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iMac Repair Services in Dubai Call Us @ 0557503724
Apple Inc. is an American multinational technology company headquartered in Cupertino, California that designs, develops, and sells consumer electronics, computer software, and online services.
Apple revolutionized personal technology with the introduction of the Macintosh in 1984. Today, Apple leads the world in innovation with iPhone, iPad, iMac. IMac devices are an elegant, sleek and a beautiful compact designed device that offers an ultimate desktop experience provide seamless experiences across all Apple devices. IMac is the idea that draws people towards it and as it said no one can predict the possibility of iMac issues, people went through a lot of trouble/issue at that time when there is no repair services around them. So, here we come in light with 24*7 iMac repair services to resolve your issues through the onsite support.
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Resistor Color Code calculator – calculate corresponding value of a given resistor color marking
To use the resistor color code calculator click on the dropdown box starting from the left and select the corresponding color, black on the first marking is disabled by default. For the 4 band resistor calculator the third band is the multiplier and the fourth is the resistor tolerance. For the 5 band resistor calculator the 4th marking is the multiplier while the 5th marking is the tolerance, for 6 band resistor calculator the 4th marking is the multiplier, the 5th is the tolerance and the six marking is the temperature coefficient. For additional information on reading resistor color coding check out how to read resistor color code on this site. For the output value check out standard EIA Resistor value and standard value resistors.
4 BAND RESISTOR COLOR CODE AND TOLERANCE CALCULATOR
6 BAND RESISTOR COLOR CODE AND TOLERANCE CALCULATOR
The 6th band marking is the Temperature Coefficient in ppm/degreeC of a resistor which represent the amount of resistance value that will change with temperature
Table shows a list of Standard Resistor Value in plus or minus (0.5%) tolerance, (10%) tolerance, (20%) tolerance and (20%) tolerance
|Standard Resistor Value (±0.5%) tolerance|
|Standard Resistor Value (±10%) tolerance|
|Standard Resistor Value (±20%) tolerance|
|Standard Resistor Value (±20%) tolerance|
Because carbon resistors are small physically, they are color-coded to indicate their resistance value in ohms(Ω). The basis of this system is the use of colors for numerical values as listed in table 1-1 and 1-2.
In memorizing this colors, remember that the dark color, black and brown correspond to the lowest number, zero and one through lighter colors, to white for nine. The color coding is standardized by the Electronics Industries Association (EIA).
RESISTANCE COLOR BANDS.
This code is the most common system used for color coding insulated carbon resistors having axial leads, as shown above. Color band are printed at one end of the insulating body. Reading from left to right, the first color band close to the edge indicate the first digit in the numerical value of the resistance. The second band is the second digit. The Third band is the decimal multiplier giving the number of zero after the two digits. The resulting number is the resistance in ohms.
As an example as shown in the table the first stripe is Brown for 1, the second stripe is Black for 0 the Green multiplier mean add five zeroes to 10 therefore this resistance value is 10 x 105 or 1,000,000 Ω or equivalent to 1MΩ
If the thirds stripe is black means “do not add any zero to first two figures so if the color is Brown, Black and Black stripes the resistance value would be 10Ω.
Resistors under 10 Ω have third stripe of gold or silver which are fractional decimal multiplier for instance if the stripes of the resistor are yellow, violet and gold multiply the first two digit by 0.1 and if the third stripe is silver multiply by 0.01, so for instance if the stripe of the resistor are yellow, violet and gold the resistance would be 47 X 0.1 or 4.7Ω if the third stripe is silver the resistance would be 47 X 0.01 or 0.47Ω.
Gold and silver are fractional multipliers only in the third stripe. However gold and silver are most often used as fourth stripe to indicate how accurate the resistance value is.
