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Full text of "Testing Electronic Components by Colin Mitchell". See other formats. This eBook shows you how to TEST COMPONENTS. Nearly all text books are also downloadable for free on "ukraine-europe.info" etc and when you see a used . Testing Electronic Components, Assemblies and Systems Page. Testing Semiconductors Without Disconnecting Them from Circuit. 1. Semiautomatic Device. CHARACTERISTICS & TESTING. INTRODUCTION. An electronic circuit is composed of various types of components. Some of these components are.

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If your non Posted January 10, 4. This article is recommended Posted May 29, 4. Repair Tips Popular Comments. April 2, 7. April 2, 6. March 26, 8. March 26, 4. March 21, Marantz Amplifier Repaired March 21, 4. January 31, August 19, June 23, It will rely heavily on the concepts of Discrete Math, but will not require any previous knowledge of the subject because all necessary math concepts will be developed in the text.

An introduction to solid state device, transmission lines and propagating electromagnetic waves. This book describes the current status of important topics in solid-state circuit technologies. The chapters are grouped under the following categories: This work introduces a reader to the basics of electronic engineering. Here, students may get their first knowledge of electronic concepts and basic components.

Emphasis is on the devices used in day-to-day consumer electronic products. John E. Whitehouse Publisher: Horwood Publishing Limited, This book covers fundamental aspects of electric circuits that form the core of many engineering disciplines. Techniques to analyze and solve electric circuits are explained in a simple manner and examples are shown to demonstrate each strategy. This book explores the behavior of semiconductor devices, to show the relation between the device material parameters, and the resulting electrical characteristics.

The text provides the link between the physics and the design of electronic circuits. Questions and answers about electronics covering several topics: Tony R. Kuphaldt Publisher: The goal was to put readable, high-quality information of industrial electronics into the hands of students.

The book was written without delving too heavy on the math, while still maintaining a lot of important information. It covers detailed command descriptions, definitions of start-up option, and a list of supported devices in the digital and analog device libraries. Let us know if these free electronics ebooks helped you out in the comments below. If you are looking for something else, check out some cool stuff. How can I say thank to you EFY.

You guys really work commendable. Always great. Thanks again Nish. Sign in Join. Sign in. This force is generated by current through a coil. The relay opens and closes a set of contacts. The contacts allow a current to flow and this current can damage the contacts. Connect 5v or 12v to the coil or 24v and listen for the "click" of the points closing.

Measure the resistance across the points to see if they are closing. You really need to put a load on the points to see if they are clean and can carry a current. The coil will work in either direction. An electronic relay Solid State Relay does not have a winding. The two pins that energise the relay the two input pins must be connected to 5v or 12v around the correct way as the voltage is driving a LED with series resistor.

The LED illuminates and activates a light-sensitive device. That's because they don't give a reading on a multimeter and their value can range from lp to ,u. A faulty capacitor may be "open" when measured with a multimeter, and a good capacitor will also be "open.

Both are correct and you have to combine them to get a full picture. This means no current flows through a capacitor. But it works in another way. Suppose you have a strong magnet on one side of a door and a piece of metal on the other.

By sliding the magnet up and down the door, the metal rises and falls. The metal can be connected to a pump and you can pump water by sliding the magnet up and down. A capacitor works in exactly the same way. If you raise a voltage on one lead of a capacitor, the other lead will rise to the same voltage. This needs more explaining - we are keeping the discussion simple. It works just like the magnetic field of the magnet through a door.

The next concept is this: Capacitors are equivalent to a tiny rechargeable battery. They store energy when the supply-voltage is present and release it when the supply drops. These two concepts can be used in many ways and that's why capacitors perform tasks such as filtering, time-delays, passing a signal from one stage to another and create many different effects in a circuit. C This is the value used in all equations, but it is a very large value.

