Testing electronic components by colin mitchell pdf


    Full text of "Testing Electronic Components by Colin Mitchell" Isolation Transformer Triacs LEDs Unknown resistors - testing Logic Probe The circuit for a ring tester can be found here: risigranoli.ga It sends a. Testing Electronic Components - Colin risigranoli.ga Testing Electronic Components - Colin risigranoli.ga Posted by Unknown at · Email This BlogThis!. My Arduino workfolder. Contribute to brammeke11/Arduino development by creating an account on GitHub.

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    Testing Electronic Components By Colin Mitchell Pdf

    Download Testing Electronic Components - Colin Mitchell. Recommended. Colin Mitchell - IC Circuits · Electronic Components · Electronic Components. risigranoli.ga Testing Electronic Components Ebook - The Best Review Guide Fix. How to get FREE electronic parts for projects!by Colin Mitchell It comes in 3. Download as DOC, PDF, TXT or read online from Scribd Bonus_Speedup Testing Electronic Components Analogue Multimeter Audio Stages Batteries - testing Burnt Resistor downloading A Multimeter Capacitors .. PNP $ including pack and post email Colin Mitchell for details on how to pay by credit card or PayPal.

    Talking Electronics or TE was an Australian electronics magazine from the s aimed at beginners and hobbyists, founded and produced by Colin Mitchell in Cheltenham, Australia. The magazine, and its associated mail-order kit business, operated for its entirety out of Mitchell's home. The general magazine lasted 15 official issues, but there were many one-off publications produced in addition to the issue-based magazine. The first issue was in , with the last issue being 15 in May Mitchell has since released all material, books, and issues of the magazine as public domain on his websites [2] — "Not Copyright Colin Mitchell - you can copy anything - in fact you should copy all the projects and data sheets. It is known as the first electronics magazine in the world to include a printed circuit board on the front cover. This business proved very popular, with hundreds of thousands of kits being sold. Towards the height of the magazine, Mitchell tried to take Talking Electronics to the United States, but was ultimately unsuccessful at distribution after printing , copies. These copies were eventually repackaged and sold once he returned to Australia.

    Resistors come in a range of values and the two most common are the E12 and E24 series. This is different to 4-band resistors where black represents the word OHMS! The following list covers 10 ohms 10R to 1M. The E12 series comes in twelve values for each decade. But there are a number of codes. All the SM resistors in the above photos conform to a 3-digit or 4-digit code.

    Resistances less than ohms are written: This way you cannot make a mistake when reading a value of resistance. Here is a basic 3-digit SM resistor: A k SM resistor The first two digits represent the two digits in the answer. The answer will be OHMS.

    The third digit represents the number of zero's you must place after the two digits. It consists of a three-character code. The final answer is: This is written Click to see the complete range of SM resistor markings for 4-digit code: Sometimes the resistor is marked: This is known as the EIA marking method.

    The first two digits signify the 3 significant digits of the resistor value. It is a zero-ohm LINK! Resistances less than 10 ohms have 'R' to indicate the position of the decimal point. The comma can be replaced by the letter "k". The third character. For example: Here are some examples: Three Digit Examples is 33 ohms. Always check with an ohm-meter a multimeter to make sure. Chip resistors come in the following styles and ratings: The following packs are available: If you want to create a "Special Value," simply connect two resistors and read the value with a Digital Meter.

    Keep changing the values until you get the required value. We are not going into series or Parallel formulae. You can easily find a value with a multimeter. You simply ADD the values. This can be done with any to two values as shown. Three equal-value resistors in series is three times the value.

    Three equal-value resistors in parallel is equal to one-third the value. If you want a particular value and it is not available, here is a chart. Use 2 resistors in series or parallel as shown: There are other ways to combine 2 resistors in parallel or series to get a particular value. The examples above are just one way. The surrounding components can affect the.

    You can take the reading of a resistor "in-circuit" in one direction then the other, as the surrounding components may have diodes and this will alter the reading. You can also test a resistor by feeling its temperature-rise. It is getting too hot if you cannot hold your finger on it some "metal film" resistors are designed to tolerate quite high temperatures.