The amount by which the actual resistance can be different from the color coded value is the tolerance, usually given in percent. For instance, a 100,000Ω or 100KΩ resistor with ±10 percent tolerance can have a resistance 10 percent above or below its indicated resistance so when check from multi-meter the reading could range from 90,000Ω up to 110,000Ω value. The inexact value of carbon-resistors is a disadvantage resulting from their economical construction, but in most circuits 5 to 10 percent variation in resistance can be tolerated.
|Table of Standard EIA Resistor Value
(Electronic Industries Association)
|E6 (±20%)||E12 (±10%)||E24 (±5%)||E48 (±2%)||E96 (±1%)||E192 (±0.5)||E6 (±20%)||E12 (±10%||E24 (±5%)||E48 (±2%)||E96 (±1%)||E192 (±0.5)|
|Wire Number||British Wire Gauge (SWG)||American Wire Gauge (SWG)|
|Gauge No.||Inches||Equivalent in mm||Inches||Equivalent in mm||Ohms per 1000 ft. of copper wire at 25C|
STANDARD WIRE GAGE SIZES
The table shows a list of standard wire sizes in the system known as the American Wire Gauge (AWG). The gage numbers specify the size of round wire in terms of its diameter and cross-sectional circular area.
1. As the gage number increases from 1 upward, the diameter and circular area decreases. Higher gage numbers indicate thinner wire sizes.
2. The circular area doubles for every three gage sizes. For example, gage number 10 wire has an approximately twice the area of gage no. 13 wire.
3. The higher the gage number and the thinner the wire, the greater the resistance of the wire for any given length.
The cross sectional area of a round wire is measured in circular mils. A mil is a one-thousand of an inch, or 0.001 in. One circular mil is the cross-sectional area of a wire with a diameter of 1 mil. The number of circular mils in any circular area is equal to the square of the diameter in mils.
TYPES OF WIRE CONDUCTORS
Most of wire conductors are copper, but sometimes silver and aluminum are also used, copper is tinned with a thin coating of solder, which gives a silvery appearance, the wire can be solid or stranded. Stranded wire is more flexible and less likely to break open. Sizes for stranded wire are equivalent to the sum of the areas for the individual strands. For instance, two strands of no. 30 wire are equivalent to no. 27 solid wire.
A Capacitor is a passive two-terminal electrical device consisting of two or more conducting plates separated from one another by insulating material and used for storing an electric charge, capacitors are originally known as a condenser. Aside from storing energy, a capacitor can also block the flow of direct current and permit the flow of alternating current and it can work to smooth out voltage fluctuations.
Electrical energy is stored in the capacitor between the conducting plates, with the external circuitry serving as the control mechanism for releasing the energy at the predetermined rate and time. Whatever the physical construction of the device, the amount of electric charge in coulombs (q) on the capacitor is directly proportional to the potential difference in volts (V) between plates.
Capacitance (C) is the ability to store electrical charge, either with static electricity or by an electric current exhibits capacitance. Thus Capacitance is the measure of electric charge that can be stored per unit of voltage differential between the metallic conductors. The capacitance of a capacitor also depends on the size of the plates, their closeness together, and the nature of the material between them. In other words, it is directly proportional to the area of the plates and inversely proportional to the spacing between the two plates.
The unit of the capacitance is the “Farad” but because it is too large a unit for practical work, the MicroFarad (uF, one millionth of a Farad) and the Picofarad (pF, one millionth of a microfarad) are used. The higher the value, the more electrons the capacitor can store at any one time.
SOME APPLICATION OF A CAPACITOR:
BLOCKING DC VOLTAGES – The passage of direct current can be blocked by capacitor. When this happen, a circuit designer can isolate a circuit element from a dc supply. In this application, there is a choice of dielectric, each of which will allow a certain amount of leakage current caused by a random passage of electrons through or around the dielectric.
COUPLING AND DECOUPLING – capacitor block direct current and they also seem to pass alternating current. Capacitor is charged and then discharged of current as the AC voltage alternates from one section of the circuit to another or different circuits.
BYPASSING – As both blocking and coupling functions are simultaneously done, a capacitor can separate the dc and ac components of a mixed signal. To do a bypass function, the capacitor is put in parallel with the circuit element to assure that the dc portion does not appear on the circuit element.
FREQUENCY DISCRIMINATION – the capacitor in this function is, as in coupling function, employed to discriminate between signals. It should be recalled that the higher the capacitors capacitance value, the greater the current will be at any given frequency and that for a given capacitance, the higher the frequency, the more the frequency, the more current will be passed.
