PCB News - Analysis of common failures of circuit boards

Analysis of common failures of circuit boards

Editor of PCB electronics factory: Various electrical faults from time to time may include the following situations:

1. Poor contact: poor contact between the circuit board card and the slot, when the cable is broken internally, the connection is blocked, the wire plug and the terminal are not in contact, and the components are soldered.

The solution to this type of failure is to carefully check the suspected connector to see if there is any obvious oxidation or poor contact, scrape the oxidized metal contact point, adjust the position of the contact point, and redial after processing to test whether the contact is good .

2. The signal is disturbed: For digital circuits, the malfunction will only appear when I am drunk and sleepy under certain circumstances. It is possible that too much interference has affected the control system and caused errors, and there are also changes in individual component parameters or overall performance parameters of the circuit board, which makes the anti-interference ability approach a critical point, resulting in failure.

This type of fault focuses on checking whether the equipment is well grounded. Use a test pencil to check whether the equipment shell is live, or use a meter to measure whether the equipment shell has a high voltage to the ground, generally below 1V. If it is above 10V, you must suspect whether the grounding is good. .

3. Moisture and dust on the circuit board: Moisture and dust will conduct electricity and have a resistance effect, and the resistance value will change during the process of thermal expansion and contraction. This resistance value will have related effects with other components, When the effect is relatively strong, the circuit parameters will be changed, causing the failure to occur. This type of failure can be resolved by cleaning the circuit board. It is recommended to use board washing water to clean the circuit board, or directly use clean water to clean it, and then use a hair dryer to dry it thoroughly. It is not recommended to use alcohol, because it is easy to leave some white substances on the board after alcohol cleaning.

Fourth, the thermal stability of components is not good: From a large number of maintenance practices, the thermal stability of electrolytic capacitors is the first to be poor, followed by other capacitors, transistors, diodes, ICs, resistors, etc.

1. Thermal stability faults are soft faults. It is not easy to directly detect and determine the faulty components during maintenance. However, the inspection range can be narrowed by artificially heating or cooling the suspected components. You can use a hair dryer or an electric heat gun to heat the suspected component, and use a cotton swab dipped in alcohol to cool the suspected component. And the quality of the capacitor is easy to distinguish by using the VI curve test.

2. This kind of failure will generally appear or disappear with the lapse of the machine's start-up time. The essence is that the failure changes with the temperature change of a malfunctioning component. For example, the faults caused by the aging of electrolytic capacitors usually appear as soon as the power is turned on, and the faults disappear after a period of time when the power is turned on, that is, there is a fault when the machine is cold, but there is no fault when the machine is warm. The essence is: the capacitance of the aging electrolytic capacitor changes with the temperature. When the temperature is low, the capacity is small, resulting in poor filtering and the circuit board cannot work normally. With the power-on time, the temperature of the electrolytic capacitor rises and the capacity increases., The filter condition is satisfied, and the fault disappears again.

5. Software is also one of the considerations: Many parameters in the circuit are adjusted by software. The margin of some parameters is adjusted too low and is in the critical range. When the operating conditions of the machine meet the reason for the software to determine the fault, the alarm will change. Appear.

This type of fault can be resolved by adjusting the relevant parameters. For example, if the acceleration and deceleration time of the inverter is set improperly, an overcurrent and overload alarm may occur during operation; if the CNC processing parameters are set improperly, the processed product may not meet the requirements. In these situations, the parameters should be suspected at the first time Set up problems, and after eliminating the possibility of improper parameter settings, do you suspect the problem of the device itself.

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