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

Crystal oscillator quality measurement tips

Measuring 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. So, how can you accurately assess the quality of a crystal oscillator?

1. Use a multimeter (R × 10k range) to measure the resistance at both ends of the crystal oscillator. If it reads infinite, there is no short or leakage. Then, plug the test lead into the 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 LED lights up, the crystal is good. If not, the crystal may be damaged.

2. Use a digital capacitance meter (or a multimeter with a capacitance function) to measure its capacitance. A damaged crystal will usually show a significantly reduced capacitance value. The normal capacitance range varies depending on the crystal type, typically ranging from tens to hundreds of picofarads.

3. Bring the crystal close to your ear and gently shake it. If you hear a strange sound, it may indicate internal damage. A broken crystal might still oscillate but could produce an unstable frequency.

4. Test the output voltage of the crystal oscillator. Normally, it should be about half of the supply voltage. Since the output is a sine wave, the peak-to-peak voltage is close to the supply voltage, so a multimeter will read approximately half of that value.

5. Use 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 measure the voltage across the two pins of the crystal oscillator. If the working voltage is 5V, the reading should be around 2.5V. Additionally, if you touch one of the pins 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, the crystal is functioning properly!

Crystal Detection Methods

Resistance Method

Set the multimeter to the R×10K range 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 be leaking or shorted.

This method only detects leakage. For internal open circuits, you’ll need another approach.

2. Homemade Tester

By building a simple crystal tester, you can accurately test the quality of a crystal. You can use sockets from a small seven-legged or nine-legged tube socket. It’s better to choose high-brightness LEDs for better visibility.

When testing a crystal, insert its two pins into XS1 and XS2. Press the switch SB. If the crystal is good, the circuit composed of components like VT1, C1, C2, etc., will oscillate. The signal is coupled to VD2 through C3, turning on VT2 and lighting the LED connected to its collector, indicating a good crystal. If the LED doesn’t light, the crystal is faulty. This tester works well for crystals in the range of several hundred kilohertz to tens of megahertz.

Tag: Crystal Oscillator Quality Measurement Tips