PCB Tech - How to find the ground wire on the circuit board

When analyzing or repairing a PCB circuit board, it is often necessary to find out the ground wire (ie GND) of the circuit board. Generally, we can find out the positive and negative pins of the power supply filter capacitor, integrated circuit, Zener diode and other components on the circuit board. Quickly find the ground wire on the circuit board.

1. Find the ground wire according to the power supply filter capacitor

When looking for the ground wire on the circuit board, we can generally find the ground wire according to the power filter capacitor on the circuit board.

2. Find the ground wire according to the positive and negative power terminals of the integrated circuit

In addition to finding the ground wire according to the power filter capacitor, we can also find the ground wire according to the positive and negative pins of many integrated circuits on the circuit board.

For the 78XX series three-terminal stabilized integrated circuits, the 2. pin is the GND terminal. Generally, this pin is grounded in the circuit, so the copper foil connected to the 78XX pin 2. on the circuit board is the ground wire.

For 74LS00 series and CD4000 series digital ICs, the positive and negative power supply pins are fixed. If the digital IC is 14-pin and 16-pin, its 7-pin or 8-pin is the negative terminal of the power supply (grounded in the circuit), 14 Pin or pin 16 is the positive terminal of the power supply, so the ground wire on the circuit board can be quickly found from the power supply pin of the above-mentioned digital IC.

How to quickly find the ground wire on the PCB circuit board

3. Find the ground wire according to the pins of the voltage regulator tube and the transistor

If the voltage regulator tube is used as a voltage regulator in the circuit, its positive electrode is generally grounded. If the NPN transistor is used as an electronic switch, its emitter is mostly grounded, so it can be quickly found based on the pins of the above components The ground wire on the circuit board.

4. First look at whether there is a large area of copper on the circuit board. If there is copper, then observe whether the pad of the component is connected to this piece of copper. If there is, then it can basically be determined that this piece of copper is GND, because Most of the copper-clad designs of low-frequency circuits are designed as GND;

5. Find some common components on the circuit board, such as polarized capacitors, voltage regulator modules, or sockets with metal shells (such as network cable sockets), and look at several capacitors to see if there are many negative poles connected to the same line On the upper; Wenya module check the pin to find the GND pin wiring; the metal shell connector is generally GND if the shell is welded to the board

6. Check what kind of interface the power supply interface of the circuit board is. The definition can be found on mainstream sockets such as circular socket USB and so on. The GND corresponding to the circuit board found in the definition is generally the circuit board GND.

7. There are also some circuit designs that connect the metal part of the product shell to the circuit board through wires or screws, so the wiring or screw holes are likely to be GND.