How to measure chip quality

1. Check power supply: directly measure the VCC and GND levels with a multimeter, and see if they meet the requirements.If the VCC deviates too much from 5V or 3.3v, check the output of 7805 or other voltage stabilizing and filtering circuits.

2. Check crystal vibration......I do not know how to check the crystal oscillator, my method is relatively soil: generally is to change a few crystal oscillator to try on the power, anyway quartz crystal oscillator is not worth a lot of money:)

3. Check the level logic of RESET pin, and note whether the model used is RESET at high level or low level. If the MCU has been RESET repeatedly, the result is self-evident.

4. If the program starts from the external ROM of the extension at design time, check the EA footer.

5. Check whether the MCU is damaged or the flash cannot be downloaded. It is better to try a new chip.

6. If all the above points are confirmed to be correct, the hardware should run normally according to the theory (in order to prevent an accident, you can also write a shorter program to test the minimum system)......If the test program works correctly.Then it is basically determined to be the problem of the control program. Keep track of the debugging program repeatedly in keil, and pay attention to whether the working register group, accumulator, DPTR and other values after calling the subroutine are the expected values.

How to judge the stand or fall of IC chip

One, not road detection

This method is carried out when IC is not welded into the circuit. In general, a multimeter can be used to measure the positive and negative resistance values of each pin corresponding to the grounding pin and compare them with intact IC.

Two, in the road detection

This is a multimeter test method for detecting the dc resistance of each IC pin in the circuit (IC in the circuit), the dc voltage to the ground and the total working current.This method overcomes the limitation of substitutable IC test method and the trouble of disassembling IC, and is the most common and practical method to detect IC.

2.Dc working voltage measurement

This is a kind of dc supply voltage and the working voltage of peripheral components are measured with the multimeter dc voltage block under the condition of power on.Test the dc voltage of each IC pin to the ground and compare it with the normal value, so as to compress the fault range and find out the damaged components.Please note the following eight points when making measurements:

(1) the multimeter should have enough internal resistance, less than 10 times of the circuit resistance under test, so as to avoid large measurement errors.

(2) usually the potentiometer to the middle position, if it is a television, signal source to use standard color signal generator.

3) watch pen or probe to take anti-slip measures.Any instantaneous short circuit is easy to damage IC.The following method can be adopted to prevent the watch pen from sliding: take a section of the bicycle valve cover on the table nib, and grow out of the table nib about 0.About 5mm, this can make the table nib good contact with the test point, and can effectively prevent slipping, even if hit adjacent points will not short circuit.

(4) when the measured pin voltage is inconsistent with the normal value, it should be analyzed according to whether the pin voltage has an important impact on the normal operation of IC and the corresponding changes of other pin voltages to judge the quality of IC.

(5) IC pin voltage will be affected by peripheral components.When the external components have leakage, short circuit, open circuit or variable value, or the peripheral circuit is connected to a resistance variable potentiometer, then the position of the potentiometer sliding arm is different, will make the pin voltage change.

(6) if the voltage of each IC pin is normal, it is generally considered that IC is normal;If the IC part of the pin voltage is abnormal, then from the largest deviation from the normal value, check the peripheral components have no fault, if no fault, IC is likely to damage.

(7) for dynamic receiver devices, such as TV set, when there is no signal, IC pin voltage is different.If it is found that the pin voltage should not change but changes greatly, which changes with the signal size and different positions of adjustable components but does not change, IC damage can be determined.

(8) for devices with multiple working modes, such as video recorder, under different working modes, the voltage of each IC pin is also different.

3.Ac working voltage measurement method

In order to grasp the change of IC ac signal, a multimeter with db jack can be used for approximate measurement of IC ac working voltage.When testing, the multimeter is placed in ac voltage block, and the watch pen is inserted into the db jack;For multimeters without db jack, a 0 needs to be concatenated in the positive meter pen.1 to 0.5 f spacer capacitors.This method is applicable to IC with lower working frequency, such as video amplification level of TV set, field scanning circuit, etc.Since the natural frequencies and waveforms of these circuits are different, the measured data are approximate and can only be used for reference.

4.Total current measurement

This method is a method to judge the quality of IC by detecting the total current of the incoming line of IC power supply.As most of the internal IC is directly coupled, when the IC is damaged (such as a breakdown of a pn junction or open circuit), it will cause the saturation and cutoff of the later stage and make the total current change.So the method that measures total current can judge IC stand or fall.It is also possible to measure the voltage drop of the resistance in the power supply path and calculate the total current value with ohm's law.