Thursday, December 16, 2010

TV and electronics repair in Edmonds Washington

We specialize in LCD TV and monitor repair


Monday-Friday 10:00AM-6:00PM

Fast and Affordable In Home Service

Television and electronics repair specialists. We also do computer upgrades and repair video game consoles or arcade games. Our technicians can repair many devices other "electronic repair specialists" won't even look at. Preher-Tech repairs most brands and types of TVs and monitors including Plasma, LCD ,DLP and LED. Call today and make an appointment.

Now serving Seattle and the surrounding areas including Seatac, Tacoma, Federal Way, Kent, Bellevue, Renton, Everett, Edmonds, Lynnwood, Kirkland, Bothell, Mill Creek and more.

Payment Types Accepted:
Cash, Check, MasterCard, Visa, PayPal

Visit our website,

TV and electronics repair in Seattle Washington


We specialize in LCD TV and monitor repair


Monday-Friday 10:00AM-6:00PM

Fast and Affordable In Home Service

Television and electronics repair specialists. We also do computer upgrades and repair video game consoles or arcade games. Our technicians can repair many devices other "electronic repair specialists" won't even look at. Preher-Tech repairs most brands and types of TVs and monitors including Plasma, LCD ,DLP and LED. Call today and make an appointment.

Now serving Seattle and the surrounding areas including Seatac, Tacoma, Federal Way, Kent, Bellevue, Renton, Everett, Edmonds, Lynnwood, Kirkland, Bothell, Mill Creek and more.

Payment Types Accepted:
Cash, Check, MasterCard, Visa, PayPal
Visit our website,

Wednesday, December 8, 2010

Dip meter

Grid dip oscillator (GDO), also called grid dip meter, dip meter, dipmeter, or just dipper, is a measuring instrument to measure resonant frequency of radio frequency circuits. It measures the amount of absorption of a high frequency inductively coupled magnetic field by nearby objects. It is an oscillator whose output energy changes in the vicinity of a resonant circuit which is tuned to the frequency the oscillator generates; somewhat similar to an acoustic tone becoming louder when generated in the vicinity of a resonant cavity or a string tuned to the same frequency. At the heart of the instrument is a tunable LC circuit with a coil that serves as a loose inductive coupling to the measured LC resonant circuit. Resonance is indicated by a dip in the meter indicator on the device, usually based on a microammeter.
To read more click here.
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Electrical impedance

Electrical impedance, or simply impedance, describes a measure of opposition to alternating current (AC). Electrical impedance extends the concept of resistance to AC circuits, describing not only the relative amplitudes of the voltage and current, but also the relative phases. When the circuit is driven with direct current (DC) there is no distinction between impedance and resistance; the latter can be thought of as impedance with zero phase angle.

The symbol for impedance is usually and it may be represented by writing its magnitude and phase in the form . However, complex number representation is more powerful for circuit analysis purposes. The term impedance was coined by Oliver Heaviside in July 1886.[1][2] Arthur Kennelly was the first to represent impedance with complex numbers in 1893.[3]

Impedance is defined as the frequency domain ratio of the voltage to the current[citation needed]. In other words, it is the voltage–current ratio for a single complex exponential at a particular frequency ω. In general, impedance will be a complex number, with the same units as resistance, for which the SI unit is the ohm. For a sinusoidal current or voltage input, the polar form of the complex impedance relates the amplitude and phase of the voltage and current. In particular,

The magnitude of the complex impedance is the ratio of the voltage amplitude to the current amplitude.
The phase of the complex impedance is the phase shift by which the current is ahead of the voltage.
The reciprocal of impedance is admittance (i.e., admittance is the current-to-voltage ratio, and it conventionally carries units of siemens, formerly called mhos).

Read more by clicking here.

Electrical reactance

Reactance is the opposition of a circuit element to a change of current, caused by the build-up of electric or magnetic fields in the element. Those fields act to produce counter-emf that is proportional to either the rate of change (time derivative), or accumulation (time integral), of the current. An ideal resistor has zero reactance, while ideal inductors and capacitors consist entirely of reactance, with neither series resistance nor parallel conductance.

Read more by clicking here.

Wednesday, December 1, 2010

Boost converter

A boost converter (step-up converter) is a power converter with an output DC voltage greater than its input DC voltage. It is a class of switching-mode power supply (SMPS) containing at least two semiconductor switches (a diode and a transistor) and at least one energy storage element. Filters made of capacitors (sometimes in combination with inductors) are normally added to the output of the converter to reduce output voltage ripple.

