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

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

The objection for this LIKOM 15″ L4031NDG Monitor was no showcase and has power. All things considered, no showcase can be no high voltage, disappointment in G1, G2 and radiator circuit, imperfect flyback transformer, disappointment in picture cylinder and chip or numerous different reasons . To discover the appropriate response we need to turn on the Monitor. After turning on the screen, I was unable to hear any stable from the screen however the force drove is on (green light). You can’t feel any static at the glass of the image tube. This could be an indication of no high voltage side effect.

At any rate, I need to utilize my devoted Kaise SK9000 high voltage test to check if the high voltage present at the anode. At times in the event that you can’t feel the static at the glass of CRT, doesn’t imply that the high voltage is absent. It’s just low in high voltage; say might be 10 to 12 kilovolts. Low high voltage and no high voltage are absolutely two unique side effects. In the above case, my high voltage test enrolled zero volts! So it’s affirmed no high voltage issue.

There are numerous purposes behind no 2CL2FM issue. A missing B+ voltage, a deficient flyback transformer, no level drive beat from h/v oscillator ic, low or missing inventory voltage to flat driver transformer and so on could cause no high voltage. The main point that I have checked was the flyback interior capacitor-the capacitance is inside the ordinary reach which is 2.7 nanofarad. In the event that the inward capacitor is shorted, it would cause no high voltage. The second point that I have checked to be alright was the B+ voltage. It appeared around 50 + volts and this mean there is supply entering the B+ pin of flyback transformer.

While checking the third point (the voltage at the essential twisting of even flyback transformer), I found that it has zero volt which is strange. The base drive power supply input has around 14 volts yet after the resistor it showed zero volts (by right it ought to have around 12 volt-voltage drop after the resistor). At the point when I put my finger on the base drive power resistor soon after turning off the Monitor, I could felt it was extremely hot. Presently this is the thing that we call a hint. A decent working base drive power resistor will not get hot till it consumes your finger! There should be something that has turned out badly or shorted that makes the force resistor turned very hot. From the outcome we get, we can say that the flat drive circuit is having issue so my fixation is on this circuit.

A shorted flat driver transformer essential winding, level driver semiconductor, parts encompassing this circuit could make the force resistor turn hot. The level driver transformer essential winding can be check by utilizing a dick smith flyback analyzer while the flat driver semiconductor and encompassing parts can be test with a typical multimeter. The outcome, shockingly not so much as one part in this circuit discovered to be broken.

Since I was unable to find the flawed parts, the best way to discover the offender is to come out with my own schematic drawing base on this screen circuit (utilizing screen circuit hypothesis to tackle issue).

At the point when the screen is turned on the h/v oscillator tda4858 will get a stockpile voltage around 9-12 volts from power supply. At that point it will send a square wave heartbeat to flat driver semiconductor through pin 7 (even driver yield) to make the semiconductor switch. When the level driver is exchanging the even driver transformer would work and a base sign was created to turn on the Horizontal yield semiconductor (HOT). This HOT would then drive the flyback transformer and 24 kilovolt would show up at the anode.

I asked myself imagine a scenario in which the h/v oscillator ic tda4858 as opposed to creating a square heartbeat, it produce a consistent sign. In the event that it conveys a consistent 5 volts sign to the flat driver semiconductor, at that point this semiconductor would not switch and making it turn “on” constantly. On the off chance that this occur, the base drive power resistor and the level driver transformer essential winding would endure. The base drive power resistor and the flat driver transformer essential twisting currently would acts very much like a fiber or a light!. No meander the base drive power resistor was getting hot when the screen was turned on.

After deliberately contemplated the even drive circuit, I’ve made the end that it was the h/v oscillator tda4848 that conveys an off-base message causing the base drive power resistor to get hot and simultaneously causing no high voltage in the screen. I didn’t utilize an oscilloscope to check for the square wave to demonstrate my hypothesis right since I’m sure that it was the h/v oscillator IC that yield an off-base sign that caused no high voltage.

You would not accept this; yes it was this guilty party (TDA4858) that caused the screen no presentation issue. In the wake of supplanting the IC, the high voltage promptly invigorated and the zero volts estimated at the pin of flat driver transformer presently showed 12 volts! What an eased and an incredible fulfillment in my heart. I accept in the event that we keep on turning on the Monitor for a more drawn out period, either the base drive power resistor or the level driver transformer essential winding would wore out making it open circuit.

Fixing Monitors need persistence, seeing how Monitor work and its sign and furthermore the correct method to test electronic segments. In the event that the commonsense way can’t take care of an issue, you can generally utilize the hypothesis approach to take care of you. Consequently it is critical to know on the best way to peruse a screen schematic chart. Try not to surrender and proceed to learn and I trust one day you will accomplished what’s ideal in your heart! Have a decent day!

 

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