    Resistors are just "resistors" and they can be in AC circuits or DC circuits. It is a low-value resistor and has a voltage-drop across it but this is not intentional. The voltage-drop is to create a "heating-effect" to burn out the resistor. In all the other types of resistor, the voltage-drop is intentional. A Ballast resistor is a normal resistor and can be called a Power resistor, Dropper resistor, Supply resistor or Feed resistor.

    It is designed to reduce the voltage from one source and deliver a lower voltage. It is a form of: A Load Resistor is generally connected across the output of a circuit and turns the energy it receives, into heat. It is made with many resistors of the same value, all in one package. One end of each resistor is connected all the other resistors and this is the common pin, identified as pin 1 and has a dot on the package.

    These packages are very reliable but to make sure all the resistors are as stated, you need to locate pin 1. All values will be identical when referenced to this pin. The 4S indicates the package contains 4 independent resistors that are not wired together inside. The housing has eight leads as shown in the second image. Independent resistors have an even number of pins and measuring between each pair will produce identical values.

    Resistance between any pair will indicate leakage and may be a fault. You can perform voltage tests and if you know the expected output voltage. You may be able to find a spot where the spiral has been damaged. This causes the current to decrease and any magnetism in the shadow mask is removed.

    This constant heat eventually destroys the package. The resistance of a "burnt" resistor can sometimes be determined by scraping away the outer coating if the resistor has a spiral of resistance-material.

    Posistors have different resistance values from different manufacturers and must be replaced with an identical type. Measure from one lead of the resistor to the end of the damaged spiral.. Many Posistors have a second element inside the case that connects directly to the supply to keep the Positive Temperature Coefficient resistor high so that the current through the degaussing coil falls to almost zero.

    Start with a very high value and turn the circuit ON. This current heats up the Posistor and the resistance increases. If you do not know the expected voltage. This process works very well for damaged wire-wound resistors. The posistor can one or two elements and it is kept warm so the resistance remains high. There is another way to determine the value of a damaged resistor.

    A Posistor is a resistor that connects in series with the degaussing coil around the picture tube or Monitor. Get a set of resistors of the same wattage as the damaged component and start with a high value. Then measure from the other lead to the other end of the spiral. It's handy to know if the resistor is in the range: You can add a small amount for the damaged section. Clean the "spot" burnt section of the spiral very carefully and make sure you can get a good contact with the spiral and the tip of your probe.

    The heavy current that flows when a set is turned ON also causes the posistor to crack and break and this results in poor purity on the screen. When cold. Add the two values and you have an approximate value for the resistor. They can be pulled apart and each section of the resistance-wire nichrome wire measured and added to get the full resistance. They can be checked for very low resistance when cold but any loose pieces inside the case will indicate a damaged component.

    By multiplying the two you will get a wattage and this must be less than the wattage of the resistor being replaced. We have already covered placing resistors and capacitors in parallel and series: Cleaning with spray fixes the bad focus but if the pot is leaking to chassis from inside the pot due to the high voltage on the terminals simply remove it from the chassis and leave it floating this will restore the high voltage to the picture tube or you can use one from an old chassis.

    Two 1k 0. A Rheostat is a variable resistor using only one end and the middle connected to a circuit. The resistance between the two outside pins is the value marked on the component and the centre leg will change from nearly zero to the full resistance as the shaft is rotated. Zener diodes can be connected in series to get a higher voltage.

    Two inductors in series. There is a third way to determine the value and this requires measuring the voltage drop across the resistor and the current-flow.

    The "resistance of a circuit" may be very low as the electrolytics in the circuit are uncharged. When taking a reading. Set the pointer to "0" right end of the scale by touching the probes together and adjusting the "zero ohms" control.

    This may not indicate a true "short-circuit. You can use the resistance scale "x1" or "x10" to detect low values of resistance. Leads and wires and cords have a small resistance and depending on the length of the lead.

