Release date: 2017-10-26 Source: Foreign station Sharing:

Crystal oscillator quality measurement tips

Testing the quality of a crystal oscillator can be confusing for beginners. Although small in size, the crystal oscillator plays a crucial role on the motherboard, making its testing an essential part of motherboard maintenance. How can you determine if a crystal oscillator is working properly?

1. Use a multimeter (set to R × 10k) to measure the resistance between the two ends of the crystal oscillator. If it reads infinity, there is no short or leakage. Then, insert the test leads into a power socket and touch one pin of the crystal with your finger while touching the other pin to the metal part of the test lead. If the test lead lights up, the crystal is good. If it doesn’t light up, the crystal may be damaged.

2. Use a digital capacitance meter (or a digital multimeter’s capacitance setting) to measure the capacitance. A damaged crystal oscillator will typically show a significant drop in capacitance. The normal range varies depending on the type of crystal, usually ranging from tens to hundreds of picofarads.

3. Bring the crystal close to your ear and gently shake it. If you hear a crackling sound, it means the internal crystal has broken. Even if it still works, the frequency might be affected.

4. Measure the voltage at the output pin. Normally, it should be approximately half of the supply voltage. This is because the output is a sine wave, and when measured with a multimeter, it reads close to half the peak-to-peak voltage.

5. Test using a substitution method or an oscilloscope for more accurate results.

How to use a multimeter to check if a crystal oscillator is oscillating?

You can use a multimeter to check if the voltage across the two pins of the crystal oscillator is about half the chip's operating voltage. For example, if the operating voltage is 5V, the reading should be around 2.5V. Additionally, if you touch one end of the crystal with a pair of tweezers, the voltage should change significantly, indicating that the crystal is oscillating.

Tip: Connect the crystal to a 1.5V battery and place it near your ear. If you hear a humming sound, it means the crystal is vibrating and functioning properly.

Crystal Detection Method

Resistance Method

Set the multimeter to R×10K and measure the resistance between the two pins of the quartz crystal. It should read infinity. If the resistance is not infinite or close to zero, the crystal may have a leak or be broken.

This method only checks for leaks. If the crystal is open internally, this method won’t detect it. In such cases, the following methods should 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 taken from a small seven-pin or nine-pin tube socket. It is better to choose high-brightness LEDs for better visibility.

When testing the quartz crystal, insert its two pins into the XS1 and XS2 sockets, then press the switch SB. If the crystal is good, the oscillation circuit made of components like the transistor VT1, C1, C2, etc., will oscillate. The oscillating signal is coupled to VD2 through C3, and the detected DC signal turns on VT2, causing the LED connected in the collector circuit of VT2 to light up, indicating the crystal is good. If the LED doesn't light up, the crystal is faulty. This tester can work over a wide frequency range, but it performs best between several hundred kilohertz and tens of megahertz.

Tag: Crystal Oscillator Quality Measurement Tips