Read more by clicking here


Buck converter

A buck converter is a step-down DC to DC converter. Its design is similar to the step-up boost converter, and like the boost converter it is a switched-mode power supply that uses two switches (a transistor and a diode), an inductor and a capacitor.

The simplest way to reduce a DC voltage is to use a voltage divider circuit, but voltage dividers waste energy, since they operate by bleeding off excess power as heat; also, output voltage isn't regulated (varies with input voltage). Buck converters, on the other hand, can be remarkably efficient (easily up to 95% for integrated circuits) and self-regulating, making them useful for tasks such as converting the 12–24 V typical battery voltage in a laptop down to the few volts needed by the processor.

Read more by clicking here


Monday, November 29, 2010

Electret microphone

An electret microphone is a type of condenser microphone, which eliminates the need for a polarizing power supply by using a permanently-charged material.

An electret is a stable dielectric material with a permanently-embedded static electric charge (which, due to the high resistance and chemical stability of the material, will not decay for hundreds of years). The name comes from electrostatic and magnet; drawing analogy to the formation of a magnet by alignment of magnetic domains in a piece of iron. Electrets are commonly made by first melting a suitable dielectric material such as a plastic or wax that contains polar molecules, and then allowing it to re-solidify in a powerful electrostatic field. The polar molecules of the dielectric align themselves to the direction of the electrostatic field, producing a permanent electrostatic "bias". Modern electret microphones use PTFE plastic, either in film or solute form, to form the electret.
Read more by clicking here


Electret (formed of elektr- from "electricity" and -et from "magnet") is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet. Oliver Heaviside coined this term in 1885. Materials with electret properties were, however, already studied since the early 18th century. One particular example is the electrophorus, a device consisting of a slab with electret properties and a separate metal plate. The electrophorus was originally invented by Johan Carl Wilcke in Sweden and again by Alessandro Volta in Italy.

Read more at wikipedia by clicking here

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A loudspeaker (or "speaker") is an electroacoustic transducer that converts an electrical signal into sound. The speaker moves in accordance with the variations of an electrical signal and causes sound waves to propagate through a medium such as air or water.

After the acoustics of the listening space, loudspeakers (and other electroacoustic transducers) are the most variable elements in a modern audio system and are usually responsible for most distortion and audible differences when comparing sound systems.

Driver design:
The most common type of driver uses a lightweight diaphragm, or cone, connected to a rigid basket, or frame, via a flexible suspension that constrains a coil of fine wire to move axially through a cylindrical magnetic gap. When an electrical signal is applied to the voice coil, a magnetic field is created by the electric current in the voice coil, making it a variable electromagnet. The coil and the driver's magnetic system interact, generating a mechanical force that causes the coil (and thus, the attached cone) to move back and forth, thereby reproducing sound under the control of the applied electrical signal coming from the amplifier. The following is a description of the individual components of this type of loudspeaker.

Read more at wikipedia by clicking here
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Tuesday, November 23, 2010


A multivibrator is an electronic circuit used to implement a variety of simple two-state systems such as oscillators, timers and flip-flops. It is characterized by two amplifying devices (transistors, electron tubes or other devices) cross-coupled by resistors and capacitors.

There are three types of multivibrator circuit:

astable, in which the circuit is not stable in either state—it continuously oscillates from one state to the other. Due to this, it does not require an input (Clock pulse or other).
monostable, in which one of the states is stable, but the other is not—the circuit will flip into the unstable state for a determined period, but will eventually return to the stable state. Such a circuit is useful for creating a timing period of fixed duration in response to some external event. This circuit is also known as a one shot. A common application is in eliminating switch bounce.
bistable, in which the circuit will remain in either state indefinitely. The circuit can be flipped from one state to the other by an external event or trigger. Such a circuit is important as the fundamental building block of a register or memory device. This circuit is also known as a latch or a flip-flop.
In its simplest form the multivibrator circuit consists of two cross-coupled transistors. Using resistor-capacitor networks within the circuit to define the time periods of the unstable states, the various types may be implemented. Multivibrators find applications in a variety of systems where square waves or timed intervals are required. Simple circuits tend to be inaccurate since many factors affect their timing, so they are rarely used where very high precision is required.

Before the advent of low-cost integrated circuits, chains of multivibrators found use as frequency dividers. A free-running multivibrator with a frequency of one-half to one-tenth of the reference frequency would accurately lock to the reference frequency. This technique was used in early electronic organs, to keep notes of different octaves accurately in tune. Other applications included early television systems, where the various line and frame frequencies were kept synchronized by pulses included in the video signal.

