1、 Maintenance example of laptop power adapter without voltage output
When a laptop is in use, the voltage rises suddenly due to the problem of power supply line, causing the power adapter to burn out and no voltage output.
Maintenance process: the power adapter uses switching power supply, and the input voltage range is 100 ~ 240V. If the voltage exceeds 240V, the power adapter may be burned out. Open the plastic shell of the power adapter and see that the fuse has blown, the varistor has burned out, and one of the pins has been burned out. Use a multimeter to measure whether the power circuit has obvious short circuit. Replace the fuse and varistor of the same specification, and connect the power adapter. The power adapter can still operate normally. In this way, the protection power supply circuit in the power adapter is relatively perfect.
From the actual circuit analysis, the varistor is connected in parallel with the input of the bridge rectifier diode. Its function is to use its “Self Fusing” in case of instantaneous high voltage intrusion, so as to protect other components of a part of the power adapter from high voltage damage.
Under the condition of normal 220V power supply voltage, if there is no varistor of similar specifications on hand, the resistor can not be installed for emergency use.
However, it should be installed immediately after purchasing the varistor. Otherwise, there will be endless trouble, ranging from burning out many components in the power adapter to burning out the notebook computer.
To repair the disassembled plastic shell of the power adapter, you can use polyurethane glue to repair it. If there is no polyurethane glue, you can also use black electrical tape to wrap several circles around the plastic shell of the power adapter.
2、 What if the power adapter squeaks
A power adapter makes a very loud “squeak” sound during operation, which interferes with the running mood of consumers.
Maintenance process: under normal circumstances, it is normal for the power adapter to have small operating noise, but if the noise is annoying, that is the problem. Because in the power adapter, only when there is a large movable gap between the switching transformer or the magnetic ring of the inductance coil and the coil, the “squeak” will be caused. After removing the power adapter, gently move a part of the coils on the two inductors by hand under the condition of no power supply. If there is no feeling of looseness, it is certain that the operation noise source of the power adapter comes from the switching transformer.
The methods to eliminate the “squeak” sound of switching transformer during operation are as follows:
(1) Use an electric soldering iron to re weld the connection solder joints between several pins of the switch transformer and the printed circuit board. During welding, press the switch transformer towards the circuit board by hand to make the bottom of the switch transformer in close contact with the circuit board.
(2) Insert a proper plastic plate between the magnetic core and coil of the switching transformer or seal it with polyurethane glue.
(3) Place hard paper or plastic plates between the switch transformer and the circuit board.
In this example, the first method has no effect, so the switching transformer can only be removed from the circuit board, and the “squeak” sound is eliminated by another method.
Therefore, when purchasing the power adapter, it is also necessary to control the quality of the produced power adapter transformer, which can at least save a lot of inconvenience!
Post time: Mar-22-2022
