Crystal oscillator quality measurement tips
Release date: 2017-10-26 Source: Foreign station sharing: 
Crystal oscillator quality measurement tips
The measurement of the quality of the crystal oscillator often makes the beginner scratch his head. The crystal oscillator is relatively small, but the role played on the motherboard is not small, so the detection of the crystal oscillator is a very important part of the motherboard maintenance. How to judge the quality of the detection crystal?
1. Use a multimeter (R × 10k block) to measure the resistance value at both ends of the crystal oscillator. If it is infinite, it means that the crystal oscillator has no short circuit or leakage; then insert the test pencil into the mains socket and pinch any pin of the crystal with your finger. Touch the other pin to the metal part at the top of the test pencil. If the test pencil is red, the crystal is good. If the bubble is not bright, the crystal is damaged.
2. Use a digital capacitance meter (or a digital multimeter's capacitance file) to measure its capacitance. Generally, the damaged crystal oscillator capacity is significantly reduced (different crystal oscillators have a certain range of normal capacity, which can be measured well, generally in tens to several Hundred PF
3. Close to the ear and gently shake, the sound must be bad (the internal crystal has been broken, and the frequency can also be changed if used)
4. Test the output pin voltage. Under normal circumstances, it is about half of the power supply voltage. Because the output is a sine wave (peak to peak close to the source voltage), when testing with a multimeter, it is almost half.
5. Measure with a substitution method or an oscilloscope.
Crystal and crystal detection methods and techniques
How to use a multimeter to measure whether the crystal oscillator starts to oscillate?
You can use a multimeter to measure whether the voltage of the two pins of the crystal oscillator is half of the working voltage of the chip. For example, if the working voltage is 5V, it is measured whether it is about 2.5V. In addition, if you touch the other foot of the crystal with a tweezers, this voltage has a significant change, which proves to be oscillating.
Tip: Just get a 1.5V battery and connect the crystal oscillator to the ear at the two ends of the crystal. Listen carefully. When you hear the humming sound, it means that it starts to vibrate. It is good!
Crystal detection method
Electric resistance method
Put the multimeter in the R×10K block and measure the resistance between the two pins of the quartz crystal to be infinite. If the measured resistance value is not infinite or even close to zero, it indicates that the crystal under test is leaking or breakdown.
This method can only measure whether the crystal is leaking. If there is an open circuit inside the crystal, the resistance method can't do anything. In this case, the method described below must be used.
2. Homemade tester
By soldering a simple quartz crystal tester, you can accurately test the quality of the crystal. The two test sockets can be removed from the socket in the small seven-legged or small nine-legged tube socket. It is better to select high brightness of the LED tube.
When detecting the quartz crystal, insert the two pins of the quartz crystal into the two sockets of XS1 and XS2, press the switch SB, if the quartz crystal is good, the oscillating circuit composed of the components such as the triode VT1, C1, C2, etc. Oscillation, the oscillating signal is coupled to the VD2 detection via C3, and the detected DC signal voltage turns VT2 on, so the LED connected in the VT2 collector circuit emits light, indicating that the quartz crystal to be tested is good, if the LED is not bright, then The quartz crystal being tested is bad. This tester tests quartz crystals at a wide frequency, but the optimum operating frequency is several hundred kilohertz to tens of megahertz.
Tag: Quality Measurement of Crystal Oscillator Tips
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