TIMING – The rate of charge that flows in and out of a capacitor is directly related to the capacitance (C) and the series of resistance (R) of the circuit. Thus, the selected R and C combination, otherwise known as time constant, determines the timing or speed of response of a circuit. On application can be seen in the time-delay relay.
SMOOTHING OUT VOLTAGES – Considering that unregulated power supplies are subject to transient peak and voltage surges (which can be damaging to the circuit components), capacitors are equipped with the ability to absorb these said peaks and pass on a steady voltage to a circuit. It is widely used to clean up voltage.
ENERGY STORAGE – capacitors can also be used to accumulate electrical energy from a low energy source over a long period of time. This is done by discharging the stored energy rapidly, allowing high current to perform tasks such as heating, welding or firing photoflash bulbs.
ARC SUPPRESSION – To reduce or eliminate interference caused by the rapid opening or closing of circuits (switches and relays), capacitor-resistor and capacitor-inductor combinations are used. Such arching resulting from interrupting the current flow by such circuit radiate signal in the form of noise which can interfere with any broadcast reception. The capacitor can also prolong the life of the contacts of the switches and relays.
CAPACITOR WORKING VOLTAGE:
The working voltage or WV of a capacitor, is the maximum voltage that a capacitor can withstand before the dielectric layers in the component become damaged. At higher voltages, the current may simply arc between the plates. If a capacitor is inserted in a circuit with a higher input voltage than the indicated working voltage of the capacitor a spark may develop within the capacitor and punches through the dielectric material, leaving the component useless or shorted. As always it is a good idea to select a capacitor with a working voltage greater than the voltage in the circuit for safety.
TYPES OF CAPACITOR
he plate material in a ceramic capacitor is a silver compound that is fixed or deposited upon the surface of a dielectric. The dielectric is a ceramic form made of tantanium dioxide or a silicate compound which can be of disk or tabular shape. The overall capacitor assembly is coated with plastic material. Ceramic capacitor have a high dielectric constant that provides them with high working voltage ratings. That capacitance of these capacitors varies from 1 pF to 0.1 uF. They have a wider applications like filtering, coupling and decoupling, resonant circuit parameter and others.
PAPER CAPACITOR – It’s plates are made of aluminum or tin foil with a dielectric of paper that is impregnated (saturated) with an oil or wax compound. Such capacitors are non-polarized devices. Their capacitance range from 0.001 to 1 uf and their temperature coefficient is comparatively higher than those of the other types.
PLASTIC FILM CAPACITOR :These capacitors are manufactured from plastic films usually of the oriented crystalline type. The plastics used are thermoplastic films that have been extruded, stretched and heat treated. Moister has a little effect on the plastic films dielectric properties. This fact makes make the packaging of plastic film capacitors easier compared with other types. The electrical characteristics of these capacitors relate to the manufacturing process. There are 3 general classes of plastic film capacitors – polystyrene, polyester, and polycarbonates.
MICA CAPACITOR –several strips of metal foil, either aluminum, tin or copper, are sandwiched between thin sheets of mica which serve as the dielectric materials. Alternate strips of foil are connected to form the plate. These capacitors are found in the range of 1pF to 0.01 uF in capacitance and have a stable temperature coefficient characteristic. Its useful applications are in high frequency circuit.
ELECTROLYTIC CAPACITOR – These are capacitors whose dielectric layers are formed by an electrolytic method, and need not contain an electrolyte. The most common electrolytic capacitors are the aluminum electrolytic capacitors and tantalum electrolytic capacitors.
ALUMINUM ELECTROLYTIC CAPACITORS: consist of etched foils ( the anode and cathode foils) and paper separators rolled into a tabular form. During the assembly process, thin coating of aluminum oxide is deposited upon the surface of the anode foil and this coating becomes the dielectric material of the capacitor. The thickness of the oxide determines the working voltage rate of the capacitor which generally does not exceed 500volts.