Read more about multivibrators at wikipedia by clicking here

Click here for another great article on multivibrators

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Tuesday, November 16, 2010

Logic Gates

A logic gate performs a logical operation on one or more logic inputs and produces a single logic output. The logic is called Boolean logic and is most commonly found in digital circuits. Logic gates are primarily implemented electronically using diodes or transistors, but can also be constructed using electromagnetic relays (relay logic), fluidic logic, pneumatic logic, optics, molecules, or even mechanical elements.
Click here to read more from the Wikipedia
Click here to download a PDF that covers basic logic gates and there operation.
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Tuesday, November 9, 2010

Operational Amplifiers

An Operational amplifier ("op-amp") is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. An op-amp produces an output voltage that is typically hundreds of thousands times larger than the voltage difference between its input terminals.
Operational amplifiers are important building blocks for a wide range of electronic circuits. They had their origins in analog computers where they were used in many linear, non-linear and frequency-dependent circuits. Their popularity in circuit design largely stems from the fact that the characteristics of the final elements (such as their gain) are set by external components with little dependence on temperature changes and manufacturing variations in the op-amp itself.

If you are interested in reading more about op-amps I suggest downloading this 464 page PDF from Texas Instruments, "Op Amps For Everyone" , click here to download.
You can also purchase the most current version of "Op Amps For Everyone" by clicking on the picture below.

For basic information on op-amps click here and here
More books on op-amps:

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Dave Jones and the EEVblog

If you don't know who Dave Jones is I urge you to go check out his website and his YouTube page as well
I think Dave's videos are some of the best on YouTube in my opinion, I find myself constantly checking to see when he has added a new one. Guaranteed to make you laugh and even teach you something as well, not to mention Dave's awesome product reviews.
Don't forget to visit as well

Monday, November 8, 2010

Electronics Certification

If you are interested in getting certified in the field of electronics these are a couple of my suggested places to get certified and in my opinion are far more current than other certification institutes like the ISCET for instance which is extremely outdated.

Expert Rating-
ExpertRating believes in delivering cutting edge competency evaluation and skills training services based on scientific testing and training methodologies through a quality driven approach. ExpertRating strives to continually improve and upgrade its services by adopting the latest technologies and methodologies in the development and delivery of testing and training services. Expert Rating has highly recognized electronics certifications. The test fees are extremely reasonable, but you must retest every year.

Click here to see all the electronics certificates that Expert Rating has to offer.

CETG(Consumer Electronics Technicians Group)-
The CETG is a group of technicians and electronics service professionals that have come together to help set a standard for knowledge and skill levels that need to be met by today's cosumer electronics repair men and women. We provide certification for both students and profesional technicians. Our certification let's employers and or customers know that you have completed the necessary steps to becoming a serious , knowledgeable technician that has an extensive undertanding of electronics and the skills to complete any electronics repair job properly and safely.

The CETG offfers three levels of certification:



Master Technician

Upon certification you will recieve a certificate and wallet card valid for five years.

Remeber to visit for electronics repair and design information.

Saturday, November 6, 2010

Make Your Own Ring Tester

In this post I will share with you all the info you will need to make a homemade ring tester also called a FBT/LOPT tester, note FBT= Fly Back Transformer, LOPT= Line Output Transformer.
Although originally designed to test flyback transformers this tool is used more often today for checking the primary coil of SMPS transformers for shorted windings and also the primary and secondary windings of high voltage transformers found in inverter circuits along with many other high Q inductive components and of course I still check the occasional flyback which itself is a high voltage switching transformer.

Click here for the assembly manual for the original dick smith ring tester which is no longer in production. This manual includes a schematic and a parts list.
Below are some pictures of the beautiful ring tester my good friend Behzad made using the schematic and parts list from the included assembly manual.

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Tuesday, November 2, 2010

Monday, November 1, 2010

Testing Semiconductors

Click here to go to Samuel M. Goldwasser's webpage "Basic Testing of Semiconductor Devices" and learn his listed methods for testing diodes, transistors, darlington transistors, TRIACs, DIACs, digital transistors, SCRs and more.

Also come visit for all kinds of electronics information.


TRIAC, from Triode for Alternating Current, is a genericized tradename for an electronic component which can conduct current in either direction when it is triggered (turned on), and is formaly named as bidirectional triode thyristor or bilateral triode thyristor.

A TRIAC is approximately equivalent to two complementary unilateral thyristors (one is anode triggered and another is cathode triggered SCR) joined in inverse parallel (paralleled but with the polarity reversed) and with their gates connected together. It can be triggered by either a positive or a negative voltage being applied to its gate electrode (with respect to A1, otherwise known as MT1). Once triggered, the device continues to conduct until the current through it drops below a certain threshold value, the holding current, such as at the end of a half-cycle of alternating current (AC) mains power. This makes the TRIAC a very convenient switch for AC circuits, allowing the control of very large power flows with milliampere-scale control currents. In addition, applying a trigger pulse at a controllable point in an AC cycle allows one to control the percentage of current that flows through the TRIAC to the load.

