How to use a multimeter to detect and repair a variety of faulty circuit boards
(1) Off-line detection
Measure the positive and negative resistance value between each pin of the ic chip on the ground target, so as to analyze and compare with the good ic chip technology, so that you can find a fault.how to test pcb board with a multimeter?
(2) Online detection
1) Detect DC resistance. The same as offline detection, but please note that.
A. Disconnect the power supply on the circuit board to be tested.
B. The internal voltage of the multimeter should not be greater than 6V.
C.When measuring, attention should be paid to peripheral influences, such as the potentiometer connected to the ic chip.
(2) DC system work for voltage measurement method. Measured DC output voltage of each leg of the ic chip compared to the normal value we can, but also at the same time should pay attention to.
A universal meter to have a large enough internal resistance, digital meter is preferred.
B. Turn all potentiometers to the center position.
C. Watch pens or probes should take anti-slip measures. A bicycle spool can be used to cover the pen tip, which should be about 5 meters long.
D.If the measured value is inconsistent with the normal value, the voltage of the pin should be used to determine whether it affects the normal value of the ic chip and to analyze the corresponding changes in the voltage of other pins.
E. When the periphery has a leakage, short circuit, open circuit or deterioration, etc., ic chip control pin output voltage will be affected by the peripheral electronic components.
F. IC chip parts pin abnormal, then from the deviation of the big hand. First check the peripheral components, such as no fault, the IC chip is damaged.
G. For work with dynamic signals on the board, with and without signal ic chip pin voltage is different. But if the change is not normal, the ic chip may be bad.
The IC pin voltages of different operating mode devices are different in different operating modes.
3) AC working voltage test method. Use a multimeter with a db block to measure the approximate AC voltage of the ic. If there is no db block, you can connect an isolated DC capacitor of 0.1~0.5uf in series with the positive contact pin. This method is suitable for ic with lower operating frequency, but it should be noted that these signals are different due to different inherent frequencies and waveforms, so the measured data is approximate and is for reference only.
(4) total current direct measurement method. By measuring the total current of the ic power supply, to identify the good and bad ic. As most of the internal control of the ic for the DC system coupling, ic damage (such as pn junction breakdown or open circuit) will cause saturation and cut-off of the back stage, so that the total current can be developed. So the total current can be measured to determine the good and bad ic, online analysis of a circuit measured on the resistance of the voltage, can be calculated according to the value of different currents.
The above detection methods have their own advantages and disadvantages,pcblink 1oz vs 2oz Copper in the practical application of these methods will be used in combination. Used well can repair a variety of circuit boards.
(3) Do not rely too much on the online tester.
1) Functional testing can not replace parametric testing.
2) Functional test can only test the device cut-off area, amplification area and saturation area, can not know the operating frequency and speed at this time of fast J diffusion.
3) For digital control chip companies, only know that there are high and low levels of output data changes, but can not find out in time the speed of development of its rising and falling edge changes.
4) For analog chips, it deals with analog changes. The distribution of receiving circuit components and the solution of different signaling schemes are complex. At present, it is impossible to solve the online testing problem of analog chips. Therefore, the results of this functional test are for reference only.
5) Most on-line testers will give a prompt of "pass test" or "test failed" after the functional test of various chips on the board. This is the disadvantage of this tester. Because there are too many factors affecting (interfering with) in-circuit testing. Requires a lot of measures to be taken before the test (such as disconnecting the crystal, removing the cpu and chip with the program, adding isolated interrupt signals, etc.). . It is worth investigating whether these measures are effective. At least, the current test results are sometimes unsatisfactory.
6) Anyone who knows anything about in-circuit testing knows the terms. Chips that do not pass in-circuit testing are not necessarily damaged; Chips that pass in-circuit testing are not necessarily damaged It is easy to understand why a chip that fails in-circuit testing may not pass if the device is compromised or resistant to interference. So, would a damaged chip in a test result in a "no"? The answer is not really certain. In some cases, the chip is damaged (or rather, the board does not work properly), but the test passes. The authoritative explanation is that this is the principle of the tester himself (after the driving technique). Therefore, we can not rely too much on the role of in-line testers.