TANTALUM ELECTROLYTIC CAPACITORS: Tantalum Capacitoruse tantalum metal foils and acid electrolytes. The oxide coating deposited upon the surface of their foils has greater dielectric constant than that of aluminum oxide. These capacitors are more rugged and have high temperature coefficient. However, their working voltage ratings are much lower compared with the first. Take note that both types of electrolytic are polarized devices that must be operated under Direct Current (DC) voltage condition. Their application ranges from consumer to entertainment.
VARIABLE CAPACITOR: This capacitor are also known as air dielectric variable (or tuning) capacitor. It consists of stationary plates (stator) and a set of a position that allows them to mesh with each other without touching. By rotating the shaft of this capacitor, the surface area directly opposite the stator plates varies, causing the capacitance to vary.
In many circuit applications, resistance must be inserted into the circuit in the purpose of reducing the current or to produce a desired IR voltage drop. The component used for this are resistor and labeled with the letter R in the circuit diagrams. Resistor are the most commonly found component in all electronic equipment, from a small AM radio to a color television receiver. The common type of resistor is the carbon resistor as shown in the image.
TYPE OF RESISTORS:
The two main characteristics of a resistor are its R in ohms and the wattage rating. Resistors available values ranges from a fraction of an ohms up to many mega ohms. The power rating can be as high as several watts or as low as 1/10 W.
The power rating of a resistor is important because it specifies the maximum wattage the resistor can dissipate without producing excessive heat that can damage the component and or other components in the circuit. Dissipation means that the power is wasted as I2R loss. Since the result heat is not used, the generated heat which is usually too much can make the resistor burn open.
When power dissipation is about 5 watts or more wirewound resistors are used, specially in devices that require high current handling capability, heat dissipation and resistance stability and accuracy. For 2W or less, carbon resistor are preferable because they are smaller and cost less.
Carbon resistors are most common in electronic equipment because they are smaller and cost less as compared to wirewound resistor, Usually higher R values have smaller wattage because they have less current.
Both carbon and wirewound resistors can be either fixed or variable. A fixed resistor have a specific R that cannot be adjusted, while a variable resistor can be adjusted for any value between zero ohms up to its maximum R value.
Carbon composition variable resistors are commonly used for control, such as the volume control in a radio receiver or the contrast control in a television receiver. An application for a variable resistor is to divide the voltage from a power supply.
1. WIREWOUND RESISTOR: Resistance wire such as manganin wrapped around an insulating core, Commonly used insulating materials are cement, porcelain, or just plain compressed paper.
The wire is bare, but usually the entire unit is encased in an insulator. The length of wire used and its specific resistivity determine the resistance of the unit.
Wirewound ResistorSince wirewound resistors are generally for low-resistance high-power applications, wirewound resistors are available in power ratings from 5W to several hundred watts, with resistance range of less than 1Ω to several thousand ohms. In addition, wirewound precision resistors are used where accurate, stable resistance values are require.
2. CARBON COMPOSITION RESISTOR: This type of resistor are made of finely divided carbon or graphite mixed with a powdered insulating material in the proportions needed for the desired value. The resistor element is usually enclosed in a plastic case for insulation and mechanical strength.
Joined to the two end of the carbon resistance elements are metal caps with leads of tinned copper wire for soldering the resistor connections into a circuits. Carbon resistors are commonly available in resistance values of 1/10, 1/8, ¼, ½, 1 or 2 watts.
3. CARBON FILM RESISTOR: Carbon film resistors are manufactured by depositing a carbon film on a ceramic substrate. In many ways semilar to carbon composition resistors, they can be interchange with each other, the cost is less than for the hot-molded carbon-composition type.
4. METAL-FILM RESISTORS: These are form by means of vacuum deposition, a process by which any of the number of different metal or metal oxide films are deposited on a suitable insulating mandrel or core.
Nickel and chromium are deposited on the alumina ceramic core and the unit is then subjected to laser trimming. Metal film resistors are laser trimmed or helixed to obtain the desired resistance value before the protective insulation coat is applied.
TYPES OF METAL FILMS RESISTORS
- METAL-OXIDE DEPOSITION — This process makes use of a chemical vapor deposite to a tin-oxide film onto a glass substrate. Although this tin oxide resistor is similar in performance to evaporated or sputtered metal film, the technique is obviously not capable of achieving the level of precision possible with other thin-film process.