Most electronic circuits use capacitors with smaller values such as lp to l,u. The easiest way to understand capacitor values is to start with a value of lu. This is one microfarad and is one-millionth of a Farad. A 1 microfarad capacitor is about 1cm long and the diagram shows a lu electrolytic. Smaller capacitors are ceramic and they look like the following. This is a lOOn ceramic: To read the value on a capacitor you need to know a few facts. Capacitors from lp to lOOn are non-polar and can be inserted into a circuit around either way.

Capacitors from lu to ,u are electrolytics and are polarised. They must be fitted so the positive lead goes to the supply voltage and the negative lead goes to ground or earth. There are many different sizes, shapes and types of capacitor. They are all the same. They consist of two plates with an insulating material between.

The two plates can be stacked in layers or rolled together.

Full text of "Testing Electronic Components by Colin Mitchell"

The important factor is the insulating material. It must be very thin to keep things small. If a capacitor sees a voltage higher than its rating, the voltage will "jump through" the insulating material or around it. If this happens, a carbon deposit is left behind and the capacitor becomes "leaky" or very low resistance, as carbon is conductive. This is especially true for surface-mount capacitors. All capacitors are marked with a value and the basic unit is: For testing and repair work, they are all the same.

Simply replace with exactly the same type and value. A tantalum is smaller for the same rating as an electrolytic and has a better ability at delivering a current. They are available up to about l,u, at about 50v but their cost is much higher than an electrolytic. Electrolytics are available in lu, 2u2 3u3 4u7 lOu, 22u, 47u, lOOu, u, u, u, l,u, 2,u, 3,u, 4,u, 10,u and higher.

The "voltage" or "working voltage" can be: There is also another important factor that is rarely covered in text books. This is the amount of current that can enter and leave an electrolytic. This current heats up the electrolytic and that is why some electrolytics are much larger than others, even though the capacitance and voltage-ratings are the same. If you replace an electrolytic with a "miniature" version, it will heat up and have a very short life. This is especially important in power supplies where current energy is constantly entering and exiting the electrolytic as its main purpose is to provide a smooth output from a set of diodes that delivers "pulsing DC.

It sometimes has the letters "NP" on the component. Sometimes the leads are not identified. This is an electrolytic that does not have a positive and negative lead but two leads and either lead can be connected to the positive or negative of the circuit. These electrolytics are usually connected to the output of an amplifier such as in a filter near the speaker where the signal is rising and falling. A non-polar electrolytic can be created from two ordinary electrolytics by connecting the negative leads together and the two positive leads become the new leads.

In the circuit below, the non-polar capacitor is replaced with two electrolytics. If you do not have the exact value, two or more connected in parallel or series can produce the value you need. Capacitors connected in series will produce one with a higher voltage rating. Capacitors connected in parallel will produce a larger-value capacitance.

Here are examples of two equal capacitors connected in series or parallel and the results they produce: This specifies the maximum voltage that can be applied across the capacitor without puncturing the dielectric.

Voltage ratings for "poly," mica and ceramic capacitors are typically 50v to VDC. Ceramic capacitors with ratings of lkv to 5kv are also available. Electrolytic capacitors are commonly available in 6v, lOv 16v, 25v, 50v, lOOv, v, and v ratings. CAUTION If a capacitor has a voltage rating of 63v, do not put it in a lOOv circuit as the insulation called the dielectric will be punctured and the capacitor will "short-circuit. High voltage electrolytic caps can pose a safety hazard.

These capacitors are in power supplies and some have a resistor across them, called a bleed resistor, to discharge the cap after power is switched off. If a bleed resistor is not present the cap can retain a charge after the equipment is unplugged. How to discharge a capacitor Do not use a screwdriver to short between the terminals as this will damage the capacitor internally and the screwdriver.

Use a lk 3watt or 5watt resistor on jumper leads and keep them connected for a few seconds to fully discharge the electro. Test it with a voltmeter to make sure all the energy has been removed. Before testing any capacitors, especially electrolytics, you should look to see if any are damaged, overheated or leaking. Swelling at the top of an electrolytic indicates heating and pressure inside the case and will result in drying out of the electrolyte.

Any hot or warm electrolytic indicates leakage and ceramic capacitors with portions missing indicates something has gone wrong.

