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Testing Electronic. Components You cannot give this E-book away for free. You do not reproduced or transmitted in any form whatsoever, electronic, or mechanical . brightness is raised, usually the high voltage will go-down, and when. Testing components properly is an essential basic electronic skill. A sensitive FET Download A Copy For Yourself, right now for only cents. On March 17 . Pages·· MB·28, Downloads. 1 -. Basic concepts, definitions and identities. Number System. Test of divisibility: 1. A number Basic concepts.

Free pdf testing electronic components AxesoWEB. How to get FREE electronic parts for projects! 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.

Then measure from the other lead to the other end of the spiral. This causes the current to decrease and any magnetism in the shadow mask is removed. Measure from one lead of the resistor to the end of the damaged spiral. There is another way to determine the value of a damaged resistor. When cold. They can be pulled apart and each section of the resistance-wire nichrome wire measured and added to get the full resistance. The posistor can one or two elements and it is kept warm so the resistance remains high.

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. Add the two values and you have an approximate value for the resistor.

You can perform voltage tests and if you know the expected output voltage. This process works very well for damaged wire-wound resistors. They can be checked for very low resistance when cold but any loose pieces inside the case will indicate a damaged component.

You can add a small amount for the damaged section.. A Posistor is a resistor that connects in series with the degaussing coil around the picture tube or Monitor. Start with a very high value and turn the circuit ON. This constant heat eventually destroys the package. 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. You may be able to find a spot where the spiral has been damaged. 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.

It's handy to know if the resistor is in the range: Posistors have different resistance values from different manufacturers and must be replaced with an identical type. Two inductors in series. Two 12v zener diodes in series produces a 24v zener. By multiplying the two you will get a wattage and this must be less than the wattage of the resistor being replaced. There is a third way to determine the value and this requires measuring the voltage drop across the resistor and the current-flow.

You can use the resistance scale "x1" or "x10" to detect low values of resistance. 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. 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. Zener diodes can be connected in series to get a higher voltage.

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.

We have already covered placing resistors and capacitors in parallel and series: The "resistance of a circuit" may be very low as the electrolytics in the circuit are uncharged. When taking a reading. 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.

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. If the inside of the glass tube of the fuse is totally blackened. You will need lots of "Test Equipment" and they can be built from circuits in this eBook. This proves they are working. All fuses. Using a multimeter is much slower.

Before re-connecting the supply. 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. When taking readings in a circuit that has a number of diodes built-into IC's Integrated Circuits and transistors. A reading can be very low at the start because electrolytics need time to charge-up and if the reading gradually increases.

Some fuses are fast-blow and some are slow-blow. They are all current ratings as a fuse does not have a voltage rating. The presence of even a small voltage from an electrolytic can give a false reading.

That's why a 12v battery supplying a circuit with these leads will have 11v at the circuit. Some fuses are designed for cars as they fit into the special fuse holders. Depending on the rating of the fuse. This indicates a very high current has passed through the fuse. Remember this: When a circuit takes 1 amp. By making the lead shorter or using thicker wire. This is ideal when testing logic circuits as it is quick and you can listen for the beep while concentrating on the probe.

Turn off the equipment before making any continuity tests. If the battery is A fuse can be designed for 50mA. Turn off all power to the equipment before testing for shorts and continuity. An overload can occur when the supply voltage rises to nearly full voltage.

You can determine the resistance of a lead very accurately by taking the example above and applying it to your circuit. 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. It is labeled "L" on a circuit board. A TV or monitor screen is the best piece of Test Equipment as it has identified the fault.

If the current increases to 2amps. An inductor with a shorted turn will have a very low or zero inductance. It needs about 3 amp to heat up the wire to red-hot and burn out. 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.

You can then compare the inductance with a known good component. The solution is to measure a larger inductor and note the reading. Thus the fuse is not gradually being damaged and it will remain in a perfect state for a long period of time. A fuse does not protect electronic equipment from failing. 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.

This is the section that will "burn-out. It is pointless trying to test the windings further as you will not be able to test them under full operating conditions. If the current increases to 5 amp. This way you can measure very small inductors. 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.

The wire may be wrapped around a core made of iron or ferrite. Or it may be a loop of wire that is thin near the middle of the fuse. The way it works is a discussion for another eBook. 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.

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You can try another fuse to see what happens. This causes the fuse to "blow. A "normal" fuse consists of a length of thin wire. The winding can be less than one ohm.