    This is the best advice in a situation where you do not know the value of a resistor. Two 12v zener diodes in series produces a 24v zener. This is ideal when testing logic circuits as it is quick and you can listen for the beep while concentrating on the probe. This is done by measuring them on a low OHMs range in one direction then reverse the leads to see if the resistance is low in the other direction. Before re-connecting the supply.

    Free PDF Testing Electronic Components

    The following circuit has the advantage of providing a beep when a short-circuit is detected but does not detect the small voltage drop across a diode. Depending on the rating of the fuse. They are all current ratings as a fuse does not have a voltage rating.

    This proves they are working. An overload can occur when the supply voltage rises to nearly full voltage. Some fuses are fast-blow and some are slow-blow. That's why a 12v battery supplying a circuit with these leads will have 11v at the circuit. Turn off all power to the equipment before testing for shorts and continuity. If the battery is You will need lots of "Test Equipment" and they can be built from circuits in this eBook.

    This indicates a very high current has passed through the fuse. When taking readings in a circuit that has a number of diodes built-into IC's Integrated Circuits and transistors.

    All fuses. A fuse can be designed for 50mA. Turn off the equipment before making any continuity tests. Using a multimeter is much slower. By making the lead shorter or using thicker wire. Some fuses are designed for cars as they fit into the special fuse holders. Remember this: When a circuit takes 1 amp.

    The presence of even a small voltage from an electrolytic can give a false reading. If the inside of the glass tube of the fuse is totally blackened.

    A reading can be very low at the start because electrolytics need time to charge-up and if the reading gradually increases. You can determine the resistance of a lead very accurately by taking the example above and applying it to your circuit.

    An inductor with a shorted turn will have a very low or zero inductance. This causes the fuse to "blow. The solution is to measure a larger inductor and note the reading. You can then compare the inductance with a known good component. You can try another fuse to see what happens. This is the section that will "burn-out.

    If the current increases to 2amps. When a circuit is turned on. Or it may be a loop of wire that is thin near the middle of the fuse. It needs about 3 amp to heat up the wire to red-hot and burn out. The way it works is a discussion for another eBook. If the current increases to 5 amp. A "normal" fuse consists of a length of thin wire. You can test this component for continuity between the ends of the winding and also make sure there is no continuity between the winding and the core.

    However these components can become intermittent due to dirt or pitting of the surface of the contacts due to arcing as the switch is opened. But you cannot replace a slow-blow fuse with a fast acting fuse as it will be damaged slightly each time the equipment is turned on and eventually fail.

    You can replace a fast-acting fuse normal fuse with a slow blow if the fast-acting fuse has been replaced a few times due to deterioration when the equipment is turned on. The winding can be less than one ohm.

    It will then protect a power supply from delivering a high current to a circuit that has failed. Sometimes one of the pieces of wire is a spring and when the current rises to 2. This way you can measure very small inductors.

    Thus the fuse is not gradually being damaged and it will remain in a perfect state for a long period of time. A TV or monitor screen is the best piece of Test Equipment as it has identified the fault. A fuse does not protect electronic equipment from failing. It is pointless trying to test the windings further as you will not be able to test them under full operating conditions. A slow-blow fuse uses a slightly thicker piece of wire and the fuse is made of two pieces of wire joined in the middle with a dob of low-temperature solder.

    The wire may be wrapped around a core made of iron or ferrite. If a slow-blow fuse has melted the solder. It is labeled "L" on a circuit board. An electromagnetic relay is a switch operated by magnetic force. There are many different types of relays and basically they can be put into two groups. This causes more arcing and eventually the switch heats up and starts to burn.

    They store energy when the supply-voltage is present and release it when the supply drops. 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. It is best to test these items when the operating voltage and current is present as they quite often fail due to the arcing. A switch can work 49 times then fail on each 50th operation. Connect 5v or 12v to the coil or 24v and listen for the "click" of the points closing.

    The contacts allow a current to flow and this current can damage the contacts. You really need to put a load on the points to see if they are clean and can carry a current. A capacitor works in exactly the same way. Suppose you have a strong magnet on one side of a door and a piece of metal on the other.