A short-circuit within the capacitor 2. Capacitor values above lu. You can test capacitors in-circuit for short-circuits. Use the xl ohms range.

To test a capacitor for leakage, you need to remove it or at least one lead must be removed. Use the xlOk range on an analogue or digital multimeter. For values above lu you can determine if the capacitor is charging by using an analogue meter. The needle will initially move across the scale to indicate the cap is charging, then go to "no deflection.

You can reverse the probes to see if the needle moves in the opposite direction. This indicates it has been charged. Values below lu will not respond to charging and the needle will not deflect. This does not work with a digital meter as the resistance range does not output any current and the electrolytic does not charge.

Rather than spending money on a capacitance meter, it is cheaper to replace any suspect capacitor or electrolytic. Capacitors can produce very unusual faults and no piece of test equipment is going to detect the problem. In most cases, it is a simple matter to solder another capacitor across the suspect component and view or listen to the result.

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This saves all the worry of removing the component and testing it with equipment that cannot possibly give you an accurate reading when the full voltage and current is not present. You are fooling yourself. If the Test Equipment says the component is ok, you will look somewhere else and waste a lot of time. Here is a simple circuit that can be added to your meter to read capacitor values from lOp to lOu.

The full article can be found HERE. A capacitor may be slightly important in a circuit or it might be extremely critical.

A manufacturer may have taken years to select the right type of capacitor due to previous failures. A capacitor just doesn't have a "value of capacitance. This is due to the way it is constructed. Some capacitors are simply plates of metal fil while others are wound in a coil. Some capacitors are large while others are small. They all react differently when the voltage fluctuates. Not only this, but some capacitors are very stable and all these features go into the decision for the type of capacitor to use.

You can completely destroy the operation of a circuit by selecting the wrong type of capacitor. No capacitor is perfect and when it gets charged or discharged, it appears to have a small value of resistance in series with the value of capacitance.

This effectively makes the capacitor slightly slower to charge and discharge. We cannot go into the theory on selecting a capacitor as it would be larger than this eBook so the only solution is to replace a capacitor with an identical type. However if you get more than one repair with identical faults, you should ask other technicians if the original capacitor comes from a faulty batch.

The author has fixed TV's and fax machines where the capacitors have been inferior and alternate types have solved the problem. Some capacitor are suitable for high frequencies, others for low frequencies. Open circuit in both directions. Low resistance in both directions.

Breakdown under load. When the diode is measured in one direction, the needle will not move at all. The technical term for this is the diode is reverse biased. It will not allow any current to flow. Thus the needle will not move. This position represents the voltage drop across the junction of the diode and is NOT a resistance value. If you change the resistance range, the needle will move to a slightly different position due to the resistances inside the meter.

The technical term for this is the diode is forward biased. This indicates the diode is not faulty. The needle will swing to a slightly different position for a "normal diode" compared to Schottky diode.

This is due to the different junction voltage drops. However we are only testing the diode at very low voltage and it may break-down when fitted to a circuit due to a higher voltage being present or due to a high current flowing.

The leads of an Analogue Multimeter have the positive of the battery connected to the black probe and the readings of a "good diode" are shown in the following two diagrams: Here is the equivalent circuit: This is because a diode has a number of characteristics that cannot be tested with simple equipment. Some diodes have a fast recovery for use in high frequency circuits.

They conduct very quickly and turn off very quickly so the waveform is processed accurately and efficiently. If the diode is replaced with an ordinary diode, it will heat up as does not have the high-speed characteristic. Other diodes have a low drop across them and if an ordinary is used, it will heat up.

Most diodes fail by going: This can be detected by a low resistance xl orxlO Ohms range in both directions. To locate this fault, place an identical diode across the diode being tested. A leaky diode can be detected by a low reading in one direction and a slight reading the other direction.