Click here to read more about TRIACs

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The DIAC, or 'diode for alternating current', is a trigger diode that conducts current only after its breakdown voltage has been reached momentarily.

When this occurs, diode enters the region of negative dynamic resistance, leading to a decrease in the voltage drop across the diode and, usually, a sharp increase in current through the diode. The diode remains "in conduction" until the current through it drops below a value characteristic for the device, called the holding current. Below this value, the diode switches back to its high-resistance (non-conducting) state. This behavior is bidirectional, meaning typically the same for both directions of current.

Most DIACs have a three-layer structure with breakdown voltage around 30 V. In this way, their behavior is somewhat similar to (but much more precisely controlled and taking place at lower voltages than) a neon lamp.

DIACs have no gate electrode, unlike some other thyristors that they are commonly used to trigger, such as TRIACs. Some TRIACs contain a built-in DIAC in series with the TRIAC's "gate" terminal for this purpose.

DIACs are also called symmetrical trigger diodes due to the symmetry of their characteristic curve. Because DIACs are bidirectional devices, their terminals are not labeled as anode and cathode but as A1 and A2 or MT1 ("Main Terminal") and MT2.

Click here to read more about DIACs

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Saturday, October 30, 2010

Radio Fundamentals PDF Download

If you are interested in learning the basics of radio wave propagation, transmission lines and antennas here is a great PDF file for you to download. "COMMUNICATIONS-ELECTRONICS FUNDAMENTALS" This 269 PDF from the headquarters department of the army is a great way to get started in learning about the basics of radio.

Click here to download.

If you have trouble with the link email me and I will email you a copy.

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Thursday, October 21, 2010

Amateur Radio

Amateur radio also called ham radio is an awesome hobby and lots of fun. If you are already into electronics and enjoy studying radio theory than this is most likely a hobby you would really enjoy. Preher-Tech has added an amateur radio page to our website that includes basic info on amateur radio as well as a list of all the books you will need to get started in this hobby. I myself am a general class operator, my call sign is KF7LTV
and I am planning to go get my amateur extra license very soon, giving me full privileges on the amateur bands. Hope to hear some of you on the air soon. Click here to visit our amateur radio page.

Don't forget to visit for all your electronics needs.

Tools and Test Equipment

Well per the request of many viewers and newsletter subscribers and many random emails we finally decided to add a sales page to our website featuring all our favorite tools and test equipment including digital multimeters, analog multimeters, tool kits, soldering stations, SMD rework stations, oscilloscopes, LCR and ESR meters and more. We are looking for suggestions as well so tell us what you want to see on the page and we will do our best to make it happen. Thanks to everyone for all your support over the years and we look forward to servicing you into the future.

Cick here to visit our new "Toools and Test Equipment" page

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Tuesday, October 19, 2010

Electrolytic capacitors

An electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic conducting liquid, as one of its plates, to achieve a larger capacitance per unit volume than other types. They are often referred to in electronics usage simply as "electrolytics". They are used in relatively high-current and low-frequency electrical circuits, particularly in power supply filters, where they store charge needed to moderate output voltage and current fluctuations in rectifier output. They are also widely used as coupling capacitors in circuits where AC should be conducted but DC should not. There are two types of electrolytics; aluminum and tantalum.

Electrolytic capacitors are capable of providing the highest capacitance values of any type of capacitor. However they have drawbacks which limit their use. The voltage applied to them must be polarized; one specified terminal must always have positive potential with respect to the other. Therefore they cannot be used with AC signals without a DC bias. They also have very low breakdown voltage, higher leakage current and inductance, poorer tolerances and temperature range, and shorter lifetimes compared to other types of capacitors.
Read the full article by clicking here.
Don't forget to visit for electronics repair and design information. You may especially want to check out our tools and tips page by clicking here.

Switching-Mode Power Supply Design

I found this wonderful site with lots of tutorials on SMPS design and you can also join their news letter to get great SMPS design information sent to your inbox.
Click here to see this great website.
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Opto-isolator Tester

One of my newsletter subscribers sent me a picture of the preher-tech opto-isolator tester which he had built from the parts list and schematic I had included in my article on testing opto-isolators. He did such a great job even etching a PCB that I had to share the pictures of his work with all of you. Great job Beh!
Note: Beh switched the LEDs so red indicates power on and green indicates a good opto-isolator.
If anyone else has pictures of there opto-isolator tester built from my design please send it to me and I will post it here to share with everyone. Email pictures to
Also if you missed the article on testing opto-isolators you can download it by clicking here.
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Sunday, October 17, 2010

Laptop repair guide

•Do you want to learn how to fix laptops?

