Saturday, January 1, 2011

【 Weak current College 】 common electronic components testing experience 】

Electronic equipment in use with a lot of various types of electronic components, equipment failure are mostly due to the failure of or damage to electronic components. So how do you correct detection of electronic components is especially important, and this is the electronic maintenance personnel must master the skills. My electrical appliances repair has accumulated some common electronic components testing experience and skills for your reference.

1. measuring the rectifier bridge foot polarity
Multimeter reset R×1k retaining, the black table amount received any PIN bridge heap, red table pen has measured the remaining three legs, if readings are infinite, the black table amount received to the output of a Kiu heap, if reading is positive electrode 4 ~ 10 k Ω, the black table amount received PIN to bridge the heap output negative, while the remaining two pins to bridge pile of AC input.

2. determine the quality of crystal oscillator
First multimeter (R×10k retaining) measuring oscillator at both ends of the resistance value, if it is infinite, the description of the Crystal no short or leakage; then insert the power supply Jack crafty, fingers live Crystal by any of the pins, the other a crafty pins touch the top of the metal parts to crafty ne bubble red, Crystal is good; if ne bubble is not lit, the Crystal is damaged.

3. one-way thyristors detection
Available multimeter R×1k or R× 100 block of measuring any bipolar asked, reactive resistance, if you find a pair of extremely low resistance values of resistance (100 Ω ~ l k Ω), then the black table pen to control most of the red table amount received as cathode, another very positive. Thyristor total 3 pn junction, we can measure the pn junction, reactive resistor size to identify it. Measurement control extremely (G) and cathode [C) resistance, if active, reactive resistance are zero or infinity, show control extremely short circuit or open circuit; measurement control extremely (G) and anode (A) when the resistance between the positive and reverse resistance readings should be great;
(A) measuring the anode and the cathode (C) when the resistance between the positive and reverse resistance should be very large.

4. TRIAC's polarity identification
TRIAC is main electrode 1, main electrode 2 and control, if the multimeter R×1k gear measuring two primary resistance between the electrodes, the reading should approximate infinity, and the control and any main electrodes between, reactive resistance readings only dozens of Europe. According to this characteristic, it is very easy by measuring the electrical resistance between the electrodes, identify the TRIAC control. And when the black table amount received 1 main electrode. Red table amount received control very measured when the resistance is always smaller than reverse resistance, according to this we are also very easy to size by measuring the electrical resistance to identify main electrode 1 and 2 main electrode.

5. check the led digital tube or bad
First multimeter reset R×10k or R×l00k block, and then drag the red table pen and digital tube (to a total of Yin digital tube, for example) "and" leadout is connected, the black table pen loop then led other leadout, seven-segment shall respectively glow, explains digital tube is damaged.

6. criterion type MOSFET electrodes
The multimeter in R×1k retaining, using the black table pen contact assumed gate g pin, and then use the red table amount were in contact with the other two pins, the resistance is relatively small (5-10 Ω), red, black table pen Exchange measurement time. If the resistance is large (∞), instructions are reverse resistance (PN reverse), case N Groove tube, and the black table pen contact pins for gate G and the original assumption is correct. If the measurement of resistance again are very small, the description is a forward resistance, P pfet, black table amount received is gate G. If it does not appear on the above, you can swap red and black table pen, tested by the method described above, until the judgment of the grid. General type MOSFET source and drain when in manufacturing is symmetric, so when gate G determine, for source S, drain D do not have to distinguish, as the two are interchangeable. Source and drain the resistance between thousands of euro.

7. identification of the triode electrodes
For a type of marking does not clear or unmarked triode, to distinguish them three electrodes or multimeter test. First multimeter measuring range switch dial in 100 or R×1k R× suvey. Red table pens an arbitrary contact transistor electrode, the black table pen in turn contact the other two electrodes, respectively, the measurement of resistance values between them, if measured are hundreds of ' low-resistance, the red table pen contact of electrodes for base b, this tube to PNP. If the measure were dozens of first 100 kilohms high resistance, pens red table but also to contact electrode base b, this tube to NPN tube.
In distinguishing a hose and base b, based on the use of transistor forward current amplification coefficient than reverse current amplification coefficient of principles determine the collecting electrode. Any assumed an electrode for c, another electrode for the e-pole. The multimeter measuring range switch dial in R×1k electric barrier. For: PNP tube, red table pen pick c, black table amount received e-pole, then hands while kneading the tubes of b, c, but could not make the b, c, measured directly touch the two poles of a resistance. And then two table pen transposes a second measurement, measurement of resistance, twice, for: PNP-tube, the resistance of the small, red table amount received by the electrode for the collector. For NPN-type tube resistance is small, the black table amount as a collector of electrode.

