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How to test Crystal?

Discussion in 'Electronic Repair' started by Techman, Oct 26, 2007.

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  1. Techman

    Techman Guest

    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 begin to
    vary, the electronic equipments might show intermittent faults or
    might stop altogether. The microprocessor pins that hold the crystal
    are usually called OSC IN and OSC OUT as shown in Figure 1 and the
    frequency is marked on the crystal. Typical examples of crystal
    oscillator frequency are 3.58MHZ, 4MHZ, 8MHZ, 24MHZ etc.

    Testing Crystal

    Crystals are quite fragile components because of their construction.
    Unlike a resistor or capacitor, if you drop one on the ground from a
    decent height, its 50-50 bet whether it will work again. Testing the
    crystal is not a breeze either. You cannot just take out your trusty
    multimeter and plug the crystal in it. In fact, there are three right
    ways to test a crystal.

    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 should solve the problem since
    microprocessors are usually very reliable. Check the crystal with
    power on.

    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
    and read the measurement. Be sure that your frequency counter meter
    has the range that is higher than the crystal frequency you are

    Crystal CheckerWith this method, usually the crystal is placed in the
    feedback network of a transistor oscillator. If it oscillates and the
    LED is lighten up, this mean that the crystal is working. If the
    crystal doesn't work, the LED stays off. Instead of using LED, some
    other crystal checker uses a panel meter to indicate if the crystal is
    working or not.

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