    The same with a relay. That's because they don't give a reading on a multimeter and their value can range from 1p to Both are correct and you have to combine them to get a full picture. If the contacts do not touch each other with a large amount of force and with a large amount of the metal touching.

    The next concept is this: Capacitors are equivalent to a tiny rechargeable battery. An electronic relay Solid State Relay does not have a winding. The relay opens and closes a set of contacts. This needs more explaining.

    The metal can be connected to a pump and you can pump water by sliding the magnet up and down. Measure the resistance across the points to see if they are closing. A relay also has a set of contacts that can cause problems.

    It works just like the magnetic field of the magnet through a door. The LED illuminates and activates a light-sensitive device. The coil will work in either direction.

    These two concepts can be used in many ways and that's why capacitors perform tasks such as filtering. This force is generated by current through a coil. A faulty capacitor may be "open" when measured with a multimeter. If not. But it works in another way. This means no current flows through a capacitor. By sliding the magnet up and down the door. If you raise a voltage on one lead of a capacitor.

    Switches are the biggest causes of fire in electrical equipment and households. Smaller capacitors are ceramic and they look like the following. This is a n ceramic: To read the value on a capacitor you need to know a few facts.

    Most electronic circuits use capacitors with smaller values such as 1p to 1. C This is the value used in all equations. A 1 microfarad capacitor is about 1cm long and the diagram shows a 1u electrolytic. The easiest way to understand capacitor values is to start with a value of 1u. This is one microfarad and is one-millionth of a Farad. There are many different sizes. It must be very thin to keep things small. This is especially true for surface-mount capacitors.

    If this happens. All capacitors are marked with a value and the basic unit is: They are all the same. If a capacitor sees a voltage higher than its rating. The two plates can be stacked in layers or rolled together. They must be fitted so the positive lead goes to the supply voltage and the negative lead goes to ground or earth. They consist of two plates with an insulating material between. Capacitors from 1p to n are non-polar and can be inserted into a circuit around either way.

    Capacitors from 1u to The important factor is the insulating material. Simply replace with exactly the same type and value. For testing and repair work. A tantalum is smaller for the same rating as an electrolytic and has a better ability at delivering a current. If you replace an electrolytic with a "miniature" version.

    This current heats up the electrolytic and that is why some electrolytics are much larger than others. The "voltage" or "working voltage" can be: Electrolytics are available in 1u.

    There is also another important factor that is rarely covered in text books. They are available up to about 1. 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. This is the amount of current that can enter and leave an electrolytic.

    Sometimes the leads are not identified. If you do not have the exact value. 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. It sometimes has the letters "NP" on the component. 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.

    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.

    In the circuit below. Use a 1k 3watt or 5watt resistor on jumper leads and keep them connected for a few seconds to fully discharge the electro. You can test capacitors in-circuit for short-circuits.

    A short-circuit within the capacitor 2. Use the x1 ohms range. Capacitors connected in parallel will produce a larger-value capacitance. Electrolytic capacitors are commonly available in 6v. Values below 1u will not respond to charging and the needle will not deflect. This indicates it has been charged.

    For values above 1u you can determine if the capacitor is charging by using an analogue meter. You can reverse the probes to see if the needle moves in the opposite direction. Before testing any capacitors. Capacitor values above 1u. These capacitors are in power supplies and some have a resistor across them. Swelling at the top of an electrolytic indicates heating and pressure inside the case and will result in drying out of the electrolyte.

    The needle will initially move across the scale to indicate the cap is charging. If a bleed resistor is not present the cap can retain a charge after the equipment is unplugged. Here are examples of two equal capacitors connected in series or parallel and the results they produce: Test it with a voltmeter to make sure all the energy has been removed.

    High voltage electrolytic caps can pose a safety hazard. Use the x10k range on an analogue or digital multimeter. This specifies the maximum voltage that can be applied across the capacitor without puncturing the dielectric.

