Crystal for Display and How to Check It

Crystal are use to keep the frequency of the clock from drifting. If the signal from this clock stops, or is weak, or the pulses start to vary, the electronic equipments might show intermittent faults or might cease altogether. The microprocessor pins that hold the crystal are usually called OSC IN & OSC OUT as shown in Figure & the frequency is marked on the crystal. Typical examples of crystal oscillator frequency are.58MHZ, 4MHZ, 8MHZ, 24MHZ etc.

Testing Crystal

Crystals are fragile parts because of their construction. Unlike a resistor or capacitor, in case you drop on the ground from a respectable height, its 50-50 bet whether it will work again. Testing the crystal is not a breeze either. You cannot take out your trusty multimeter & plug the crystal in it. In fact, there is right ways to check a crystal: -

(a) Using Oscilloscope

A crystal produces a sine wave when excited. It is appropriate then, to see a waveform representative of a sine wave on the clock pins. If the clock is not functioning properly, replace the crystal. In most cases this ought to solve the issue since microprocessors are usually reliable. Check the crystal with power on.

(b) Frequency Counter

Frequency Counter can be use to check the frequency of the crystal. The reading must be taken when the equipment power is switch "on". Place the probe of frequency counter to the crystal pin & read the measurement. Be positive that your frequency counter meter has the range that is higher than the crystal frequency you are measuring.

(c) Crystal Checker

With this process, usually the crystal is placed in the feedback network of a transistor oscillator. If it oscillates & the LED is lighten up, this means that the crystal is working. If the crystal doesn't work, the LED stays off. In lieu of using LED, some other crystal checker makes use of a panel meter to indicate if the crystal is working or not.