Preher-Tech Blog

Viewsonic VG1930WM no power, repaired

2011-07-24T23:19:00.000-07:00

I just finished repairing a Viewsonic VG1930WM that had no power, no standby LED, completely dead. I opened up the monitor and checked the output voltages from the power supply and both were present and stable. I verified that the 5V was still present at the main board. Next I checked the output from the 3.3V and 1.8V linear voltage regulator ICs on the main board and the 3.3V regulator's output was considerably low around 2.2V, the output from the 1.8V regulator was also very low but it gets its input from the 3.3V regulator so it makes sense that the 1.8V regulators voltage was low. I replaced the 3.3V regulator after verifying it was faulty and the monitor was still dead when I plugged it in to check voltages again, the 3.3V regulator's output was now within tolerance so I again checked the output from the 1.8V regulator and it was still low about 1.2V, so I then replaced the 1.8V regulator and when I plugged the monitor in to check the output from the 1.8V regulator I saw the standby light turn on, the voltage output from the 1.8V regulator was now within tolerance and the monitor turned on and functioned flawlessly.

Preher-Tech's mail in repair service:
http://preher-tech.com/mailinrepairservice.aspx

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Viewsonic VX910 no power, repaired

2011-07-24T23:00:00.000-07:00

Recently did a repair on a Viewsonic VX910 that had no power, no standby LED, totally dead. Upon opening the monitor I could see that someone had already replaced all the electrolytic capacitors in the output filter circuitry, but for this type of failure I normally don't suspect the filter capacitors anyways. I plugged the monitor in to check for any output voltages from the PSU and I could here a faint chirping coming from the power supply, this is always a good indication of a shorted output diode or faulty components in the feedback circuitry, the power supply is continually trying to start up and then shutting down,over and over. As I suspected there was no output from the power supply. I pulled the power supply and the first thing I checked was the dual schotttky diode D660 and one of the diodes in the dual package was shorted. The original diode was a MBR10100CT dual schottky diode, I replaced it with a B20100G dual schottky diode. After replacing the dual diode the monitor powered on and worked once again.

Preher-Tech's mail in repair service:
http://preher-tech.com/mailinrepairservice.aspx

Also don't forget to visit http://www.preher-tech.com/

Philips 37MF321D/37, 37MF331D/37, 715T2056-1 Power Supply Repair

2011-06-20T23:35:00.000-07:00

We have been receiving quite a few 715T2056-1 power supplies for repair from Philips 37MF321D/37 and 37MF331D/37 LCD TVs. The failure symptom is typically that the green standby/power indicator led blinks constantly and the TV will not turn on. The most common reason this particular power suppy fails is the 2200uF 25V capacitor at location 2074 has puffed and vented or has a significantly high ESR, some of the other electrolytic filter capacitors on the secondary side of the power supply may have a high ESR as well. The 9.1V 0.5W zener diode(BZX79C9V1 is used for replacement) at location 6079 is commonly shorted, but may also be open as well. The SMD 2.2 ohm 0.125W resistor at location 3045 has opened and is usually burned often damaging the copper trace on the bottom of the PCB. Parts are available from http://www.mouser.com/. If you have any questions regarding this repair or any other electronics related questions please feel free to email me john@preher-tech.com.

Professional Repair:
If you are interested in having your power supply board repaired professionally then you may be interested in our mail in repair services. We can do the repair on this particular power supply for $50 plus the cost of return shipping and handling. Click here to see our mail in repair service page. You can also email contactus@preher-tech.com for more information.

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HPT4234, HPT4254,HPT4264, No power, Clicking, Repaired

2011-06-19T22:53:00.000-07:00

If you have a Samsung HPT4234, HPT4254 or HPT4264 that does not turn on and only clicks or intermittently shuts down and starts clicking and you are looking for information on how to repair the power supply, see our post on how to repair the HPT4254 power supply which also applies to the HPT4234 and HPT4264 power supplies by clicking here.

Professional Repair:
If you are interested in having your power supply board repaired professionally then you may be interested in our mail in repair services. We can do the repair on this particular power supply for $50 plus the cost of return shipping and handling. Click here to see our mail in repair service page.

Take care and remember to visit http://www.preher-tech.com/

Samsung HPT5044 (HPT5044X/XAA) no power, clicking, repaired.

2011-06-08T16:54:00.000-07:00

Samsung HPT5044 (HPT5044X/XAA) no power, clicking, repaired.

