Repairing my laptop power adapter, I have a unique skill

"China computer education" this phase 38-39 "exchange of experience" column to introduce the principle, the notebook computer power adapter, we introduce several notebook computer power adapter maintenance examples, we hope to help. ?
Fault power adapter is common without low-voltage DC output, the output voltage is not stable or large deviation and inside a loud creak noise, which no voltage output is most common. ?
Example 1: a IBM laptop in use, because the 380V power line fell on the 220V civilian lighting line, resulting in power adapter burned, no voltage output. ?
Maintenance process: the input voltage range of the IBM power adapter for 100V~240V, a voltage exceeding 240V will likely burn the adapter. When the adapter shell is opened, it is found that the fuse has blown, and that the varistor R1 (Figure 1 is the schematic of the adapter) has been burned, and one of the pins has been blown off. Remove the varistor, change the fuse with the same specifications, use multimeter to measure the circuit without obvious short-circuit phenomenon, connect the adapter to the power supply, want to do general inspection, unexpectedly found the adapter has been working properly. It seems that the protection circuit in the IBM power adapter is quite perfect. If you do not have the same specifications of the varistor, can not install, but it only for emergency use, etc. to buy the varistor in time after installation, because once again suffered such pressure into the event, it could not protect their function, then the circuit elements may be a large number of burn.Maintenance process: multimeter is used to measure the output of power adapter, and no voltage output is found. After removing the Toshiba Laptop AC Adapter, it is found that the circuit boards near the high power rectifier bridge have burnt marks. The adapter is connected to the power supply in accordance with the maintenance procedures of the switching power supply, first use the multimeter to measure the input voltage for normal AC 220V; second A pacing (i.e. switching power tube Q1 C, Figure 7) of the measured voltage, 0V, measured B (filter capacitor C1 is extreme for the 0V (normal) voltage if there should be a DC voltage of about 310V), that the rectifying circuit fault; then measured C, D 2The voltage between the two ends of the varistor (R1) should be AC 220V and the voltage is 0V. Check that the fuse F1 (Figure 3) is found to have been blown. A fuse that indicates that the circuit is overloaded or has a short-circuit point. The printed circuit board, switch power tube C pole and switch transformer between the copper foil with a knife cut off (ie open at A), a new 2.5A fuse, the power adapter AC plug, just listen to "bang", and this shows that the fuse fuse, switch before in short circuit point. Then cut the filter capacitor C1, the positive electrode and the rectifier bridge output end of the copper foil (that is, at B points off), replaced with a new fuse after being blown again, indicating that the failure point before B. Because before the B point, only the rectifier bridge and fuse string loop, so suspect rectifier bridge was broken, remove the measurement found that model D3SB rectifier bridge (Figure 4) is indeed damaged. When replacing the rectifier bridge, it is found that the short circuit board below the filter capacitor C1 has traces of liquid drying, and the filter capacitor is removed. The capacitor has been seriously leaking, and the top of it has been bulging out (Figure 5). Replace the filter capacitor of the same specification, replace the fuse again, connect the adapter to the power supply, and measure the output of the adapter to have the normal 16V DC voltage output.

For safety reasons, it is better to use a dummy load to check the working stability of the Asus Laptop AC Adapters before it is put into service. The method is: to find a wire or electric resistance for the high-power 4 resistor connected to the output end of the adapter, the adapter to near full load working 1~2 hours, and the multimeter is used to monitor the output voltage (Figure 6), if the output voltage is always stable between 15.2~16.8V (16V + 5%), can be considered an adapter work stable, can be connected with the notebook computer for official use. ?
Example 3: when a power adapter is working, it sends out a big "squeak" sound. The distance from the adapter is also clear and audible, which seriously affects the working mood of the users. ?
Maintenance process: in general, there are weak noise power adapter is normal, but if the noise to the ring upsetting, it should be regarded as fault. However, this kind of fault source is easier to find, because there is only a switch transformer in the power adapter, and there is a large gap between the magnetic coil and the coil of the inductance coil, which will lead to "creak". After the adapter is dissected, the coil portion of the two inductance coils is gently struck by hand without the power supply. It is certain that the working noise of the HP Laptop AC Adapter comes from the switch transformer. ?
Eliminate the switch when the transformer works "squeak" sound methods:
With electric iron solder connection of switch transformer pins and printed circuit board welding, when welding by hand.

The transformer is pressed toward the circuit board, so that the bottom of the switch transformer is in close contact with the circuit board. ?
Plastic sheet in between the core switch transformer and the coil into the appropriate or sealed with epoxy resin. Between the switch transformer and the circuit board into the hard pad of paper or plastic film. ?
In this case, the method did not receive the results, and with the method of trying to succeed, squeak" sound is eliminated. Because the components on the printed circuit board are very dense, there are some difficulties in adopting the method II and the operation of the method. We can remove the switch transformer from the circuit board before proceeding.