How to quickly find GND in PCB?
1 Find GND through electrolytic capacitor
The picture above shows an induction cooker mainboard. To find the ground wire, we must first find the largest electrolytic capacitor on the board.
Generally speaking, relatively large electrolytic capacitors are used as a component for power supply filtering, and their negative electrode is GND.
The largest electrolytic capacitor you see in the picture above is a power supply filter capacitor. It rectifies and outputs a pulsating DC power of about 300 volts from the rectifier bridge. It is then filtered by this capacitor to output a relatively smooth DC power. Its negative pole is the negative pole of the DC power supply, which is the GND ground wire we are looking for.
2 Confirm GND by looking at the large piece of copper foil
The picture above is a two-layer board. The points marked with red circles in the picture are the ground wires. It can be seen that it is connected to a large piece of copper foil. This is because the ground wire has a shielding effect, which can effectively reduce the interference caused by the ground wire loop, so the ground wire copper foil in the circuit board generally appears in pieces.
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3 Confirm GND by looking at the logo on the connecting plug
As shown in the picture above, there are usually various signal marks on the connectors of the board. We can confirm the ground wire by looking at this mark. For example, the GND in the red coil in the picture above is the ground wire.
4 Search through integrated chip
There are usually various integrated circuits in the circuit board. If these integrated circuits want to work properly, they need a power supply. You can confirm the GND by looking at the pins of the chip.
As shown in the picture above, this is an 8-pin LM358 comparator. By searching its information, you can see the function of each pin. As long as you know that the fourth pin is GND, you can find the ground wire on the board.