    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. Any hot or warm electrolytic indicates leakage and ceramic capacitors with portions missing indicates something has gone wrong. Ceramic capacitors with ratings of 1kv to 5kv are also available. This does not work with a digital meter as the resistance range does not output any current and the electrolytic does not charge.

    To test a capacitor for leakage. Capacitors connected in series will produce one with a higher voltage rating. Voltage ratings for "poly. Here is a simple circuit that can be added to your meter to read capacitor values from 10p to 10u. No capacitor is perfect and when it gets charged or discharged. The full article can be found HERE.

    However if you get more than one repair with identical faults. In most cases. Capacitors can produce very unusual faults and no piece of test equipment is going to detect the problem. The author has fixed TV's and fax machines where the capacitors have been inferior and alternate types have solved the problem. This is due to the way it is constructed. This effectively makes the capacitor slightly slower to charge and discharge.

    Some capacitors are large while others are small. 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. They all react differently when the voltage fluctuates. If the Test Equipment says the component is ok. Rather than spending money on a capacitance meter.

    Some capacitors are simply plates of metal film while others are wound in a coil. 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. You can completely destroy the operation of a circuit by selecting the wrong type of capacitor. It is complete madness to even think of testing critical components such as capacitors.

    Not only this. 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. This position represents the voltage drop across the junction of the diode and is NOT a resistance value.

    It will not allow any current to flow. This is due to the different junction voltage drops. Open circuit in both directions. The technical term for this is the diode is reverse biased. When the diode is connected around the other way. 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: The technical term for this is the diode is forward biased.

    When the diode is measured in one direction. Low resistance in both directions. If you change the resistance range. Breakdown under load. Thus the needle will not move. Some capacitor are suitable for high frequencies. The needle will swing to a slightly different position for a "normal diode" compared to a Schottky diode.

    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.

    This indicates the diode is not faulty. This is because a diode has a number of characteristics that cannot be tested with simple equipment. The following diagrams show different types of diodes: A diode can go open under full load conditions and perform intermittently. Other diodes have a low drop across them and if an ordinary is used.

    Some diodes have a fast recovery for use in high frequency circuits. The best thing to do with a "suspect" diode is to replace it.

    The output of the circuit will be low and sometimes the diode heats up more than normal. The line on the end of the body of a diode indicates the cathode and you cannot say "this is the positive lead. If the diode is replaced with an ordinary diode. A leaky diode can be detected by a low reading in one direction and a slight reading the other direction.

    Most diodes fail by going: This can be detected by a low resistance x1 or x10 Ohms range in both directions. They conduct very quickly and turn off very quickly so the waveform is processed accurately and efficiently. To locate this fault. The cathode is defined as the electrode or lead through which an electric current flows out of a device.

    They are also available in pairs that look like a 3-leaded transistor.

    Diodes come in pairs in surface-mount packages and 4 diodes can be found in a bridge. However this type of fault can only be detected when the circuit is working.

    The electrolytics charge during the peaks and deliver energy when the diode is not delivering current. The v AC called the "mains" consists of two wires. Suppose you touch both wires. It is a v shock. This is shown on the output of the Power Diode.

    The diagram shows an AC waveform on the output of the secondary. The bottom lead is called "zero volts. 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. This is how the output becomes a steady DC voltage. 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.

    The diode only conducts when the voltage is "above zero" actually when it is 0. You will get a shock. This is shown in the diagram below. You never get a v shock. We now transfer this concept to the output of a transformer. It can also be called a "Reverse-Voltage Protection Diode. Whenever a magnetic filed collapses. This is the principle of a flyback circuit or EHT circuit. As we mentioned before. When reading in the LOW direction. 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.

    Testing Electronic Components by Colin Mitchell

    The diode is placed so that the signal passes through it and less than 0. There is no piece of test equipment capable of testing a diode fully. A damper diode can be placed across the coil of a relay. The quickest. It does not have to be a high-voltage diode as the high voltage in the circuit is being absorbed by the diode. Since Silicon. This does not represent one diode being better than the other or capable of handling a higher current or any other feature. The high voltage comes from the transformer.

