PCB News - How to detect the VCC short circuit in the circuit board?

How to detect the VCC short circuit in the circuit board?

At this stage, the indispensability of electrical appliances makes PCBA boards in electrical appliances in short supply. In PCBA processing plants, there are dedicated quality inspection and maintenance personnel. Their task is to detect defects and failures of the circuit boards produced by the circuit board manufacturers, and perform maintenance.

In circuit board maintenance, it is a headache if you encounter a short circuit of the VCC power supply, because there are too many components connected in parallel between VCC and GND, including chips, capacitors, and transistors. It may be short-circuited, and the tin point and copper foil may also be short-circuited. General maintenance personnel will remove the components one by one until the short circuit is eliminated after removing a certain component. If you are unlucky, the components on the entire board are almost removed and the fault is not found. Not only can the fault not be found, but also It will damage the circuit board. Here are some more convenient methods for everyone.

In circuit board maintenance, it is a headache if you encounter a short circuit of the VCC power supply, because there are too many components connected in parallel between VCC and GND, including chips, capacitors, and transistors. It may be short-circuited, and the tin point and copper foil may also be short-circuited. General maintenance personnel will remove the components one by one until the short circuit is eliminated after removing a certain component. If you are unlucky, the components on the entire board are almost removed and the fault is not found. Not only can the fault not be found, but also It will damage the circuit board.

Here are some more convenient methods for everyone:

For the plug-in capacitor on the circuit board, you can use diagonal pliers to cut off one foot (be careful to cut from the middle, do not cut all the roots or cut the circuit board). The plug-in IC can cut off the power VCC pin, and the short circuit disappears when one of the legs is cut. Then a chip or capacitor is short-circuited. If it is a SMD IC, you can use an electric soldering iron to melt the solder on the power pin of the IC and lift it up to leave the VCC power supply. After replacing the short-circuit components, re-weld the cut or upturned parts. If it is a patch capacitor connected to both ends of the power supply VCC, you can blow them off one by one with a hot-air soldering station. If you remove one, use a multimeter to measure it until it is not short-circuited.

There is also a quicker method, but a special meter-a milliohm meter is used. We know that the copper foil on the circuit board also has resistance. If the thickness of the copper foil on the PCB is 35um and the printed line width is 1mm, then every 10mm length, its resistance value is about 5mΩ, such a small resistance value, use ordinary The multimeter cannot be measured, but it can be measured with a milliohm meter. We assume that a certain component is short-circuited. It is 0Ω measured with an ordinary multimeter, and it may be tens of milliohms to hundreds of milliohms when measured with a milliohm meter. The resistance value must be the smallest (because if it is measured on the two pins of other components, the resistance value obtained also includes the resistance value of the copper foil trace on the circuit board), so we compare the resistance difference of the milliohm meter, when When the resistance value obtained by measuring a certain component (if it is solder or copper foil has a short circuit) is the smallest, then the component is the key suspect. In this way, the point of failure can be quickly found.