Usually, there are many circuit boards in a device that need to be maintained. When you get a device to repair a faulty circuit board, you should first judge the approximate location of the fault according to the fault phenomenon, then gradually narrow the possible location of the fault through measurement, and finally find the fault. The following describes the specific circuit board maintenance testing methods, welcome to read.
First, the commonly used maintenance detection methods
Common circuit board maintenance detection methods include on-line measurement, off-line measurement and substitution method.
1. Offline measurement refers to offline measurement. When the circuit board is not welded into the circuit during maintenance, the DC resistance between pins is measured and compared with that between pins of a known normal circuit board of the same model to determine whether it is normal.
2. Online measurement refers to online measurement, which uses voltage measurement, resistance measurement and current measurement to judge whether the circuit board maintenance is damaged by measuring whether the voltage value, resistance value and current value of each pin of the circuit board maintenance are normal.
3. The replacement method refers to replacing the tested circuit board with a known intact circuit board of the same model and specification, which can judge whether the circuit board maintenance is damaged.
4. The separation test method, also known as the circuit segmentation method, is a fault inspection method that reasonably separates the circuits related to the fault in electronic equipment according to the components in order to clarify the circuit range where the fault is located. This method is to confirm some circuits and deny some circuits through several separate inspections, and gradually narrow the circuit range where the fault may occur until the fault location is found.
5. Signal injection method: This method uses different output signals of external signal sources as known test signals, and uses the terminal indicator of the tested electronic equipment to indicate the test results. When checking, according to the specific requirements, select the corresponding signal source to get the known signals with different indexes; Check from the back stage to the front stage, that is, inject the known signal from the input end of the terminal indicator of the device under test, and then sequentially from the back stage circuit to the front stage circuit. In the maintenance of industrial circuit boards in Xinjiang, known and different test signals are injected into the input terminals of all levels of circuits, and whether the indicator light on the terminal surface of the tested equipment reacts normally is observed, so as to determine the fault location and analyze the fault causes.
6. Intuition inspection method: This method refers to relying on people's intuition, not using any instruments and equipment, and not welding any circuit components? The method of checking the fault of the circuit board to be repaired by vision, smell, hearing and touch. Intuition check is the simplest method of equipment failure. This method can be divided into live inspection method and non-live inspection method.
7. Signal tracking method: This method uses a single test signal and uses test instruments (such as oscilloscope and electronic voltmeter) to check (track) step by step from front to back. This method can deeply and quantitatively check all levels of circuits and quickly determine the fault location.
8. AC short circuit method: also known as capacitor bypass method, it is a method of bypassing a part of the circuit of the electronic equipment under test with a capacitor with appropriate capacity and withstand voltage. This is a relatively simple and fast fault checking method. Ac short circuit method is suitable for judging the circuit part of electronic equipment that produces power interference and parasitic oscillation.
9. Parameter test method: It is a method of electronic equipment fault inspection by using instruments (such as Huineng ic online maintenance tester) to test the voltage value, current value, component value and component parameters in the electronic equipment circuit. Usually, the resistance value is not measured by electricity; Measure the voltage value and current value in the energized state; Or remove components and measure their related parameters.
10. waveform observation method: this is a dynamic test method for electronic equipment. With the aid of oscilloscope, observe the waveform of the fault part or related part of electronic equipment; According to the difference between the waveform shape, amplitude parameters and time parameters obtained from the test and the normal waveform parameters of electronic equipment, the fault causes are analyzed and maintenance measures are taken. In the maintenance of industrial control circuit board, waveform observation is a very important quantitative test and maintenance method.
Second, the detection of common circuit board maintenance
1. Maintenance and inspection of microprocessor circuit board. The key test pins for microprocessor circuit board maintenance include power supply terminal, RESET terminal, XIN crystal oscillator signal input terminal, XOUT crystal oscillator signal output terminal and other input and output terminals. Measure the resistance and voltage values of these key feet to the ground on the road surface to see if they are the same as the normal values (which can be found in the product circuit diagram or related maintenance materials). The reset voltages of different types of microprocessors are also different, and some are low-level reset, that is, low-level at the moment of startup and high-level after reset; Have a plenty of high-level reset, that is, high level at the moment of switching and low level after reset.
2. Maintenance and inspection of switching power supply circuit board. The key pin voltages of switching power supply circuit board maintenance include power supply terminal (VCC), excitation pulse output terminal, voltage detection input terminal and current detection input terminal. Measure. Voltage value and resistance value of each pin to ground. If there is a big difference from the normal value, it can be determined that the circuit board is damaged under the condition that its peripheral components are normal. The maintenance of thick film circuit board with built-in high-power switch tube can also judge whether the switch tube is normal by measuring the positive and negative resistance values between the C, B and E poles of the switch tube.
3. Audio power amplifier circuit board maintenance inspection. When checking and repairing the circuit board of audio power amplifier, the voltage and resistance value of its power terminal (positive power terminal and negative power terminal), audio input terminal, audio output terminal and feedback terminal to ground should be detected first. If the measured data value of each pin is quite different from the normal value, and its peripheral components are normal, it is the internal damage of circuit board maintenance. Signal interference method can be used to check the maintenance of audio power amplifier circuit board which causes silent fault when the power supply voltage is normal. When measuring, the multimeter should be placed in R? In the 1 position, ground the red stylus and touch the audio input with the black stylus. Under normal circumstances, there should be a strong? Kaka? Sound.
4. Maintenance and inspection of servo amplifier circuit board. Measure the voltage between the output terminal of the operational amplifier and the negative terminal of the power supply with a multimeter (the voltage value is higher at static state). Touch the two input terminals of the operational amplifier in turn with hand-held metal tweezers (add interference signal). If the pointer of the multimeter swings greatly, the operational amplifier is in good condition. If the multimeter pointer does not move, the operational amplifier is damaged.
5. Detection of time base circuit board maintenance. The maintenance of time-base circuit board includes digital circuit and analog circuit, so it is difficult to measure its quality directly with multimeter. The test circuit shown can be used to test the maintenance quality of time base circuit board. The test circuit consists of resistance-capacitance element, light-emitting diode LED, 6V DC power supply, power switch S and 8-pin IC socket. After inserting the time-base circuit board maintenance (such as NE555) into the IC socket, press the power switch S. If the time-base circuit board under test is in normal maintenance state, the LED will flash. If the LED is always off or on, it means that the maintenance performance of the tested time base circuit board is poor.
6. Maintenance separation detection of industrial control circuit board: a fault detection method that reasonably separates the industrial control circuit board from the circuit related to the fault, so as to clarify the circuit range where the fault is located. In this way, through repeated separation inspection, some circuits are affirmed and some circuits are denied, thus gradually narrowing the range of circuits that may fail until the fault position is found.