Preher-Tech Blog

Samsung HPS4253 no power, PSPF391A01A / BN96-03252A power supply repair

2014-03-26T01:34:00.000-07:00

Repair service for Samsung PSPF391A01A / BN96-03252A power supply which is used in the following Samsung Models,

HPR4272X/XAA, HPS4233X/XAA, HPS4233X/XAC SD03, HPS4233X/XAC SG04, HPS4233X/XAC SD01, HPS4233X/XAC SG02, HPS4253X/XAA, HPS4253X/XAC SD01, HPS4253X/XAC 0001, HPS4253X/XAC SD03, HPS4253X/XAC SG02, HPS4253X/XAC SG04, HPS4273X/XAA and SPS4243X/XAA

Typical failure symptoms that indicate power supply failure: No power. Totally dead, no standby LED and does not respond to buttons being pressed. TV shuts down immediately after being turned on. TV makes a clicking sound.

If you are interested in having a PSPF391A01A / BN96-03252A power supply or any other power supply repaired professionally contact johnpreher@gmail.com

Thank you for visiting our blog and remember to also visit www.preherservices.com

Sony BRAVIA KDL40EX600, no power, APS-272(CH) power supply repair

2014-02-24T01:27:00.007-08:00

Sony BRAVIA KDL-40EX600

Failure symptom: No power

Upon diagnosis of the power supply I found that power MOSFETs Q6101 and Q6102 were shorted between source,drain and gate and fusible resistor R6536 was open. Power MOSFETs Q6101 and Q6102 were 2SK4096 , 8 amp, 500 volt, N channel MOSFETs and were replaced with substitutes, FQPF9N50CF 9 amp, 500 volt MOSFETs. Resistor R6536 was a 1/2 watt 0.47 ohm fusible resistor.

After replacing the faulty components and installing the power supply the TV turned on and was completely functional.

KDL-55EX500, APS-272(CH) Professional Repair:

If you are interested in having an APS-272(CH) or any other power supply repaired professionally then contact johnpreher@gmail.com

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Sony BRAVIA KDL-55EX500, no power, APS-256(CH) power supply repair

2014-02-24T01:20:00.000-08:00

Sony BRAVIA KDL-55EX500

Failure symptom: No power

Upon diagnosis of the power supply I found that power MOSFETs Q6304 and Q6305 were shorted between source and drain and fusible resistor R6350 was open. Power MOSFETs Q6304 and Q6305 were 2SK4096 , 8 amp, 500 volt, N channel MOSFETs and were replaced with substitutes, FQPF9N50CF 9 amp, 500 volt MOSFETs. Resistor R6350 was a 1/2 watt 0.47 ohm fusible resistor.

After replacing the faulty components and installing the power supply the TV turned on and was completely functional.

KDL-55EX500, APS-256(CH) Professional Repair:

If you are interested in having an APS-256(CH) or any other power supply repaired professionally contact johnpreher@gmail.com

Thank you for visiting our blog and remember to also visit www.preherservices.com

Samsung power supply repair

2012-10-02T15:14:00.003-07:00

HPT4254X/XAA, BN44-00161A Professional Repair:
If you are interested in having a BN44-00161A, BN44-00162A or any other power supply repaired professionally visit preherservices.com

Preher Services offers mail in repair service on power supplies for the following Samsung models,

Samsung HPT42
Samsung HPT4234X/XAA
Samsung HPT4234X/XAC
Samsung HPT4254
Samsung HPT4254W
Samsung HPT4254X
Samsung HPT4254X/XAA
Samsung HPT4254X/XAC
Samsung HPT4254X/XAP
Samsung HPT4264X/XAA
Samsung HPT4264X/XAC
Samsung PL42C71HDPX/XAX
Samsung PL42C71HPX/XAX
Samsung PL42C91HPX/RCL
Samsung PL42C91HPX/STR
Samsung PL42C91HPX/XAP
Samsung PL42C91HPX/XAX
Samsung PL42Q91HDPX/XAX
Samsung PL42Q91HPX/XAO
Samsung HPT5034X/XAA
Samsung HPT5034X/XAC
Samsung HPT5044
Samsung HPT5044X
Samsung HPT5044X/XAA
Samsung HPT5054X/XAA
Samsung HPT5064X/XAA

If sending your power supply, TV should have one of the following failure symptoms:

-Clicking
-shuts down
-goes on/off by itself
-No power-won't come on-dead

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.

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Viewsonic VX910 no power, repaired

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

I recently did a repair on a Viewsonic VX910 that had no power. Upon opening the monitor I could see that someone had already replaced all the electrolytic capacitors on the power supply secondary side. I plugged the monitor in and attempted to power on 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 removed 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.

Learn how to repair any power supply...

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Ask about our 3 day power supply repair course.

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/.

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

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

If you are interested in having a BN44-00161A, BN44-00162A or any other power supply repaired professionally then email johnpreher@gmail.com

Visit www.preherservices.com

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

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

To learn how I repaired this power supply email johnpreher@gmail.com

HPT4254X/XAA, BN44-00162A Professional Repair:
If you are interested in having a BN44-00161A, BN44-00162A or any other power supply repaired professionally visit http://www.preherservices.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"

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Typical electrolytic capacitor ESR values

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

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.

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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/distortion 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.

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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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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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Multivibrators

2010-11-23T15:43:00.000-08:00

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.

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Logic Gates

2010-11-16T15:24:00.000-08:00

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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Operational Amplifiers

2010-11-09T15:54:00.000-08:00

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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Make Your Own Ring Tester

2010-11-06T18:21:00.000-07:00

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 winding of SMPS transformers for shorted windings and also the primary and secondary windings of high voltage transformers found in inverter circuits along with other high Q inductive components.

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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Testing Semiconductors

2010-11-01T12:01:00.000-07:00

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 www.preher-tech.com for all kinds of electronics information.

The TRIAC

2010-11-01T11:55:00.000-07:00

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

2010-11-01T11:49:00.000-07:00

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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