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. If a slow-blow fuse has melted the solder. When a circuit is turned on. They store energy when the supply-voltage is present and release it when the supply drops. Both are correct and you have to combine them to get a full picture.

A capacitor works in exactly the same way. Connect 5v or 12v to the coil or 24v and listen for the "click" of the points closing. This force is generated by current through a coil. 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 next concept is this: Capacitors are equivalent to a tiny rechargeable battery. This causes more arcing and eventually the switch heats up and starts to burn.

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. The coil will work in either direction. The relay opens and closes a set of contacts. If the contacts do not touch each other with a large amount of force and with a large amount of the metal touching. An electromagnetic relay is a switch operated by magnetic force.

This needs more explaining. The LED illuminates and activates a light-sensitive device. These two concepts can be used in many ways and that's why capacitors perform tasks such as filtering. That's because they don't give a reading on a multimeter and their value can range from 1p to If not. A faulty capacitor may be "open" when measured with a multimeter.

The same with a relay. This means no current flows through a capacitor. But it works in another way. 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.

An electronic relay Solid State Relay does not have a winding. There are many different types of relays and basically they can be put into two groups. If you raise a voltage on one lead of a capacitor. Switches are the biggest causes of fire in electrical equipment and households. A relay also has a set of contacts that can cause problems. The contacts allow a current to flow and this current can damage the contacts. It works just like the magnetic field of the magnet through a door.

You really need to put a load on the points to see if they are clean and can carry a current. 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.

Most electronic circuits use capacitors with smaller values such as 1p to 1. Smaller capacitors are ceramic and they look like the following. A 1 microfarad capacitor is about 1cm long and the diagram shows a 1u electrolytic. C This is the value used in all equations. This is one microfarad and is one-millionth of a Farad. The easiest way to understand capacitor values is to start with a value of 1u.

This is a n ceramic: To read the value on a capacitor you need to know a few facts. They are all the same. It must be very thin to keep things small. If a capacitor sees a voltage higher than its rating. If this happens.

Capacitors from 1u to There are many different sizes. All capacitors are marked with a value and the basic unit is: The two plates can be stacked in layers or rolled together. This is especially true for surface-mount capacitors. The important factor is the insulating material. Capacitors from 1p to n are non-polar and can be inserted into a circuit around either way. They consist of two plates with an insulating material between.

They must be fitted so the positive lead goes to the supply voltage and the negative lead goes to ground or earth. Simply replace with exactly the same type and value. For testing and repair work. 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. There is also another important factor that is rarely covered in text books.

The "voltage" or "working voltage" can be: If you replace an electrolytic with a "miniature" version. This is the amount of current that can enter and leave an electrolytic. A tantalum is smaller for the same rating as an electrolytic and has a better ability at delivering a current. Electrolytics are available in 1u. They are available up to about 1. This current heats up the electrolytic and that is why some electrolytics are much larger than others. 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.

It sometimes has the letters "NP" on the component. 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. Sometimes the leads are not identified.

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. In the circuit below. If you do not have the exact value. This specifies the maximum voltage that can be applied across the capacitor without puncturing the dielectric. Voltage ratings for "poly.

Capacitors connected in parallel will produce a larger-value capacitance. Capacitors connected in series will produce one with a higher voltage rating.

For values above 1u you can determine if the capacitor is charging by using an analogue meter. A short-circuit within the capacitor 2. 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. To test a capacitor for leakage. 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. Test it with a voltmeter to make sure all the energy has been removed. If a bleed resistor is not present the cap can retain a charge after the equipment is unplugged.

These capacitors are in power supplies and some have a resistor across them.

High voltage electrolytic caps can pose a safety hazard. Use the x1 ohms range. Values below 1u will not respond to charging and the needle will not deflect. Use the x10k range on an analogue or digital multimeter. Electrolytic capacitors are commonly available in 6v. Before testing any capacitors. Use a 1k 3watt or 5watt resistor on jumper leads and keep them connected for a few seconds to fully discharge the electro. Any hot or warm electrolytic indicates leakage and ceramic capacitors with portions missing indicates something has gone wrong.

Capacitor values above 1u. This does not work with a digital meter as the resistance range does not output any current and the electrolytic does not charge. Ceramic capacitors with ratings of 1kv to 5kv are also available. You can reverse the probes to see if the needle moves in the opposite direction. You can test capacitors in-circuit for short-circuits. Here are examples of two equal capacitors connected in series or parallel and the results they produce: This indicates it has been charged.