•Are you afraid to work on laptops for fear of breaking them?

•Do you want to expand your skill set so you can make big money fixing laptops instead of sending the business away?

•Receive the same high level of Podnutz quality, as Steve releases the long awaited Laptop Repair Video Collection!

What do you get in this package? You'll see in full 960x540 HD video:

•How to replace a motherboard
•How to replace an LCD Screen
•What to do when the laptop keeps shutting down
•How to fix DC power jacks
•The crucial difference between a bad screen and a bad inverter board
•How to replace hinges
•Where I buy all my parts
•The best way to go about taking a laptop apart
•How to solder
•The art of fixing AC adapters
•How to handle a laptop that has had liquid spilled in it
•what to do when a laptop overheats
•how to replace CD/DVD drives, RAM, processors, hard Drives and wireless cards
•and much, much more!!

Click here to go to the sale page and learn more about the "Laptop Repair Video Collection" including customer testimonies.

Tuesday, October 12, 2010

Learn basic electronics and electrical engineering

Take a look at this new guide by Greg Carpenter, "Introduction To Basic Electronics". This guide will get you started with all the basics of electronics the easy fun way, at home and at your own pace.

Click here to learn more about this great guide "Introduction To Basic Electronics" and get started learning about electronics today.

Don't forget to visit and also if you ever have any electronics related questions remember you can always email me

How to repair LCD TVs

Are you looking for a guide to show you how to fix LCD TVs? If so then you may want to take a look at "Troubleshooting and Repairing LCD TVs". Whether you are a technician that is looking to expand your repair skills or just someone who has a broken TV that wants to repair it at home and avoid repair costs or replacing your TV than this is the book for you. 195 pages and only $25.00 and this ebook even comes with email support from the author John Preher. So don't hesitate to grab this guide today and start fixing LCD TVs.

You may also be interested in "LCD TV Repair Case Histories" if you are looking for a quick fix for your LCD TV. Click here to learn more about "LCD TV Repair Case Histories".

Wednesday, October 6, 2010

ShopJimmy UK

We are pleased to announce that ShopJimmy has fully launched their UK website.

That's right!! The same smiley face in a brand new place.

To visit ShopJimmy UK click here.

Tuesday, October 5, 2010

Understanding and testing opto-isolators

An opto-isolator also called an opto-coupler or photo-coupler allows a signal to pass from one circuit to another but allows the two circuits to remain electrically isolated. The most common opto-isolator which comes in IC package consists of an LED which shines onto the base of a photo-transistor (usually an npn transistor) and allows current to flow from collector to emitter until the LED is turned off. When a signal is applied to the LED it then shines light that is varied in brightness with the same amplitude as the input signal, this light lands upon the photo-transistor (the resistance of the collector/emitter junction now changes with the varying light) which passes the signal onto the next circuit.

Basic opto-isolator symbol.
If you do a lot of work on switch mode power supplies than you have surely seen the opto-isolators used in the feed back section of the power supply.

Opto-isolators in LCD TV SMPS.

If you want to read more about opto-isolators including my 3 methods for testing them than dowload my free article "Understanding and Testing Opto-isolators" by clicking here.

Included in the article is a schematic and parts list for a simple opto-isolator tester.

Don't forget to visit and also if you have any electronics related questions you can email me for assistance.

Recommended Repair Guides:

LCD TV Repair Guide

LCD TV Repair Case Histories

Thursday, September 23, 2010

Electronics Repair Articles

Well, Jestine Yong has done it again. His fifth e-book is now available, "My Best Collection of Electronics Repair Articles". This 215 page guide is absolutely packed with electronics repair information that will benefit every electronics technician. Click here, then in the new window click on the picture of the book to go to the info page and find out more about this awesome book.

Wednesday, September 22, 2010

Diode Types and Their Uses

There are many different types of diodes that are available for use in electronics design. Different semiconductor diode types can be used to perform different functions as a result of the properties of these different diode types.

Semiconductor diodes can be used for many applications. The basic application is obviously to rectify waveforms. This can be used within power supplies or within radio detectors. Signal diodes can also be used for many other functions within circuits where the "one way" effect of a diode may be required.

