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

The protest for this LIKOM 15″ L4031NDG Monitor was no presentation and has power. Indeed, no presentation can be no high voltage, disappointment in G1, G2 and radiator circuit, imperfect flyback transformer, disappointment in picture cylinder and microchip 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 solid 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 manifestation.

In any case, I need to utilize my reliable Kaise SK9000 high voltage test to check if the high voltage present at the anode. Here and there 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 distinct indications. In the above case, my high voltage test enlisted zero volts! So it’s affirmed no high voltage issue.

There are numerous purposes behind no high voltage issue. A missing B+ voltage, a deficient flyback transformer, no level drive beat from h/v oscillator ic, low or missing stockpile voltage to flat driver transformer and so forth could cause no high voltage. The primary point that I have checked was the flyback inner capacitor-the capacitance is inside the typical reach which is 2.7 nanofarad. In the event that the inside capacitor is shorted, it would cause no high voltage. The second point that I have checked to be OK 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 voltageĀ high voltage fast recovery rectifier diode at the essential twisting of level flyback transformer), I found that it has zero volt which is surprising. 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 set my finger on the base drive power resistor soon after turning off the Monitor, I could felt it was exceptionally 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 incredibly hot. From the outcome we get, we can say that the level drive circuit is having issue so my focus is on this circuit.

A shorted level driver transformer essential winding, even driver semiconductor, parts encompassing this circuit could make the force resistor turn hot. The even 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 segment in this circuit discovered to be flawed.

Since I was unable to find the deficient 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 stock voltage around 9-12 volts from power supply. At that point it will send a square wave heartbeat to even driver semiconductor through pin 7 (flat driver yield) to make the semiconductor switch. When the level driver is exchanging the even driver transformer would work and a base sign was delivered 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 consider the possibility that the h/v oscillator ic tda4858 as opposed to creating a square heartbeat, it produce a consistent sign. On the off chance that it conveys a steady 5 volts sign to the even driver semiconductor, at that point this semiconductor would not switch and making it turn “on” constantly. In the event that this occur, the base drive power resistor and the even driver transformer essential winding would endure. The base drive power resistor and the level driver transformer essential twisting presently would acts actually like a fiber or a light!. No meander the base drive power resistor was getting hot when the screen was turned on.