Monitor No Display – How To Repair Likom No High Voltage Problem

The criticism for this LIKOM 15″ L4031NDG Keep track of was no screen and has energy. Properly, no screen can be no significant voltage, failure in G1, G2 and heater circuit, faulty flyback transformer, failure in photograph tube and microprocessor or quite a few other explanations . In purchase to locate out the response we have to swap on the Keep track of. On switching on the keep an eye on, I could not listen to any audio from the keep an eye on but the energy led is on (eco-friendly gentle). You can not come to feel any static at the glass of the photograph tube. This could be a signal of no significant voltage symptom.

Anyhow, I have to use my devoted Kaise SK9000 significant voltage probe to test if the significant voltage existing at the anode. From time to time if you can not come to feel the static at the glass of CRT, won’t suggest that the significant voltage is not existing. It can be only reduced in significant voltage say may well be 10 to 12 kilovolts. Lower significant voltage and no significant voltage are absolutely two unique signs and symptoms. In the previously mentioned scenario, my significant voltage probe registered zero volts! So it can be verified no significant voltage difficulty.

There are quite a few explanations for no significant voltage difficulty. A lacking B+ voltage, a faulty flyback transformer, no horizontal generate pulse from h/v oscillator ic, reduced or lacking source voltage to horizontal driver transformer and and many others could trigger no significant voltage. The very first stage that I have checked was the flyback inner capacitor-the capacitance is in the typical assortment which is two.seven nanofarad. If the inner capacitor is shorted, it would trigger no significant voltage. The 2nd stage that I have checked to be all right was the B+ voltage. It confirmed about 50 + volts and this suggest there is source getting into the B+ pin of flyback transformer.

When examining the 3rd stage (the voltage at the most important winding of horizontal flyback transformer), I located that it has zero volt which is extremely strange. The foundation generate energy source enter has about 14 volts but soon after the resistor it confirmed zero volts (by proper it must have about 12 volt-voltage fall soon after the resistor). When I positioned my finger on the foundation generate energy resistor just soon after switching off the Keep track of, I could felt it was extremely very hot. Now this is what we connect with a clue. A very good functioning foundation generate energy resistor would not get very hot until it burns your finger! There have to be a thing that has long gone completely wrong or shorted that tends to make the energy resistor turned very very hot. From the final result we get, we can say that the horizontal generate circuit is obtaining difficulty so my focus is on this circuit.

A shorted horizontal driver transformer most important winding, horizontal driver transistor, factors bordering this circuit could trigger the energy resistor to transform very hot. The horizontal driver transformer most important winding can be test by utilizing a dick smith flyback tester although the horizontal driver transistor and bordering factors can be exam with a typical multimeter. The final result, amazingly not even one particular part in this circuit located to be defective.

Given that I could not identify the faulty factors, the only way to locate out the perpetrator is to appear out with my personal schematic drawing foundation on this keep an eye on circuit (utilizing keep an eye on circuit concept to resolve difficulty).

When the keep an eye on is turned on the h/v oscillator tda4858 will obtain a source voltage about nine-12 volts from energy source. Then it will ship a sq. wave pulse to horizontal driver transistor by means of pin seven (horizontal driver output) to trigger the transistor to swap. At the time the horizontal driver is switching the horizontal driver transformer would operate and a foundation sign was manufactured to transform on the Horizontal output transistor (Very hot). This Very hot would then generate the flyback transformer and 24 kilovolt would look at the anode.

I questioned myself what if the h/v oscillator ic tda4858 rather of developing a sq. pulse, it make a frequent sign? If it sends out a frequent five volts sign to the horizontal driver transistor, then this transistor would not swap and resulting in it to transform “on” all the time. If this occur, the foundation generate energy resistor and the horizontal driver transformer most important winding would experience. The foundation generate energy resistor and the horizontal driver transformer most important winding now would functions just like a filament or a lamp!. No wander the foundation generate energy resistor was receiving very hot when the keep an eye on was turned on.

Just after diligently examined the horizontal generate circuit, I have built the summary that it was the h/v oscillator tda4848 that sends a completely wrong sign resulting in the foundation generate energy resistor to get very hot and at the exact time resulting in no significant voltage in the keep an eye on. I did not use an oscilloscope to test for the sq. wave in purchase to verify my concept proper due to the fact I am extremely selected that it was the h/v oscillator IC that output a completely wrong sign that prompted no significant voltage.

You would not consider this sure it was this perpetrator (TDA4858) that prompted the keep an eye on no screen difficulty. Just after changing the IC, the significant voltage right away energized and the zero volts calculated at the pin of horizontal driver transformer now confirmed 12 volts! What a relieved and a good gratification in my coronary heart. I consider if we continue on to swap on the Keep track of for a for a longer period time period, both the foundation generate energy resistor or the horizontal driver transformer most important winding would burnt out resulting in it to open up circuit.

Fixing Displays have to have endurance, comprehending how Keep track of operate and its sign and also the proper way to exam digital factors. If the functional way can not resolve a difficulty, you can normally use the concept way to assist you out. Hence it is significant to know on how to examine a keep an eye on schematic diagram. Never give up and continue on to study and I consider one particular working day you shall attained what is preferred in your coronary heart! Have a very good working day!

Jestine Yong

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