Quartz crystal oscillator is referred to as "crystal oscillator". It is widely used in electronic clocks, walkie-talkies, single-chip microcomputers, color TV color field and field oscillation frequency dividing circuits and all infrared remote controllers. For the judgment of whether the crystal oscillator is good or bad, it is generally only possible to judge whether there is leakage, short circuit or the capacitance value between the two feet to roughly estimate its good or bad, but it is impossible to measure the frequency deviation and vibration. The instrument for measuring the crystal frequency is expensive, difficult to buy, and has low utilization.
In fact, it can be completely self-made, the cost of materials is only 10 yuan (using a color TV remote control, plus a small circuit board), the material is ready to be modified half an hour later, with the digital frequency meter, it can be accurate Measure the crystal frequency of the remote control and judge whether the remote control is good or bad.
The modification method is as follows: Disassemble the back cover of the remote control and solder the 455 kHz crystal on the circuit board. Use a double-column 8-pin IC holder as the test clip, only use a single column, 1~2, 3~4 feet are welded together and soldered on the circuit board to do the crystal vibration test clip, the purpose is to facilitate the plugging of crystals of different sizes. Use 2 waste ballpoint pens to make the frequency meter test terminal and the crystal test clip to be welded together. Test the clip and connect a 2-core shield wire to the crystal of the remote control, and use the 3V power supply on the remote control to add additional circuit. The board is powered, and the additional small circuit board has 5 lines (2 power supplies and 2 tests) to the remote controller, and the other line is connected to the remote controller IC output pin by R2 (ie, the NPN transistor B pole on the remote controller). The crystal oscillator is inserted into the test clip socket, and the LED will flash when the remote control button is pressed. If the digital frequency meter is connected, the crystal frequency of the remote control can be accurately measured.
The other remote control is aimed at the infrared photodiode button, and the LED will flash, indicating that the remote control is good.
The color TV remote control lC model is Mitsubishi M50560-OOIP, the crystal oscillator is 2 lOOpF capacitors, the frequency meter is the victory card VC920 pocket digital multimeter, the frequency range is 0-20MHz. The experiment proves that: the trap and the three-leg crystal can start to oscillate. The crystal oscillator below 1MHz can be accurately measured by the multimeter's frequency measurement function. The crystal oscillator that is larger than 1MHz will stop using the multimeter. The crystal is inserted into the remote control, and D2 in the figure below will still glow. The color TV remote control is similar, and the working principle is the same, as long as the crystal frequency is less than 7.15MHz. Other models of color TV remote control can also be processed as usual. The circuit is shown below.
The circuit below is very simple. Two NPN triodes are used to form a composite tube for amplifying the infrared light signal of the remote controller under test. D1 uses a flat infrared photodiode, D2 uses a red circular LED, R1 is a D2 current limiting resistor, and R2 is a remote control. The IC output current limiting resistor on the device, R3 and Dl form a voltage dividing circuit to vent the reverse penetration current of Dl. If there is no R3, D2 will be on. The resistor can be used 1/8W.
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