What is a crystal ? And how to test it.

Crystal are use to keep frequency of clock from drifting. If signal from this clock stops, or is weak, or pulses begin to vary, electronic equipments might show intermittent faults or might stop altogether. The microprocessor pins that hold crystal are usually called OSC IN and OSC OUT as shown in Figure 1 and frequency is marked on 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 ground from a decent height, its 50-50 bet whether it will work again. Testing crystal is not a breeze either. You cannot just take out your trusty multimeter and plug crystal in it. In fact, there are three right ways to test 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 clock pins. If clock is not functioning properly, replace crystal. In most cases this should solve problem since microprocessors are usually very reliable. Check crystal with power on.

How to solve multiple paper loading problem in HP5L and HP6L laser printer

Have you ever encountered before problem of having multiple paper loading in your HP LaserJet 5L and 6L? Do you know that this is caused by a defective separation pad where it's rubber has worn out. The function of separation pad is to control or allow paper to go through it, one at a time. If it spoilt, few sheets of paper will be pulled instead of one whenever you send a printer command. This sometimes will caused papers to jammed up. For worst case, it will spoil your heating/fuser sleeve. The price of a heating element is more expensive than a separation pad. There is one temporary way that you can use to solve problem stated without buying a new separation pad. The process of removing and changing separation pad is just easy and fast.