This repair was basically a very similar repair to one we often do on the HPT4244 power supplies, but we wanted to give this one it's own post so that people searching for info on the HPT5044 with the failure of no power only clicking when attempting to turn the TV on or also intermittent power and clicking, would be able to easily find this info when searching online. The HPT4244 power supplies that we have been receiving for repair come in with an open fuse at location F803, shorted MOSFETs at locations QS801 and QS802 and open SMD dual package diodes at locations DS801 and DS802. QS801 and QS802 are both AV218N50 MOSFETs, but we substitute with FDA18N50 MOSFETs. F803 is an 8A 250V time delay/slow blow fuse. DS801 and DS802 are both 1SS184T5LFT, UFR dual package common cathode SMD diodes. All parts are available from http://www.mouser.com/.

Click here to read the repair info on the power supply from the HPT4254 which is extremely similar. There is some good info in this post including other components you will want to test if MOSFETs QS801 and QS802 are not shored or F803 is not open as these boards have multiple failures that can happen.

Professional Repair:
If you are interested in having this board repaired professionally then you may be interested in our mail in repair services. We can do the repair on this particular power supply for $50 plus the cost of return shipping and handling. Click here to see our mail in repair service page.

Remember to visit http://www.preher-tech.com/.

Testing HV transformers in LCD TV inverter circuits

2011-05-25T12:02:00.000-07:00

This article is from the Preher-Tech May 2011 newsletter. In this article I show you how easy it is to test LCD TV inverter transformers.

Click here to download the article "Testing HV Transformers in LCD TVs"

Also if you are interested in receiving articles like this sent to your inbox each month the join the Preher-tech newsletter by clicking here.

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The BLUE Ring Tester

2011-05-13T10:25:00.000-07:00

Preher-Tech is now selling the BLUE ring tester fully assembled by us and in kit form as well.

Click here to visit our sales page and get more info.

The BLUE ESR Meter

2011-04-12T19:15:00.000-07:00

Preher-Tech is now selling the BLUE ESR Meter fully assembled by us and in kit form as well.

Click here to visit our sales page and get more info.

Sharp Aquos LC32D43U no power

2011-04-12T11:46:00.000-07:00

Here is an article from this month's newsletter about a repair we did on a Sharp Aquos LC32D43U that had no power or standby light, totally dead. Click here to download the article "Sharp Aquos LC32D43U No Power"

Professional Repair:
If you are interested in having this board repaired professionally then you may be interested in our mail in repair services. We can do the repair on this particular power supply for $50 plus the cost of return shipping and handling. Click here to see our mail in repair service page.

Repair Kit:
We also have a repair kit for the power supply available for $35.00 which the parts necessary for this repair and includes USPS priority shipping within the contiguous United States. Click here to visit our repair kits page and purchase this kit.

For more repair and other electronics related articles join the Preher-Tech newsletter by clicking here.

Remember to visit http://www.preher-tech.com/

Electronics repair training videos

2011-03-16T23:34:00.000-07:00

Click here to visit Randy Fromm's YouTube page and see more of his great videos.

Also click here to see Randy Fromm's Arcade Schools training programs.

Randy Fromm's Arcade School offers a wide range of video training programs, from beginning electronics to advanced microprocessor repair.

Randy Fromm's Electronics Repair Guides

2011-03-16T21:42:00.000-07:00

Here is a great website to purchase some really good electronics repair guides by Randy Fromm, http://randyfromm.com/shopping/

Randy Fromm's Arcade School offers a wide range of video training programs, from beginning electronics to advanced microprocessor repair.

Here is a list if some of the available programs:

-Randy Fromm's Big Blue Book of Really Great Technical Information
-Randy Fromm's Big Green Book of Monitor Schematics
-All-You-Need Beginning Electronics for Operators and Mechanics
-Basic Videogame Troubleshooting
-Diodes, Transistors & Other Semiconductors
-Switching Regulator Power Supplies (Peter Chou type)
-Conventional Power Supplies
-Videogame Monitor Repair Made Simple
-Using a Digital Multimeter
-Using an Oscilloscope
-Introduction to Digital Electronics
-Troubleshooting Microprocessor Based Systems

Click here for more information and to visit the sales page.

Typical electrolytic capacitor ESR values

2011-03-05T18:25:00.000-08:00

Here is a chart showing typical ESR values for good electrolytic capacitors. For many of the capacitor values listed the ESR will typically have a value 10X the value on this chart before it starts to cause problems in most circuits. This is the same ESR chart found on the original Dick Smith ESR meter and the current EVB ESR meter.

Click here to download the ESR chart.

Remember to visit http://www.preher-tech.com/ and if you have any questions you can email me john@preher-tech.com

LCD TV Display Failure Symptoms and Possible Causes.

2011-02-13T21:15:00.000-08:00

This is a 6 page guide that shows LCD TV display failure symptoms such as vertical bars and lines or noise/distorsion in display etc and what the possible cause of failure may be.

Click here to download PDF file of LCD TV Display Failure Symptoms and Possible Causes.

