Sunday, July 24, 2011

Viewsonic VG1930WM no power, repaired

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.




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.

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

Viewsonic VX910 no power, repaired

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.







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.


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

Monday, June 20, 2011

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



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.


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

Sunday, June 19, 2011

HPT4234, HPT4254,HPT4264, BN44-00161A and BN00162A power supplies repaired



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.

HPT4254X/XAA, BN44-00161A Professional Repair:
If you are interested in having a BN44-00161A, BN44-00162A or any other power supply repaired professionally then you may be interested in our mail in repair services. We can do the repair on BN44-00161A and BN44-00162A power supplies for $50 plus the cost of return shipping and handling. Click here to see our mail in repair service page.


HPT4254X/XAA, BN44-00161A Repair Kits:
Repair kits for the BN44-00161A and BN44-00162A power supply available from Preher-Tech.
Click here to visit our parts kits sales page.

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

Wednesday, June 8, 2011

Samsung HPT5044 (HPT5044X/XAA) BN44-00162A power supply repaired.

HPT4254X/XAA, BN44-00162A Professional Repair:
If you are interested in having a BN44-00161A, BN44-00162A or any other power supply repaired professionally then you may be interested in our mail in repair services. We can do the repair on BN44-00161A and BN44-00162A power supplies for $50 plus the cost of return shipping and handling. Click here to see our mail in repair service page.


HPT4254X/XAA, BN44-00162A Repair Kits:
Repair kits for the BN44-00161A and BN44-00162A power supply available from Preher-Tech.
Click here to visit our parts kits sales page.

Samsung HPT5044 (HPT5044X/XAA)BN44-00162A power supply repaired.
This repair was basically a very similar repair to one we often do on the HPT4254, BN44-00161A 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 BN44-00161A 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.


HPT4254X/XAA, BN44-00162A Professional Repair:
If you are interested in having a BN44-00161A, BN44-00162A or any other power supply repaired professionally then you may be interested in our mail in repair services. We can do the repair on BN44-00161A and BN44-00162A power supplies for $50 plus the cost of return shipping and handling. Click here to see our mail in repair service page.


HPT4254X/XAA, BN44-00162A Repair Kits:
Repair kits for the BN44-00161A and BN44-00162A power supply available from Preher-Tech.
Click here to visit our parts kits sales page.


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

Wednesday, May 25, 2011

Testing HV transformers in LCD TV inverter circuits






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.








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

Friday, May 13, 2011

The BLUE Ring Tester





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.

Tuesday, April 12, 2011

The BLUE ESR Meter





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




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.


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

Wednesday, March 16, 2011

Electronics repair training videos





















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



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



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.

Saturday, March 5, 2011

Typical electrolytic capacitor ESR values


This is a chart showing typical ESR values for good electrolytic capacitors. A faulty capacitor can often have a value that is 10X the value stated on this chart before it starts to cause problems in most circuits, of course this is not always the case and not for all of the capacitance values listed. This is the same ESR chart found on the original Dick Smith ESR meter and the also 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

Sunday, February 13, 2011

LCD TV Display Failure Symptoms and Possible Causes.




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.

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



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

Saturday, February 12, 2011

Oscilloscope Tutorial


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.

Tuesday, January 11, 2011

How to repair LCD TVs


"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)



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".

Remember to visit www.preher-tech.com

Thermistors


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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Remember to visit www.preher-tech.com