Diodes are not just used as rectifiers, as various other types of diode can be used in many other applications. Some other different types of diodes include: light emitting diodes, photo-diodes, laser diodes and more as detailed in the list below.

Many of the different types of diodes mentioned below have further pages providing in-depth information about them including their structures, method of operation, how they may be used in circuits, and precautions and tips for using them in electronics design.

Types of diodes
It is sometimes useful to summarise the different types of diodes that are available. Some of the categories may overlap, but the various definitions may help to narrow the field down and provide an overview of the different diode types that are available.

Avalanche diode: The avalanche diode by its very nature is operated in reverse bias. It uses the avalanche effect for its operation. In general the avalanche diode is used for photo-detection where the avalanche process enables high levels of sensitivity to be obtained, even if there are higher levels of associated noise.
Laser diode: This type of diode is not the same as the ordinary light emitting diode because it produces coherent light. Laser diodes are widely used in many applications from DVD and CD drives to laser light pointers for presentations. Although laser diodes are much cheaper than other forms of laser generator, they are considerably more expensive than LEDs. They also have a limited life. See related articles list in left hand margin.
Light emitting diodes: The light emitting diode or LED is one of the most popular types of diode. When forward biased with current flowing through the junction, light is produced. The diodes use component semiconductors, and can produce a variety of colours, although the original colour was red. There are also very many new LED developments that are changing the way displays can be used and manufactured. High output LEDs and OLEDs are two examples. See related articles list in left hand margin.
Photo diode: The photo-diode is used for detecting light. It is found that when light strikes a PN junction it can create electrons and holes. Typically photo-diodes are operated under reverse bias conditions where even small amounts of current flow resulting from the light can be easily detected. Photo-diodes can also be used to generate electricity. For some applications, PIN diodes work very well as photo detectors. See related articles list in left hand margin.
PIN diode: This type of diode is typified by its construction. It has the standard P type and N-type areas, but between them there is an area of Intrinsic semiconductor which has no doping. The area of the intrinsic semiconductor has the effect of increasing the area of the depletion region which can be useful for switching applications as well as for use in photo diodes, etc. See related articles list in left hand margin.
Point contact diode: This type of diode is one of the most basic forms of diode in terms of its construction but it performs in the same way as a PN junction diode. This type of diode consists of a piece of N-type semiconductor, onto which a sharp point of a specific type of metal wire (group III metal) is placed. As this physical junction is formed, some of the metal from the wire migrates into the semiconductor and produces a PN junction. Point contact diodes have a very low level of capacitance because the resulting junction is very small. As such this type of diode is ideal for many radio frequency (RF) applications. The downside of the small junction is that they cannot carry high levels of current but they have the advantage that they are very cheap to manufacture, although their performance is not particularly repeatable.
PN Junction: The standard PN junction may be thought of as the normal or standard type of diode in use today. These diodes can come as small signal types for use in radio frequency, or other low current applications which may be termed as signal diodes. Other types may be intended for high current and high voltage applications and are normally termed rectifier diodes. See related articles list in left hand margin.
Rectifier diode: This definition refers to diodes that are used in power supplies for rectifying alternating power inputs. The diodes are generally PN junction diodes, although Schottky diodes may be used if low voltage drops are needed. They are able to rectify current levels that may range from an amp upwards.
Schottky diodes: This type of diode has a lower forward voltage drop than ordinary silicon PN junction diodes. At low currents the drop may be somewhere between 0.15 and 0.4 volts as opposed to 0.6 volts for a silicon diode. To achieve this performance they are constructed in a different way to normal diodes having a metal to semiconductor contact. They are widely used as clamping diodes, in RF applications, and also for rectifier applications.
Signal diode: This for of diode is used for small signal applications where small values of current are drawn. Diodes with the description of signal diode are generally the standard PN junction diode types.
Step recovery diode: A form of microwave diode used for generating and shaping pulses at very high frequencies. These diodes rely on a very fast turn off characteristic of the diode for their operation.
Tunnel diode: Although not widely used today, the tunnel diode was used for microwave applications where its performance exceeded that of other devices of the day. See related articles list in left hand margin.
Varactor diode or varicap diode: This type of diode is used in many radio frequency (RF) applications. The diode has a reverse bias placed upon it and this varies the width of the depletion layer according to the voltage placed across the diode. In this configuration the varactor or varicap diode acts like a capacitor with the depletion region being the insulating dielectric and the capacitor plates formed by the extent of the conduction regions. The capacitance can be varied by changing the bias on the diode as this will vary the width of the depletion region which will accordingly change the capacitance. See related articles list in left hand margin.
Zener diode: The Zener diode is a very useful type of diode as it provides a stable reference voltage. As a result it is used in vast quantities. It is run under reverse bias conditions and it is found that when a certain voltage is reached it breaks down. If the current is limited through a resistor, it enables a stable voltage to be produced. This type of diode is therefore widely used to provide a reference voltage in power supplies. Two types of reverse breakdown are apparent in these diodes: Zener breakdown and Impact Ionisation. However the name Zener diode is used for the reference diodes regardless of the form of breakdown that is employed. See related articles list in left hand margin.