In most cases. It is complete madness to even think of testing critical components such as capacitors. Not only this. Some capacitors are large while others are small. Some capacitors are simply plates of metal film while others are wound in a coil. This effectively makes the capacitor slightly slower to charge and discharge. You can completely destroy the operation of a circuit by selecting the wrong type of capacitor.

If the Test Equipment says the component is ok. The full article can be found HERE. Here is a simple circuit that can be added to your meter to read capacitor values from 10p to 10u. A manufacturer may have taken years to select the right type of capacitor due to previous failures. 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.

This is due to the way it is constructed. You are fooling yourself. They all react differently when the voltage fluctuates. The author has fixed TV's and fax machines where the capacitors have been inferior and alternate types have solved the problem. Capacitors can produce very unusual faults and no piece of test equipment is going to detect the problem. A capacitor just doesn't have a "value of capacitance. 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.

A capacitor may be slightly important in a circuit or it might be extremely critical. No capacitor is perfect and when it gets charged or discharged. Rather than spending money on a capacitance meter. However if you get more than one repair with identical faults. When the diode is connected around the other way. When the diode is measured in one direction. 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.

Thus the needle will not move. This is due to the different junction voltage drops. 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 reverse biased. Some capacitor are suitable for high frequencies. Low resistance in both directions. This position represents the voltage drop across the junction of the diode and is NOT a resistance value.

The needle will swing to a slightly different position for a "normal diode" compared to a Schottky diode. The technical term for this is the diode is forward biased. Open circuit in both directions. It will not allow any current to flow. If you change the resistance range. This indicates the diode is not faulty.

Breakdown under load. They are also available in pairs that look like a 3-leaded transistor. 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. The following diagrams show different types of diodes: The best thing to do with a "suspect" diode is to replace it.

However this type of fault can only be detected when the circuit is working. The line on the end of the body of a diode indicates the cathode and you cannot say "this is the positive lead. The output of the circuit will be low and sometimes the diode heats up more than normal. A leaky diode can be detected by a low reading in one direction and a slight reading the other direction. To locate this fault. 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. The cathode is defined as the electrode or lead through which an electric current flows out of a device. If the diode is replaced with an ordinary diode. 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. This is because a diode has a number of characteristics that cannot be tested with simple equipment.

Most diodes fail by going: This is shown in the diagram below. The diagram shows an AC waveform on the output of the secondary. This is shown on the output of the Power Diode. This is how the output becomes a steady DC voltage. Suppose you touch both wires.

You never get a v shock. It is a v shock.

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We have used it to describe how the diode works. Only the positive peaks or the positive parts of the waveform appear on the output and this is called "pulsing DC. The v AC called the "mains" consists of two wires. You will get a shock. We now transfer this concept to the output of a transformer.

The bottom lead is called "zero volts. 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 electrolytics charge during the peaks and deliver energy when the diode is not delivering current. The diode only conducts when the voltage is "above zero" actually when it is 0.

There is no piece of test equipment capable of testing a diode fully. Whenever a magnetic filed collapses. The diode is placed so that the signal passes through it and less than 0. This is the principle of a flyback circuit or EHT circuit. 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. As we mentioned before. The high voltage comes from the transformer. Germanium and Schottky Diodes have slightly different characteristic voltage drops across the junction.

The quickest. A damper diode can be placed across the coil of a relay.

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It can also be called a "Reverse-Voltage Protection Diode. 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. Since Silicon. This does not represent one diode being better than the other or capable of handling a higher current or any other feature.

For a germanium diode. The LED does not emit light when it is revered-biased. The colour of the LED will determine the voltage across it. Fortunately almost every digital multimeter has a diode test mode. They are used in remote controls and to see if they are working.

The illumination produced by a LED is determined by the quality of the crystal. Using this. Never connect a LED across a battery such as 6v or 9v. However a simple tester can be made by joining 3 cells together with a R resistor and 2 alligator clips: They are one of the most heat-sensitive components. An LED needs about 2v. You can measure this voltage if you want to match two or more LEDs for identical operation.

It is used as a low current indicator in many types of consumer and industrial equipment. For instance a 1N is a v zener diode as this is its reverse breakdown voltage. It is the crystal that produces the colour and you need to replace a LED with the same quality to achieve the same illumination. The simplest way to deliver the exact voltage is to have a supply that is higher than needed and include a voltage-dropping resistor.