However this type of fault can only be detected when the circuit is working. The output of the circuit will be low and sometimes the diode heats up more than normal. A diode can go open under full load conditions and perform intermittently. Diodes come in pairs in surface-mount packages and 4 diodes can be found in a bridge. They are also available in pairs that look like a 3-leaded transistor. The line on the end of the body of a diode indicates the cathode and you cannot say "this is the positive lead.

The cathode is defined as the electrode or lead through which an electric current flows out of a device. The following diagrams show different types of diodes: Suppose you touch both wires. You will get a shock. The neutral is connected to an earth wire or rod driven into the ground or connected to a water pipe at the point where the electricity enters the premises and you do not get a shock from the NEUTRAL.

You never get a v shock. It is a v shock. In other words, if you touch the two wires at a particular instant, you would get a POSITIVE v shock and at another instant you would get a negative v shock. This is shown in the diagram below. We now transfer this concept to the output of a transformer.

The diagram shows an AC waveform on the output of the secondary. The bottom lead is called "zero volts. The diode only conducts when the voltage is "above zero" actually when it is 0. This is shown on the output of the Power Diode. Only the positive peaks or the positive parts of the waveform appear on the output and this is called "pulsing DC. We have used it to describe how the diode works. The electrolytics charge during the peaks and deliver energy when the diode is not delivering current.

This is how the output becomes a steady DC voltage. The signal that it squelches is a voltage that is in the opposite direction to the "supply voltage" and is produced by the collapsing of a magnetic field. Whenever a magnetic filed collapses, it produces a voltage in the winding that is opposite to the supply voltage and can be much higher. This is the principle of a flyback circuit or EHT circuit.

The high voltage comes from the transformer. The diode is placed so that the signal passes through it and less than 0. A damper diode can be placed across the coil of a relay, incorporated into a transistor or FET or placed across a winding of a flyback transformer to protect the driving transistor or FET.

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It does not have to be a high-voltage diode as the high voltage in the circuit is being absorbed by the diode. When reading in the LOW direction, the needle will swing nearly full scale and the reading is not a resistance- value but a reflection of the characteristic voltage drop across the junction of the diode.

As we mentioned before, a resistance reading is really a voltage reading and the meter is measuring the voltage of the battery minus the voltage-drop across the diode. Since Silicon, Germanium and Schottky Diodes have slightly different characteristic voltage drops across the junction, you will get a slightly different reading on the scale. This does not represent one diode being better than the other or capable of handling a higher current or any other feature. The quickest, easiest and cheapest way to find, fix and solve a problem caused by a faulty diode is to replace it.

There is no piece of test equipment capable of testing a diode fully, and the circuit you are working on is actually the best piece of test equipment as it is identifying the fault UNDER LOAD.

A Digital meter can produce false readings as it does not apply enough current to activate the junction. Fortunately almost every digital multimeter has a diode test mode.

Using this, a silicon diode should read a voltage drop between 0. For a germanium diode, the reading will be lower, around 0. A bad diode will read zero volts in both directions. The LED does not emit light when it is revered-biased. It is used as a low current indicator in many types of consumer and industrial equipment, such as monitors, TV's, printers, hi-fi systems, machinery and control panels.

The light produced by a LED can be visible, such as red, green, yellow or white.

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They are used in remote controls and to see if they are working, you need to point a digital camera at the LED and view the picture on the camera screen. An LED needs about 2v - 3. The simplest way to deliver the exact voltage is to have a supply that is higher than needed and include a voltage- dropping resistor.

The value of the resistor must be selected so the current is between 2mA and 25mA. The life expectancy of a LED is about , hours. LEDs rarely fail but they are very sensitive to heat and they must be soldered and de-soldered quickly.

They are one of the most heat-sensitive components. Light emitting diodes cannot be tested with most multimeters because the characteristic voltage across them is higher than the voltage of the battery in the meter.

However a simple tester can be made by joining 3 cells together with a R resistor and 2 alligator clips: The colour of the LED will determine the voltage across it. You can measure this voltage if you want to match two or more LEDs for identical operation. Red LEDs are generally 1. Orange LEDs are about 2. The illumination produced by a LED is determined by the quality of the crystal. It is the crystal that produces the colour and you need to replace a LED with the same quality to achieve the same illumination.