Read more by clicking here

You may also be interested in our LCD TV Repair Guide. Click here to read more.

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If you have any electronics repair questions email me

Saturday, September 18, 2010

Gateway 2100 repaired

I felt it was time to post another case history.

Gateway 2100 LCD monitor, the monitor would turn on screen would flicker and then go black. After opening the monitor I found 1 capacitor, 47uF @16V with an ESR of 10 ohms(obviously bad) in the secondary side of the SMPS section of the SMPS/Inverter board. Looking at the inverter section I noticed two puffed and vented electrolytic capacitors both 220uF @16V, locations C301 and C302 that were obviously bad as well. Sorry but I did not record the location of the 47uF capacitor, but you can see where all the capacitors were located in the photos. I also noticed some darkened spots on the component side of the PCB, on the other side, the solder side of the PCB you could see that where the dark spots were is where the inverter circuit MOSFETs were located, U301, U302, U304 and U305.After testing the MOSFETs for shorts between gate to drain and gate to source to my surprise they tested good, but they did have major solder connection problems, the solder on their connections had completely broken down from heat. I re-soldered all the connections and replaced all the bad electrolytic capacitors and checked for any other problems with the monitor. After putting the monitor back together hooking up signal and turning it on, it worked like new.

If you are wondering why the transistors are identified with a U instead of a Q, as normally transistors are labeled with a Q and ICs are labeled with a U, well this is the case on some PCBs the designers will label transistor locations with U instead of Q and instead of labeling ICs as U they will just print IC.

Mail in repair service:
We offer mail in repair service on LCD monitors. We do the repair on the PSU/inverter board from the monitor in this post for $40.00 plus return shipping and handling. Click here to see our mail in repair service page for more information.

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Different types of capacitors and their uses

Electronic capacitors are one of the most widely used electronic components. These electronic capacitors only allow alternating or changing signals to pass through them, and as a result they find applications in many different areas of electronic circuit design. There are a wide variety of types of capacitor including electrolytic, ceramic, tantalum, plastic, sliver mica, and many more. Each capacitor type has its own advantages and disadvantages can be used in different applications.

The choice of the correct capacitor type can have a major impact on any circuit. The differences between the different types of capacitor can mean that the circuit may not work correctly if the correct type of capacitor is not used. Accordingly a summary of the different types of capacitor is given below, and further descriptions of a variety of capacitor types can be reached through the related articles menu on the left hand side of the page below the main menu.

Capacitor construction
In essence the construction of an electronic capacitor is very simple, although in practice a lot of research and development has been put into capacitor technology. The basic electronics components consist of two plates that are insulated from one another. In between them there is an insulating medium known as the dielectric. The value of the electronic capacitor is dependent upon the area of the plates, the distance between them and the dielectric constant of the material or dielectric between them. The greater the area of the plates, the closer they are together and the greater the value of the dielectric constant the greater the value of capacitance.

Today, electronic capacitors are able to provide relatively high levels of capacitance within components that occupy a small volume. This is achieved in a number of ways. One is to have several sets of plates, and another is to place the plates very close to one another, having a thin layer of dielectric placed between them. In addition to this special insulating dielectric materials have been developed to enable high levels of capacitance to be achieved.

The method of construction of these electronic components is also important. In some capacitors the plates may be flat, and normally these capacitors will have rectangular, or more exactly cuboid shapes. Some will be tubular and in these capacitors the plates will be wound round on each other. The reasons for these types of construction are normally dependent upon the way in which the capacitors must be manufactured. The final stage in the construction of an electronic capacitor is to place it in a protective casing. In some instances it may be dipped in an insulating coating, in others it may be contained within a metal can.

Some capacitors types are what are termed polar or polarised. When this is the case the electronic capacitor has a positive and a negative connection and it must be placed in circuit so that the voltage across it is in a particular sense. If the voltage is incorrectly placed across the component then it may be damaged. Fortunately many capacitors, and in particular low value ones are non-polar and can be placed in circuit either way round.

Although there is a large variety that are available the most commonly used are ceramic, plastic film types, electrolytic and tantalum. These names refer to the type of dielectric that is used within the capacitor.

