DC cable which in most of the cases is difficult to replace, because one of the ends is soldered to the circuit board of the power supply.On the other hand, the AC cord can be changed easily, as there are connectors on both ends. On the picture below you can see both points where the cable could break most often and if you think that the time to throw away your adapter hasn’t come yet, then I think that this guide will help you continue to use it for a long time. For the next example I will use the power adapter from Fujitsu Siemens laptop with output voltage of 20 volts. Let’s see.

If the cable is damaged near the DC jack, it can be easily repaired in few steps, but you will have to cut the cable and replace the old connector with the new one, as the old will become unusable. This is because most likely the original connector will have a molded casing on it and the only way to remove that casing  is to break it.

1.Find a suitable connector. This is perhaps the most important task, because different laptop manufacturers use different connectors. Most laptop models use the so-called coaxial cable connectors (or also barrel connectors) as the most common plugs are 5.5 mm in OD (outside diameter) and 2.1 or 2.5 mm in ID (inside diameter). Their length varies from 8 mm to 14 mm. but the length is less critical than the diameter. Just remember that longer plug is not a problem but a shorter one may not be able to contact properly with the DC jack.

Remember also that some manufacturers such as DELL, Toshiba, SONY and HP also use more specific connectors, which are difficult to find on the market and most likely in such cases you will need to replace the entire adapter.

2.Prepare the wire.Cut the cable off about 10-20 mm. from the DC connector. Most power adapters have a large choke mounted near the connector, designed to stop the RF interference passing through the cable. If the choke is too close to the connector you can just cut it off. Do not worry, in most cases this would not affect the normal operation of the laptop.

3.As you can see the cable running from the power adapter to the laptop is a shielded coaxial cable. Strip the cable by removing about 20mm. of the outer sheath and twist the wires of the braid shield together. Inner conductor should also be stripped, but in order to avoid the risk of short circuits you have to cut only a small part of its isolation. I think 5mm. will be sufficient for wire to be properly soldered to the connector.

4.Now it’s time for soldering but first make sure that the shell is placed over the wire and faced the right way before making the connection. Some technicians also prefer to tin the wires first by applying a thin coat of solder before soldering to the connector.

5. DC connectors usually consist of two parts – plastic (shell or cover) and metal (the part that fits into the DC jack of the laptop or also called barrel). On the other hand, the barrel consist of two contacts. The outer, which is most often called the sleeve is the negative (GND) contact and the inner one called the tip is the positive (V+)  contact. Important: Be sure to solder the inner conductor of the cord to the positive contact and the shield to the negative one.

Sometimes, however, in very rare cases the manufacturer may swap the polarity of these two contacts, so before you start the repair it would be best to read the technical specifications of your power adapter. If you can not find such information, do not worry, there’s an easier option. Just look for the following sign on the body of the adapter.

Here it  says that the inner conductor is the positive one (V+).

Now let’s see how to fix the cable if it is damaged near the body of the power adapter.

1. In this situation, your task becomes a little more difficult, since almost all adapters sold in the market are permanently sealed by the manufacturer (i.e. manufacturer has not provided the option for disassembly and repair). This means that you must cut the body of the adapter in order to access the circuit board. You may also need to desolder the shielding cover that covers the board.

2.Once the two parts are separated, you can cut the cord. The most important thing here is to make sure that the point of failure will remain in that part of the cable which is soldered to the circuit board. To be sure just cut the cord off about 5-10 cm from the body of the adapter, because as already mentioned failures occur most often in that part of the cable. The reason is that sometimes the rubber grommet fixing the cable to the adapter housing is too hard, causing bending of the wires in one certain point. See above picture.

3.Prepare the cable in the same way as you did above, before soldering to the connector, then remove the unnecessary part of the cable. Make sure to remember the location of the two wires, because an incorrect soldering would damage the adapter or even the laptop.

4.Now you can solder the wires to the circuit board, but before that I recommend you to install a rubber grommet, that will prevent the cable from excessive bending.

5. Assemble the adapter. The easiest way to fix the two parts of the body is using duct tape.