Don't forget to visit http://www.preher-tech.com/

Oscilloscope Tutorial

2011-02-12T21:54:00.000-08:00

Thought all my readers would enjoy this, it;s from nutsvolts.com the online home of Nuts & Volts Magazine.

Afrotechmods shows us what an Oscilloscope is and how to use it… An oscilloscope is the most important piece of electronic test equipment you can buy after a multimeter. They allow you to see, in great detail, what is going on with all the voltages in your circuit. If you ever work with audio circuits, timers, micro controllers or radios etc... an oscilloscope will help you get the job done.

Click here for the full article and videos.

How to repair LCD TVs

2011-01-11T12:46:00.000-08:00

"Troubleshooting and Repairing LCD TVs"
If you are interested in repairing LCD TVs then click here to check out the top selling LCD TV Repair Guide.
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You may also be interested in Kent Liew's LCD TV Repair Membership Site. This is a great place to get training manuals, service manuals, schematics and more. Click here to read more.

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Remember to visit http://www.preher-tech.com/

How To Repair SMPS(Switch Mode Power Supply)

2011-01-11T12:36:00.000-08:00

Had to mention this book again, it is one of my favorite books written by Jestine Yong.

This guide is a must have for anyone who is in the electronics repair field or who is trying to impove their electronics troubleshooting an repair skills. This 271 page guide will teach you all you need to know about Switch Mode Power Supplies and how to troubleshoot and repair them. Switch mode power supplies are used in most consumer electronics today and are the most common cause of failure for all types of electronics devices.

Click here to read more about the ebook "Troubleshooting and Repairing Switch Mode Power Supplies".

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Thermistors

2011-01-11T12:02:00.000-08:00

A thermistor is a type of resistor whose resistance varies significantly (more than in standard resistors) with temperature. The word is a portmanteau of thermal and resistor. Thermistors are widely used as inrush current limiters, temperature sensors, self-resetting overcurrent protectors, and self-regulating heating elements.
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Thermistors differ from resistance temperature detectors (RTD) in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. The temperature response is also different; RTDs are useful over larger temperature ranges, while thermistors typically achieve a higher precision within a limited temperature range [usually −90 °C to 130 °C].

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PTC thermistors can be used as current-limiting devices for circuit protection, as replacements for fuses. Current through the device causes a small amount of resistive heating. If the current is large enough to generate more heat than the device can lose to its surroundings, the device heats up, causing its resistance to increase, and therefore causing even more heating. This creates a self-reinforcing effect that drives the resistance upwards, reducing the current and voltage available to the device.

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PTC thermistors are used as timers in the degaussing coil circuit of most CRT displays and televisions. When the display unit is initially switched on, current flows through the thermistor and degaussing coil. The coil and thermistor are intentionally sized so that the current flow will heat the thermistor to the point that the degaussing coil shuts off in under a second. For effective degaussing, it is necessary that the magnitude of the alternating magnetic field produced by the degaussing coil decreases smoothly and continuously, rather than sharply switching off or decreasing in steps; the PTC thermistor accomplishes this naturally as it heats up. A degaussing circuit using a PTC thermistor is simple, reliable (for its simplicity), and inexpensive.
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NTC thermistors are used as resistance thermometers in low-temperature measurements of the order of 10 K.
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NTC thermistors can be used as inrush-current limiting devices in power supply circuits. They present a higher resistance initially which prevents large currents from flowing at turn-on, and then heat up and become much lower resistance to allow higher current flow during normal operation. These thermistors are usually much larger than measuring type thermistors, and are purposely designed for this application.
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NTC thermistors are regularly used in automotive applications. For example, they monitor things like coolant temperature and/or oil temperature inside the engine and provide data to the ECU and, indirectly, to the dashboard.
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NTC thermistors can be also used to monitor the temperature of an incubator.
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Thermistors are also commonly used in modern digital thermostats and to monitor the temperature of battery packs while charging.

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TV and electronics repair in Edmonds Washington

2010-12-16T19:21:00.000-08:00

We specialize in LCD TV and monitor repair

206-734-8852
Or
1-800-691-7422

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, http://www.preher-tech.com/

TV and electronics repair in Seattle Washington

2010-12-16T19:15:00.000-08:00

Preher-Tech

We specialize in LCD TV and monitor repair

206-734-8852
Or
1-800-691-7422

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, www.preher-tech.com

Dip meter

2010-12-08T16:22:00.001-08:00

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

2010-12-08T16:19:00.000-08:00

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

2010-12-08T16:03:00.000-08:00

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.

Boost converter

2010-12-01T14:57:00.000-08:00

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

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Buck converter

2010-12-01T14:30:00.000-08:00

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

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Electret microphone

2010-11-29T16:03:00.000-08:00

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.