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Different types of resistors

Resistor Types:

Resistors (R), are the most commonly used of all electronic components, to the point where they are almost taken for granted. There are many different resistor types available with their principal job being to "resist" the flow of current through an electrical circuit, or to act as voltage droppers or voltage dividers. They are "Passive Devices", that is they contain no source of power or amplification but only attenuate or reduce the voltage signal passing through them. When used in DC circuits the voltage drop produced is measured across their terminals as the circuit current flows through them while in AC circuits the voltage and current are both in-phase producing 0o phase shift.

Resistors produce a voltage drop across themselves when an electrical current flows through them because they obey Ohm's Law, and different values of resistance produces different values of current or voltage. This can be very useful in Electronic circuits by controlling or reducing either the current flow or voltage produced across them. There are many different Resistor Types and they are produced in a variety of forms because their particular characteristics and accuracy suit certain areas of application, such as High Stability, High Voltage, High Current etc, or are used as general purpose resistors where their characteristics are less of a problem. Some of the common characteristics associated with the humble resistor are; Temperature Coefficient, Voltage Coefficient, Noise, Frequency Response, Power as well as Temperature Rating, Physical Size and Reliability.

In all Electrical and Electronic circuit diagrams and schematics, the most commonly used resistor symbol is that of a "zig-zag" type line with the value of its resistance given in Ohms, Ω

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Testing Silicon Controlled Rectifiers (SCR)

Here is a wonderful article written by my good friend Jestine Yong.

Testing SCR (silicon controlled rectifier) can be done by using an analog multi meter or specialize tester (such as the Peak electronic atlas component analyzer) designed to check semiconductor devices easily. SCR can be found in many electronic circuits. Part numbers such as the FOR3G and MCR 100-6 were very common used in computer monitor. Some called SCR as thyristor but in actual fact the word thyristor should not be associated exclusively with the silicon controlled rectifier. It is in fact a general name given to all four layer PNPN devices including the commonly used SCR. The diac, the Triac, and the SCS are the other popular devices belonging to the family of thyristors.

SCR consists of three pin of Gate (G), Anode (A) and Cathode (C). In order to identify the pin out, one must find it from semiconductor data book such the famous Philips ECG master semiconductor replacement guide. The data book will list out the general specification of the SCR such as the volt and ampere. If you want to know more details about a particular SCR, you can always try to search from the internet. Usually the SCR manufacturers will provide the full datasheet for those who want it.

Once you know the pin outs of the G, A and C legs you can begin to test the SCR. If you have the Peak electronic atlas component analyzer tester, what you need to do is to connect the three small clips to each pin of the SCR (any part number will do). The tester will begin to analyze the SCR and prompt you with the display such as "Sensitive or low power thyristor" before it tells you the exact pin outs of G, A and C. After the first test, the tester will eventually show you the answer at the LCD display. Red is Gate, Green is Cathode and Blue is Anode. It is a simple process and you will know the answer in less than 10 seconds. If there is a problem in the SCR, the tester would not be able to show the results instead it shows a shorted reading.

If you don't have this tester for checking SCR, I'm showing you another easy way on how to test SCR fast. You need an analog meter set to X1 ohm. Place the red probe to the Cathode and black probe to the Anode pin. At this time the meter doesn't show any reading. Now gently move the black probe and touch the Gate pin (the black probe still touching the Anode pin) and you will notice the meter's pointer will kick as shown at the picture (low resistance).

Removing the black probe from the GATE pin (the black probe still touching the Anode pin) you would noticed that the resistance continues to be there (low resistance). This is due to the conduction of SCR as the meter battery is usually able to supply current more than the holding current. If at this stage you removed the black probe from the Anode pin and connect it back, the pointer will dropped back to infinity (high resistance). If the SCR could hold the resistance then the SCR is considered good. If it can't hold then the SCR is faulty.

Conclusion- Practice testing SCR more often to see how's the result like. Try some different part numbers and power SCR-and if the resistance don't hold using X1 ohm, you may try X10 ohm and etc.

Jestine Yong is a electronic repairer and a writer, for more information how you can test electronic components like a professional please visit his website by clicking here.

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The Silicon-Controlled Rectifier (SCR)

SCR schematic symbol.

Shockley(no not schottky) diodes are curious devices, but rather limited in application. Their usefulness may be expanded, however, by equipping them with another means of latching. In doing so, each becomes true amplifying devices (if only in an on/off mode), and we refer to these as silicon-controlled rectifiers, or SCRs.

The progression from Shockley diode to SCR is achieved with one small addition, actually nothing more than a third wire connection to the existing PNPN structure.

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