Power Adapter Troubleshooting Guide

The principle of the general adapter is shown in the figure, which is composed of voltage transformation, rectification, filtering, voltage stabilization and other parts. In case of failure, the following steps can be taken.

1. False load method

When repairing the AC power adapter, in order to distinguish whether the fault is in the load circuit or the power supply itself, it is often necessary to disconnect the main load and add a dummy load to the main voltage output end of the power adapter for test, as shown in Figure 4-1. The reason why the false load should be connected is that during the cut-off period, the energy stored in the primary winding of the switch transformer should be released to the secondary side. If the false load is not connected, the energy stored in the switch transformer will not be released anywhere, which will easily lead to the breakdown and damage of the switch tube. As for the false load, it should be selected according to the output voltage (or power) of the power adapter. Generally speaking, if the output voltage is more than 100V, 40-100w bulb or 300 Ω high-power resistor should be selected as the false load; if the output voltage is less than 30V, the bulb or 600 Ω-1k Ω high-power resistor used on the automobile / motorcycle can be selected as the false load.

Fig. false load access location

In addition, it should be noted that for some electronic products, the DC voltage output terminal of the power adapter is grounded through a resistance, which is equivalent to a dummy load. Therefore, for the power adapter of this structure, it is not necessary to connect the dummy load again during maintenance.

2. Short circuit method

The parallel desktop power adapter generally adopts the direct sampling voltage stabilizing control circuit with optocoupler. When the output voltage is high, the short circuit method can be used to distinguish the fault range.

The process of the short circuit maintenance method is: first short-circuit the two pins of the photosensitive receiving tube of the optocoupler, which is equivalent to reducing the internal resistance of the photosensitive receiving tube. If the measured main voltage remains unchanged, it means that the fault is behind the optocoupler (one side of the primary circuit of the switching transformer). Conversely, the fault is in the circuit before the optocoupler.

It should be noted that the short circuit method should be carried out on the basis of being familiar with the circuit, and blind short circuit is not allowed to avoid fault expansion. In addition, from the perspective of maintenance safety, the load circuit should be disconnected before short circuit.

3. Series bulb method

The so-called series bulb method is to take out the fuse (fuse) of the input circuit and use a 60W / 220V bulb to string at both ends of the fuse. When AC is connected, if the bulb is on, the circuit is short circuited. Because the bulb has a certain resistance value, such as 60W / 220V bulb, its resistance value is about 500 Ω (referring to thermal resistance), so it plays a certain role in current limiting. In this way, on the one hand, the circuit fault can be roughly judged by the brightness of the bulb; on the other hand, due to the current limiting effect of the bulb, the existing short circuit circuit circuit will not burn out the components immediately. After clearing the short circuit fault, the brightness of the bulb will naturally darken. Finally, remove the bulb and replace it with a fuse.

4. Substitution

Substitution can be divided into component level substitution and board level substitution.

Component level replacement refers to replacing suspected components with normal components. If the power adapter works normally after replacement, it means that the replaced components are damaged. In the power adapter, some components can be directly judged by multimeter, such as resistance; some are not easy to judge, such as power control chip. Therefore, for the components that are difficult to judge, if it is suspected that there is a problem in the maintenance, it is recommended to use the correct components for replacement to improve the maintenance efficiency.

Board level replacement refers to the overall replacement of the whole power adapter or a part of the power circuit. This maintenance method is mainly used for the maintenance of power adapter when large area components are burned out or power adapter has difficult faults. This maintenance method is characterized by complete troubleshooting, high maintenance efficiency, but relatively high cost. There are many ways to repair the power supply, such as oscilloscope method, heating and cooling method, manual intervention method, etc., which will not be introduced here.

The above are the four steps of power adapter maintenance. Through these four steps, we can check the power adapter well. Of course, if there is no big problem, it's better not to open the shell easily. If necessary, it's better to find a professional.

Company File:

Shenzhen Super Dragon Technology Co.,Ltd. was founded in March 2008 and is known for its efficient management team and an experienced R&D and process development team.

Power supply business is a division integrating R&D/production/sales/customer service. We mainly provide customer a few series of eco-friendly adapter, charger, smart fast charger, power converter module for telecom and so on. Our products have ac power adapter, wall mount power adapter, desktop power adapter and so on. We have a professional R&D team and talents are gathered in production, engineering, quality team too. Relay on the strong ability of development, manufacture and quality control , we can provide eco-friendly and price competitive products to consumer along with high quality.