- BULK METAL. — This process produces a flat instead of cylindrical elements. It is an expensive process but produces resistor with a tight tolerance and excellent temperature coefficient of resistance characteristics, used exclusively for ultra-precision applications. This process entails the laminations of metal foil to a substrate and later etched chemically to produce a serpentine rather than helical conduction path.
- THICK FILM — This process coats ceramic substrate with a glass-metal matrix material. Later, it is fired at an extremely high temperature to produce a metallic film. Unlike in other processes wherein the resistive elements are subjected to a very temperature in order to vaporize materials, the thick film process does it to cure.
- VACUUM DEPOSITION — Also known as evaporated metal film, it is the original metal film resistor manufacturing process. This techniques superheats a nickel chromium alloy wire by resistance or electron — beam heating in a vacuum. As the alloy evaporizes, it is deposited on ceramic substrates which are then loaded into a vacuum container. To achieve the resistance ranges, manufacturers make use of contaminants called dopants.
- SPUTTERING — This is a more recently developed techniques and closely related to vacuum deposition. It is likewise yields a product consisting of nichrome resistor on a ceramic substrate.5. CERMIT-FILM RESISTORS: These have a carbon coating fired onto a solid ceramic substrate. The purpose is to have a exact or precise R values and greater stability with heat. They are often made in a small square, with leads to fit a PC board. A flat package with multiple leads can be used for several resistors in one unit.
- VARIABLE RESISTORS:
Variable resistors can be wirewound or a carbon type. Inside the metal case, the control has a circular disk that is the carbon-composition resistance element. Joined to the two end are the outside soldering-lug terminals 1 and 3. The middle lug 2 is connected to the variable arm contacting the resistor element by a metal spring wiper. As the shaft of the control is rotated, the variable arm moves the wiper to make contact at different points.
When the contact moves closer to one end, the resistance decreases between this end and the variable arm. The variable resistance is zero when the wiper contacts this end but is maximum with the variable arm at the opposite end. Between the two outside ends, the resistance is not variable but always has the maximum resistance of the control.
RESISTORS COLOR CODING :
In addition to having the required resistance value in ohms, a resistor should have a wattage rating high enough to dissipate the I2R power produced by the current flowing through the resistance, without becoming too hot. If a resistor becomes too hot because of excessive power dissipation, it can change appreciably in resistance value or burn.
The power rating is a physical property depending on the resistor construction, specifically physical size.
1. The larger the physical size of the resistor indicates a higher power rating.
2. Higher-wattage resistors can operate at higher temperature.
3. Wirewound resistors are physically larger with higher wattage rating than carbon resistor.
For both types, a higher power rating allows a higher voltage rating. The rating gives the highest voltage that may be applied across the resistor without internal arching. In wirewound resistors, excessive voltage can produce an arc between turns; in carbon resistors, the arc is between carbon granules.
SERIES AND PARALLEL COMBINATION:
In some cases two or more resistors are combines in series or parallel to obtain a desired resistance value with a higher wattage rating as shown.
series parallel resistors
The total resistance depend on the series and parallel connections. However, the combination has a power rating equal to the sum of the individual wattage ratings, whether the resistors are in parallel or series. The reason is that the total physical size increases with each added resistor, Such combinations can be used to obtain a higher power rating.
Figure a, the two equal resistors in series double the resistance. Also the power rating of the combination is twice the value for one resistor.Figure b, the two equal resistor in parallel have one-half the resistance. However the combined power rating is still twice the value for one resistor.
Figure c, the series parallel combination of four resistors makes RT the same on each resistor. However, the total power rating is four times the value for one resistor.
CHECKING RESISTOR WITH OHMMETER :
An open resistor reads infinitely high ohms. For some reason, infinite ohms is often confused with zero ohms. Remember though that infinite ohms means an open circuit. The current is zero but the resistance is infinitely high. Furthermore, it is practically impossible for a resistor to become short-circuited in itself. The resistor may be short circuited by some other part of the circuit, however, the construction of resistors is such that the trouble they develop is an open circuit, with infinitely high resistance in ohms.
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