You must have a resistor in series with the LED to limit the current. Orange LEDs are about 2. And a zener diode can be used as an ordinary diode in a circuit with a voltage that is below the zener value.

Red LEDs are generally 1. The light produced by a LED can be visible. LEDs rarely fail but they are very sensitive to heat and they must be soldered and de-soldered quickly. 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.

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. A Digital meter can produce false readings as it does not apply enough current to activate the junction.

The life expectancy of a LED is about The circuit will test up to 56v zeners. A regulator can only decrease the voltage. See the diagram above. The output is 17v4. A 24v zener can be created by using two 12v zeners in series and a normal diode has a characteristic voltage of 0. Providing the input voltage is 4v above the output voltage. This allows the right zener to pass current just like a normal diode. It uses 3 ordinary diodes to increase the output voltage of a 3-terminal regulator by 2.

The concept only works in the circuit above. If the reading is high or low in both directions. Here is a zener diode tester. This is what we have done. Most diodes have a reverse breakdown voltage above v. This means the current being supplied to a circuit must also be available from the circuit supplying the regulator. This can be used to increase the voltage of a zener diode by 0.

The same with the other half-cycle. If we put 2 zener diodes in a bridge with two ordinary power diodes. This clever design uses 4 diodes in a bridge to produce a fixed voltage power supply capable of supplying 35mA. Connect the zener across the supply with a 1k to 4k7 resistor and measure the voltage across the diode. If we use 18v zeners. If it measures less than 1v. 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. If a regulator is not getting hot or warm it has either failed or the circuit is not operating. All regulators have different pin-outs. It cannot increase the current. It may only become faulty when power is applied. You will only get one or two return pulses. The voltage between the turns may be sparking or jumping a gap and creating a problem.

The winding becomes two separate windings. We will take the case of a single winding such as a coil. When two turns touch each other. This is done with the transformer removed from the circuit and this can be a very difficult thing to do. With the power turned off or the regulator removed from the circuit. The coating on the wire is called insulation or "enamel" and this can crack or become overheated or damaged due to vibration or movement.

The circuit for a ring tester can be found here: Almost no voltage will be detected from winding. A tester is not going to find this fault. The reading from the inductance meter will be low or very low and you have to work out if it is correct.

This is shown in the first diagram above and the winding is wound across a former and back again. However when a transformer or coil is measured with an inductance meter. The inductance meter reads this and produces a value of inductance in Henry milliHenry or microHenry.

When the output wires of a transformer are shorted together. IF transformers. However there is one major problem with measuring a faulty transformer or coil. You need to test a voltage regulator with the power "ON". Some regulators will work with a difference as low as 1v.

All these devices can go faulty. The bottom and top layers touch at the point shown in the diagram and the current that originally passed though A.

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. If any resistance readings are very low or zero ohms. Winding B C becomes a separate winding as shown in the second diagram.

This includes chokes.

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This short-circuit causes the transformer to get very hot. EHT transformers flyback transformers. If the coil or transformer has a shorted turn. In other words it will have a limited capability to supply "wattage. 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.

However when the appliance is connected to the main via an isolation transformer. Since the transformer will take almost no current when not loaded. However if you want a supply that has almost the same voltage as your "Mains. You can use any transformers providing the primary and secondary voltages are the same.

Colin Mitchell designs a lot of "LED lighting lamps" that are connected directly to the mains. As soon as you earth one lead of the output an isolation transformer.

It may deliver a voltage but the heat generated and a smell from the transformer will indicate a fault. 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. If the secondaries are not equal.

Switch-Mode transformers operate at frequencies 40kHz and higher and are not covered in this discussion. You must be sure it is a mains transformer designed for operation on 50Hz or 60Hz. 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.

Measure the input AC voltage and output AC voltage. To be on the safe-side. Most transformers get very hot when a shorted turn has developed. If you are working on a project. This handy isolation transformer will provide you with "Mains Voltage" but with a limited current. It should NOT get hot. This has some advantages and some disadvantages. Detecting shorted turns is not easy to diagnose as you really need another identical component to compare the results. If you are using two transformers with different VA ratings.

When you take these appliances apart. The 4N35 opto-coupler schematic is shown below: The signal is applied to the LED. TRIAC's and other semiconductor devices as an output. For transformers up to 30vA. If the transformer has a number of secondaries. The light is proportional to the signal.