    Germanium and Schottky Diodes have slightly different characteristic voltage drops across the junction. They are used in remote controls and to see if they are working. Orange LEDs are about 2. An LED needs about 2v. For instance a 1N is a v zener diode as this is its reverse breakdown voltage.

    A Digital meter can produce false readings as it does not apply enough current to activate the junction. You can measure this voltage if you want to match two or more LEDs for identical operation. It is the crystal that produces the colour and you need to replace a LED with the same quality to achieve the same illumination. You must have a resistor in series with the LED to limit the current.

    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 illumination produced by a LED is determined by the quality of the crystal. 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.

    They are one of the most heat-sensitive components. A bad diode will read zero volts in both directions. The value of the resistor must be selected so the current is between 2mA and 25mA. However a simple tester can be made by joining 3 cells together with a R resistor and 2 alligator clips: The LED does not emit light when it is revered-biased. For a germanium diode. Never connect a LED across a battery such as 6v or 9v. And a zener diode can be used as an ordinary diode in a circuit with a voltage that is below the zener value.

    Using this.

    Colin Mitchell - IC Circuits | Electronic Circuits | Electrical Engineering

    LEDs rarely fail but they are very sensitive to heat and they must be soldered and de-soldered quickly. The colour of the LED will determine the voltage across it. The life expectancy of a LED is about Red LEDs are generally 1. It is used as a low current indicator in many types of consumer and industrial equipment.

    Fortunately almost every digital multimeter has a diode test mode. The light produced by a LED can be visible. The same with the other half-cycle. If we use 18v zeners. The circuit will test up to 56v zeners. It uses 3 ordinary diodes to increase the output voltage of a 3-terminal regulator by 2.

    Connect the zener across the supply with a 1k to 4k7 resistor and measure the voltage across the diode. If we put 2 zener diodes in a bridge with two ordinary power diodes. Most diodes have a reverse breakdown voltage above v. If the reading is high or low in both directions.

    This means the current being supplied to a circuit must also be available from the circuit supplying the regulator. This is what we have done. See the diagram above. The output is 17v4. A regulator can only decrease the voltage. To tests a zener diode you need a power supply about 10v higher than the zener of the diode.

    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. All regulators have different pin-outs. This allows the right zener to pass current just like a normal diode. A 24v zener can be created by using two 12v zeners in series and a normal diode has a characteristic voltage of 0.

    If a regulator is not getting hot or warm it has either failed or the circuit is not operating. Providing the input voltage is 4v above the output voltage. This clever design uses 4 diodes in a bridge to produce a fixed voltage power supply capable of supplying 35mA. The concept only works in the circuit above. Here is a zener diode tester. It cannot increase the current. This can be used to increase the voltage of a zener diode by 0.

    If it measures less than 1v. Winding B C becomes a separate winding as shown in the second diagram. The bottom and top layers touch at the point shown in the diagram and the current that originally passed though A. When two turns touch each other. Almost no voltage will be detected from winding. A tester is not going to find this fault.

    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 the output wires of a transformer are shorted together. However when a transformer or coil is measured with an inductance meter. With the power turned off or the regulator removed from the circuit. IF transformers. EHT transformers flyback transformers. All these devices can go faulty. This includes chokes.

    This is done with the transformer removed from the circuit and this can be a very difficult thing to do. The inductance meter reads this and produces a value of inductance in Henry milliHenry or microHenry. If the coil or transformer has a shorted turn. However there is one major problem with measuring a faulty transformer or coil. The winding becomes two separate windings. The reading from the inductance meter will be low or very low and you have to work out if it is correct.

    The circuit for a ring tester can be found here: The voltage between the turns may be sparking or jumping a gap and creating a problem. Some regulators will work with a difference as low as 1v. 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. This short-circuit causes the transformer to get very hot.

    We will take the case of a single winding such as a coil. You will only get one or two return pulses. This is shown in the first diagram above and the winding is wound across a former and back again. If any resistance readings are very low or zero ohms.