Never connect a LED across a battery such as 6v or 9v , as it will be instantly damaged. You must have a resistor in series with the LED to limit the current. For instance a 1N is a v zener diode as this is its reverse breakdown voltage. And a zener diode can be used as an ordinary diode in a circuit with a voltage that is below the zener value. For instance, 20v zener diodes can be used in a 12v power supply as the voltage never reaches 20v, and the zener characteristic is never reached.

Most diodes have a reverse breakdown voltage above lOOv, while most zeners are below 70v. A 24v zener can be created by using two 12v zeners in series and a normal diode has a characteristic voltage of 0. This can be used to increase the voltage of a zener diode by 0. See the diagram above. It uses 3 ordinary diodes to increase the output voltage of a 3-terminal regulator by 2. To tests a zener diode you need a power supply about lOv higher than the zener of the diode.

Connect the zener across the supply with a lk to 4k7 resistor and measure the voltage across the diode. If it measures less than lv, reverse the zener.

If the reading is high or low in both directions, the zener is damaged. Here is a zener diode tester. The circuit will test up to 56v zeners. This clever design uses 4 diodes in a bridge to produce a fixed voltage power supply capable of supplying 35mA.

If we put 2 zener diodes in a bridge with two ordinary power diodes, the bridge will break-down at the voltage of the zener. This is what we have done.

If we use 18v zeners, the output will be 17v4. This allows the right zener to pass current just like a normal diode. The output is 17v4. The same with the other half-cycle. You cannot use this type of bridge in a normal power supply as the zener diode will "short" when the input voltage reaches the zener value. The concept only works in the circuit above. Providing the input voltage is 4v above the output voltage, the regulator will deliver a fixed output voltage with almost no ripple.

In most cases, a voltage regulator gets quite hot and for this reason it has a high failure- rate. If a regulator is not getting hot or warm it has either failed or the circuit is not operating.

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A regulator can only decrease the voltage. It cannot increase the current. This means the current being supplied to a circuit must also be available from the circuit supplying the regulator. All regulators have different pin-outs, so you need to find the input pin and output pin and make sure the voltage-difference is at least 4v.

Some regulators will work with a difference as low as lv, so you need to read the specifications for the type you are servicing. Some regulators are called "negative voltage regulators" and the input voltage will be negative and the output will be negative. You need to test a voltage regulator with the power "ON". Make sure you do not allow the probes to short any of the pins together as this will destroy the regulator or the circuit being supplied. With the power turned off or the regulator removed from the circuit, you can test it with a multimeter set to resistance to see if it is ok.

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If any resistance readings are very low or zero ohms, the regulator is damaged. This includes chokes, coils, inductors, yokes, power transformers, EHT transformers flyback transformers , switch mode transformers, isolation transformers, IF transformers, baluns, and any device that has turns of wire around a former.

All these devices can go faulty. The coating on the wire is called insulation or "enamel" and this can crack or become overheated or damaged due to vibration or movement. When two turns touch each other, a very interesting thing happens.

The winding becomes two separate windings. We will take the case of a single winding such as a coil. This is shown in the first diagram above and the winding is wound across a former and back again, making two layers.

Winding B C becomes a separate winding as shown in the second diagram. This short-circuit causes the transformer to get very hot. That's exactly what happens when any coil or transformer gets a "shorted turn. It is not possible to measure a fault like this with a multimeter as you don't know the exact resistance of a working coil or winding and the resistance of a faulty winding may be only 0.

However when a transformer or coil is measured with an inductance meter, an oscillating voltage or spike is delivered into the core as magnetic flux, then the magnetic flux collapses and passes the energy into the winding to produce a waveform.

The inductance meter reads this and produces a value of inductance in Henry milliHenry or microHenry. This is done with the transformer removed from the circuit and this can be a very difficult thing to do, as most transformers have a number of connections.