Once you have the weight of the transformer and the output voltage. If the transformer has loaded your isolating transformer it will be faulty. If the transformer is 15VA and the output voltage will be 15v AC. You can check the "quality" of the transformer.

VA stands for Volts-Amps and is similar to saying watts. When the 1k is connected to 12v. Watts is used for DC circuits. The opto-coupler should be removed from circuit to perform this test. A common opto-coupler is 4N You need to set-up the test-circuit shown above with a 1k resistor on the input and 1k5 on the output. It is used to allow two circuits to exchange signals yet remain electrically isolated. Mains transformers are approx 15 VA for gm.

For simple testing purposes. When the base voltage is higher than the emitter.

This eBook Shows You How to TEST COMPONENTS

At this point a very small current flows through the collector-emitter leads. 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. The symbols have been drawn exactly as they appear on a circuit diagram. The difference is the circuit.

Components such as resistors. The only difference is the amount of amplification they provide. A transistor also needs current to flow into the base to perform this amplifying function and this is the one feature that separates an ordinary transistor from a FET. As the voltage is increased on the base. As the voltage is increased.

Since a transistor is capable of amplifying a signal. Base b. There is no difference between the two. All transistors work the same way. 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.

In the following tests. That's how it works. The transistor is said to be working in its two states: OFF then ON sometimes called: Programmable Unijunction Transistor and others. In the following diagram. If the voltage on the base is 0v. Collector c. All transistors are the same but we talk about digital and analogue transistors.

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. If the base is delivered 0. For an NPN transistor.

At about 0.

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How to read: It will measure resistance values normally used to test resistors. As more current flows. We use the resistance settings. The scale starts at zero on the right and the high values are on the left. That's what this test will provide. This is opposite to all the other scales. It may have ranges such as "x10" "x" "x1k" "x10" Look at the resistance scale on the meter. Step 2. It will be the top scale. The black probe is BASE If the red probe touches a pin and the black probe produces a swing on the other two pins.

When the needle swings to "1" on the "x1k" setting. Resistance values get very close-together and very inaccurate at the high end of the scale. When the needle swings to "1" on the "x10k" setting.

Use this to work out all the other values on the scale. When the needle swings to "1" on the "x" setting. When the two probes are touched together. For a PNP transistor. This helps you see how the transistor is being turned on. This works with NPN. PNP transistors and Darlington transistors. Keep trying a transistor in all different combinations until you get one of the circuits below.

When you push on the two leads. The leads of some transistors will need to be bent so the pins are in the same positions as shown in the diagrams. Power transistors produce a lot of heat. Sometimes white compound called Heatsink Compound is used to conduct heat through the mica. They have forward and reverse voltage ratings and once these are exceeded. In some cases a high voltage will "puncture" the transistor and it will fail instantly. This draws heat away. It may appear to be burnt.

Some transistors have a metal body or fin to connect to a larger heatsink. However failures will also create shorts between all three leads. The first step in identifying a faulty transistor is to check for signs of overheating.

See Testing Mica Washers. If the transistor is connected to a heatsink with a mica sheet mica washer. In fact it will fail much faster via a voltage-spike than a current overload. The amount of heat you feel should be proportional to the size of the transistor's heat sink. Transistors can also develop an open circuit between base and collector.

Low-power signal transistors do not normally require heat sinking. This heat must be conducted away from the transistor otherwise the rise may be high enough to damage the P-N junctions inside the device. Maximum frequency of operation The replacement part should have parameters equal to or higher than the original. It may fail with a "short" between any leads. Low frequency or high frequency type.

At least the same voltage. Or a small piece of metal may be puncturing the mica. Polarity of the transistor i. A shorted transistor will allow a large current to flow.

When the equipment is switched off. The important parameters are: Points to remember: Use a desoldering pump to remove the transistor to prevent damage to the printed circuit board. Check the pinout of the replacement part. Always switch off the equipment before touching any components. Fit the heat sink. If the transistor has no heat sink. This is very important as mica is a very poor conductor of heat and the compound is needed to provide maximum thermal conduction. Advanced Analog Circuits Lectures.

Introduction to Analog Circuits. Analog Electronic Circuits Laboratory. Advances in Analog Circuits. Analysis and Design of Analog Ciruits.

Analog Electronic Circuits Lectures. Analog Circuits by Yuping Wu. Introduction to Analog Electronic Circuits.

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