Short circuit detection method and phenomenon analysis of IC chip

Date：2021-12-20 17:23:52Views：2146

Chips are actually the gathering place of integrated circuits. A chip consists of thousands of integrated lattices. However, the level and density of specific chip integration are determined by the function and function of the chip.

The phenomenon of IC chip damage also exists, but the premise is that the power supply to the chip is too high or the current is too large, which will lead to chip damage because the internal circuit of the chip exceeds its limit working current and voltage. Another way to damage the chip is the damage caused by instantaneous high current and high voltage due to the failure in the actual circuit of the chip. Another case is that the chip is damaged during power on due to defective workmanship. In addition, due to improper operation of the chip and failure to take anti-static measures, the chip is damaged by static electricity. There is static electricity everywhere in life, and static electricity is very harmful. If anti-static measures are not taken, it is difficult to find the cause of the damage of many chip devices.

For a frequency converter, the switching power supply has intermittent oscillation, and the operation display panel is also on and off. This is a typical fault of switching power supply with heavy load or short circuit. The abnormal load causes the protection action of switching power supply current detection circuit, making the switching power supply in intermittent oscillation state.

Use the method of disconnecting the load circuit one by one to find out which load circuit is the cause of the short-circuit fault, or after power failure, measure the output end of each power supply to see if there is resistance reduction or short circuit. Measure both ends of + 5V power supply, showing a small resistance value of 7.8 Ω, while the normal circuit resistance value is about hundreds of Ω. Judge that there is a short circuit in the + 5V load circuit. After disconnecting the + 5V load circuit, the switching power supply has a stable output, indicating that the fault is in the + 5V load circuit.

+The 5V power supply goes to the CPU main board from the wiring terminal to supply the CPU chip and peripheral circuits. The circuit range is relatively wide. There are more + 5V power supply integrated circuits on the CPU main board, up to more than 20 pieces. If the short-circuit fault is checked by the conventional troubleshooting method, the + 5V power supply pin of each IC circuit must be removed, and cooperate with the resistance value detection of the power output end. When a certain IC power supply pin is removed, After the small resistance value of 7.8 Ω at the power output becomes the normal resistance value, it indicates that there is a short circuit fault in the IC. Of course, it is the same to measure the resistance value of the power supply pin by picking out the power supply pin of the IC.

It is impossible to predict how many ICs need to be removed before finding the faulty IC. The "fineness" of CPU motherboard component welding has been difficult to connect to the circuit board of mobile phone. IC circuits are all chip components, and the copper foil strip of IC pin is very thin.

Due to the limited load capacity of the switching power supply of the frequency converter, it will cause overcurrent protection when connected to the fault circuit, so that the switching power supply stops output. Therefore, an external + 5V power supply with large capacity is adopted, and a 5 Ω 5W current limiting resistor is connected in series to the CPU motherboard. After a few minutes of power on, touch the IC chip on the CPU motherboard by hand. Which chip is hot and has abnormal temperature rise, that is, which IC has broken down. Pick out two IC power supply pins with abnormal temperature rise, and measure the pin resistance, which is about ten Ω. At this time, measure the + 5V power output, which is already a normal resistance value of hundreds of Ω.

This method uses external + 5V power supply, which not only does no harm to the good IC, but also causes the bad IC to continue to heat up and be exposed to the "thermometer" of the finger. It is especially suitable for detecting ic short circuit fault on CPU motherboard. Generally, in case of short-circuit fault of circuit board, there is no good maintenance idea through circuit analysis. Directly connect appropriate external power supply to the short-circuit circuit part, touch or check the heating IC with thermal imaging, so as to quickly find the short-circuit components. This method can often provide great help in repairing the short-circuit fault circuit board.