If the coil or transformer has a shorted turn, the energy from the magnetic flux will pass into the turns that are shorted and produce a current. Almost no voltage will be detected from winding. The reading from the inductance meter will be low or very low and you have to work out if it is correct.

However there is one major problem with measuring a faulty transformer or coil. It may only become faulty when power is applied. The voltage between the turns may be sparking or jumping a gap and creating a problem. A tester is not going to find this fault.

Secondly, an inductance meter may produce a reading but you do not know if the reading is correct. The circuit for a ring tester can be found here: You will only get one or two return pulses, whereas a good winding will return more pulses.

One way to detect a faulty power transformer is to connect it to the supply and feel the temperature-rise when nothing is connected to the secondary. It should NOT get hot. Detecting shorted turns is not easy to diagnose as you really need another identical component to compare the results.

Most transformers get very hot when a shorted turn has developed. It may deliver a voltage but the heat generated and a smell from the transformer will indicate a fault. Many electrical appliances are fully insulated and only have two leads connected to the mains.

When you take these appliances apart, you do not know which end of say a heating element is connected to the "live" active side of the mains and which end connects to the neutral.

I am not suggesting you carry out the following tests, but they are described to show how an isolation transformer works. If you touch a soldering iron on the "live" active end of the heating element it will cause a short-circuit. However when the appliance is connected to the main via an isolation transformer, you can touch an earthed soldering iron on either end of the heater as both leads from the isolation transformer are "floating. As soon as you earth one lead of the output an isolation transformer, the other lead becomes "active.

You can use any transformers providing the primary and secondary voltages are the same. The current capability of the secondary winding does not matter. However if you want a supply that has almost the same voltage as your "Mains," you need two transformers with the same voltages.

This handy isolation transformer will provide you with "Mains Voltage" but with a limited current. In other words it will have a limited capability to supply "wattage. This has some advantages and some disadvantages. If you are working on a project, and a short-circuit occurs, the damage will be limited to 15 watts. If you are using two transformers with different VA ratings, the lower rating will be the capability of the combination.

If the secondaries are not equal, you will get a higher or lower "Mains Voltage. Colin Mitchell designs a lot of "LED lighting lamps" that are connected directly to the mains. He always works with an isolating transformer, just to be safe. Working on exposed "mains" devices is extremely nerve-wracking and you have to very careful.

You must be sure it is a mains transformer designed for operation on 50Hz or 60Hz. Switch-Mode transformers operate at frequencies 40kHz and higher and are not covered in this discussion. To be on the safe-side, connect the unknown transformer to the output of your isolating transformer. Since the transformer will take almost no current when not loaded, the output voltages it produces will be fairly accurate.

Measure the input AC voltage and output AC voltage. If the transformer has loaded your isolating transformer it will be faulty. VA stands for Volts-Amps and is similar to saying watts. Once you have the weight of the transformer and the output voltage, you can work out the current capability of the secondary. You can check the "quality" of the transformer, the regulation by fully loading the output and measuring the final voltage.

If the transformer has a number of secondaries, the VA rating must be divided between all the windings. A common opto-coupler is 4N It is used to allow two circuits to exchange signals yet remain electrically isolated. The light is proportional to the signal, so the signal is transferred to the photo transistor to turn it on a proportional amount.

The 4N35 opto-coupler schematic is shown below: You need to set-up the test-circuit shown above with a lk resistor on the input and lk5 on the output. When the lk is connected to 12v, the output LED will illuminate.

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The opto-coupler should be removed from circuit to perform this test. A transistor is sometimes referred to as BJT Bi-polar Junction Transistor to distinguish it from other types of transistor such as Field Effect transistor, Programmable Unijunction Transistor and others. In the following diagram, two diodes are connected together and although the construction of a transistor is more complex, we see the transistor as two diodes when testing it. Base b , Collector c , and Emitter e. For an NPN transistor, the arrow on the emitter points away from the base.

It is fortunate that the arrow on both symbols points in the direction of the flow of current Conventional Current and this makes it easy to describe testing methods using our simplified set of instructions.