8. potentiometer or bad judgement
First measuring potentiometer nominal resistance. Multimeterfor ohmmeter measured the "1" and "3" on both ends (2 "-" as the active contact), the reading should be potentiometer nominal value, such as multimeters pointer does not move, the resistance is not moving or resistance comparable to many, the potentiometer is corrupted. Then check the potentiometer activities arm and resistance of contact is good. Multimeter for ohmmeter measured the "1" and "2" or "2", "3" both ends of the hinge of the potentiometer counterclockwise rotation to close to the "off" position, the resistance should be as small as possible, and then slowly climb clock rotation axis handle resistance shall be gradually increased, to the extreme position, the resistance should be close to the potentiometer of nominal value. If the potentiometer axis knobs in the multimeter pointerThere is a bounce, connected, stroke play activities touch 』 point bad contact.
9. measuring bulk capacitor leakage resistance
Place with 500-multimeter R× R× 10 or 100, until the pointer points to the maximum value, and then immediately switch to R×1k retaining measurement, the pointer in a relatively short period of time to read out the current stable resistance.

10. distinguishing infrared receiving head pin
Multimeter reset R×1k, assume, received a head to the feet, the earth-it touches with the black table pen, pen red table respectively measuring two feet resistance, compared to twice the measure resistance (usually in the range of 4 ~ 7kQ), resistance smaller once its red table amount received for + 5V power supply pins, another resistance larger then to signal pins. On the other hand, if a table with a red pen then known tail, black table measuring known power respectively and signal feet foot, resistance is 15 k Ω or more, the resistance of the small PIN to + 5V-end, the resistance of the partial large PIN for signal-to-end. If the measurement results in line with the above resistance you can judge the received headers intact.

11. judgment unsigned Electrolytic Capacitor polarity
Discharge the capacitor short-circuit, two leader do A, B, multimeter reset R× 100 or R×1k retaining, the black table amount received A lead that red table pens B leader received until the pointer stationary after reading, after the measuring circuit discharge; the black table pens B leader received the red table amount received A lead that compare two readings, the resistance of the larger a black table amount received as cathode, red table amount received as negative.

12. measuring light-emitting diode
A capacity greater than 100 "F of electrolytic capacitors (capacity increases, the more obvious phenomenon), first with multimeter R× 100 retaining its charge, the black table pen red cathode received capacitance, received a negative electrode, the table amount of charging is completed, the black table pen grafting capacitor electrode, the measured light-emitting diode next to the red table pen and capacitance between the cathode. If the LEDs light up after getting off, indicating that it was good. At this point the red table amount received by the light-emitting diode capacitance of anode, cathode received a light emitting diode anode. If the led is not lit, it ends reversed reattach test, also is not lit, indicates that the light-emitting diode is damaged.

13. Optocoupler detection
Multimeter choose resistance R× shall not selected 100 retaining R×10k retaining, in case the battery voltage is too high breakdown of light emitting diodes. Red and black table amount received input, logging, reactive resistance, normal forward resistance 10 Ohm resistor, reverse to tens of thousands of euro kilohms. If positive, reverse resistance similar to that of light-emitting diode is damaged. Multimeter selected resistance R× 1 block. Red and black pen and then output a table, measured, reactive resistance, the normal time-averaged close to ∞, otherwise light tube is damaged. Multimeter selected resistance R× 10, red, black table amount respectively to enter, output logging led light pipes and the insulation resistance between the (conditional application of insulation resistance measuring its megohmmeter, megohmmeter output voltage should be slightly lower than the measured optical coupler allows pressure value), Luminescent tubes and light pipe insulation resistance in normal should ask to ∞.

Detection will be allocated to the multimeter R × 1 k Ω, the photosensitive by smooth and perpendicular to the incident light, thus directly in the multimeter resistance is light resistance. The complete darkness of photosensitive resistor placed, then the place measured resistance multimeter is dark. If the light resistance to several thousand euro to several dozen stem Europe, a few dark resistance to several dozen megohm, description of photosensitive is good.

15. determination of the laser diode is damaged
Remove the laser diode, measuring their resistance, resistance normally reverse should be infinity, positive resistance in 20 k Ω ~ 40 k Ω. If the log forward resistance has over 50 k Ω, laser diode degraded; if its forward resistance has more than 90 k Ω, the tube is damaged and cannot be used

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