How to detect faulty chips?

 How to detect faulty chips?

1. Check board method:

1) Observation method: burnt, broken board, blistering, broken board surface, corrosion of socket.

2) Meter test method: Check the resistance value of the chip with a Fluke 15+ multimeter, and compare it with the normal chip. There is no result that the resistance value is too different, indicating that the chip is faulty.

3) Power-on inspection: For broken board, you can slightly increase the voltage by 0.5-1V and rub the IC on the board after power-on to make the chip in question heat up and check it out through perception.

4) Identify the major working areas: most boards have a clear division of labor on the area, such as control area (CPU), clock area (crystal oscillator) (frequency division), etc.

2. Troubleshooting method:

1) First, use an oscilloscope to check whether there is a signal (waveform) at the input and output of the suspected faulty chip. Check the IC control signal (clock) if there is input or output. If there is, the IC is very likely to be broken. If there is no control signal, trace its previous chip until the damaged IC is found.

2) For the time being, don’t remove it from the pole and use the same model. Or put the IC with the same program content on it, turn it on, and observe whether it is getting better, to confirm whether the IC is damaged.

3) Use wire cutting and jumper methods to find short-circuit wires: some signal and ground wires are found. +5V or other pins that should not be connected to multiple ICs are short-circuited, you can cut off the line and measure again to determine whether it is an IC problem or a board wiring problem, or borrow a signal from another IC and solder it to an IC with the wrong waveform to see if the phenomenon is displayed. If it becomes better, judge the quality of the IC.

4) Comparison method: Find an exemplary circuit board with the same content to compare and measure the pin waveform and the number of the corresponding IC to confirm whether the IC is damaged.

5) Use the test fixture software to test and locate the chip fault location.

Precautions for IC chip testing

1. Understand the working principle of integrated circuits and related circuits before testing

Before inspecting and repairing the integrated circuit, you must first be familiar with the function of the integrated circuit used, the internal circuit, the main electrical parameters, the role of each pin, and the normal voltage of the pin, the waveform and the working principle of the circuit composed of peripheral components. If the above conditions are met, analysis and inspection will be much easier.

2. Do not cause a short circuit between the pins during the test

When measuring voltage or testing the waveform with an oscilloscope probe, do not cause a short circuit between the pins of the integrated circuit due to sliding of the test leads or probes. It is best to measure directly connected to the pins on the peripheral printed circuit. Any momentary short circuit can easily damage the integrated circuit. Therefore, you must be more careful when testing flat-package integrated circuits.

3. Using grounded test equipment to touch the live equipment on the backplane is strictly forbidden without an isolation transformer.

4. Pay attention to the insulation performance of the electric soldering iron

It is not allowed to use an electric soldering iron for soldering with electricity. It is best to ground the shell of the soldering iron. Also, be more careful with the MOS circuit. It is safer to use a low voltage circuit iron of 6~8V.

5. To ensure the welding quality

It is sure to be welded firmly when soldering, and the accumulation of solder and pores is likely to cause false soldering. The welding time generally does not exceed 3 seconds. Therefore, the integrated circuit that has been soldered should be carefully checked. It is best to use a Fluke 15b+ multimeter to measure whether there is a short circuit between the pins, confirm no solder adhesion phenomenon, and turn on the power.

6. Don't easily judge the damage of the integrated circuit

Do not easily judge that the integrated circuit is damaged easily. Because most of the integrated circuits are directly coupled, once a circuit is abnormal, it may cause multiple voltage changes, and the damage of the integrated circuit may not cause these changes. In addition, in some cases, the measured voltage of each pin is different from the normal voltage. When the values match or are close, it may not always mean that the integrated circuit is good because some soft faults will not cause changes in DC voltage.

7. The internal resistance of the test instrument should be large

When measuring the DC voltage of the IC pins, a multimeter with the internal resistance of the meter head more excellent than 20KΩ/V should be used. Otherwise, there will be a significant measurement error for the voltage of some pins.

8. Pay attention to the heat dissipation of power integrated circuits

The power integrated circuit should have a good heat sink, and it is not allowed to work in a high-power state without a heat sink.

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