    It may only become faulty when power is applied. One way to detect a faulty power transformer is to connect it to the supply and feel the temperaturerise when nothing is connected to the secondary. Working on exposed "mains" devices is extremely nerve-wracking and you have to very careful. Detecting shorted turns is not easy to diagnose as you really need another identical component to compare the results.

    Many electrical appliances are fully insulated and only have two leads connected to the mains. The current capability of the secondary winding does not matter. I am not suggesting you carry out the following tests. If you are working on a project. You can use any transformers providing the primary and secondary voltages are the same. If the secondaries are not equal.

    However if you want a supply that has almost the same voltage as your "Mains. Most transformers get very hot when a shorted turn has developed. To be on the safe-side. Since the transformer will take almost no current when not loaded.

    However when the appliance is connected to the main via an isolation transformer. This handy isolation transformer will provide you with "Mains Voltage" but with a limited current. You must be sure it is a mains transformer designed for operation on 50Hz or 60Hz. If you are using two transformers with different VA ratings. It should NOT get hot. In other words it will have a limited capability to supply "wattage.

    This has some advantages and some disadvantages. Measure the input AC voltage and output AC voltage. Colin Mitchell designs a lot of "LED lighting lamps" that are connected directly to the mains. He always works with an isolating transformer. If you touch a soldering iron on the "live" active end of the heating element it will cause a shortcircuit. When you take these appliances apart.

    As soon as you earth one lead of the output an isolation transformer. Switch-Mode transformers operate at frequencies 40kHz and higher and are not covered in this discussion. It may deliver a voltage but the heat generated and a smell from the transformer will indicate a fault.

    If the transformer has loaded your isolating transformer it will be faulty. You can check the "quality" of the transformer. The signal is applied to the LED.

    A common opto-coupler is 4N Once you have the weight of the transformer and the output voltage. Mains transformers are approx 15 VA for gm. If the transformer is 15VA and the output voltage will be 15v AC. The 4N35 opto-coupler schematic is shown below: You need to set-up the test-circuit shown above with a 1k resistor on the input and 1k5 on the output.

    The opto-coupler should be removed from circuit to perform this test. It is used to allow two circuits to exchange signals yet remain electrically isolated. For transformers up to 30vA. TRIAC's and other semiconductor devices as an output. The light is proportional to the signal. VA stands for Volts-Amps and is similar to saying watts. When the 1k is connected to 12v. If the transformer has a number of secondaries.

    Watts is used for DC circuits. For an NPN transistor. Programmable Unijunction Transistor and others. 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.

    As the voltage is increased on the base. The only difference is the amount of amplification they provide. And the only other slight difference between transistors is the fact that some have inbuilt diodes and resistors to simplify the rest of the circuit. Base b. Since a transistor is capable of amplifying a signal. If the base is delivered 0.

    All transistors are the same but we talk about digital and analogue transistors. At about 0. There is no difference between the two. If the voltage on the base is 0v. As the voltage is increased. Components such as resistors. For simple testing purposes. The difference is the circuit. Collector c. All transistors work the same way. The symbols have been drawn exactly as they appear on a circuit diagram.

    You can download the book so you can read it later. To do this you need. You really need both types to cover the number of tests needed for designing and. An electronic circuit is composed of various types of components. Becomes devoid of free. Secrets given should only be carried out by suitably qualified electronics. Gregs Basic Electronics book store with free download pdf electronic project tutorial books.

    This book provides an excellent introduction to electronic circuit design. The text is divided into two parts. Part I provides. Counterfeit electronic components free download c programs pdf are electronic parts that are. It is enabled through two PDF forms that are free to use. Agency Kemi and Electrical Safety Authority tested 63 consumer electronics products and. The tests need not be elaborate, for example, switching an electronic or electrical system.

    Limit on using screens when testing compact electronic assemblies. Perform whisker testing experiments on electronic boards. Mixed technology issues eg Pb-contamination Post-aging tests.

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