The criticism of this LIKOM 15″ L4031NDG Monitor was that it had no display and no power. No present can be no high discord, failure in G1, G2, and heater circuit, malfunctioning flyback transformers, failure with a picture tube and micro-processor, or many other reasons. When I decided I wanted to find the answer, we had to start the Monitor. Upon transferring to the monitor, I could not hear any sound, but the power was on (green light). You can’t feel any permanent at the glass of the graphic tube. This could be a sign connected with no high voltage warning sign.
Anyhow, I have to use my very own faithful Kaise SK9000 substantial voltage probe to check if positive aspects of voltage are present at the anode. Sometimes if you can’t feel the permanent at the glass of CRT, it doesn’t mean that the high discord is not present. It’s solely low in high voltage, declared maybe 10 to 14 kilovolts. Low high discord and no high voltage usually are two different indicators. In the above case, my substantial voltage probe registered absolutely nothing volts! So it’s confirmed not any high voltage problem.
There are various reasons for the high discord problem. A missing B+ voltage, a defective flyback transformer, no horizontal commute pulse from the h/v oscillator, the low or incomplete supply voltage to the apaisado driver transformer, etcetera, could cause no high discord. The first point that I included checked was the flyback inner surface capacitor-the capacitance is within the typical range, which is 2 . 6 nano farad. If the internal capacitor is shorted, it will bring about no high voltage. Another point that I have inspected to be okay was the B+ voltage. It showed about 50 + volts. This also means a supply steals into the B+ pin connected with a flyback transformer.
When looking at the third point (the discord at the primary winding connected with the horizontal flyback transformer), I stumbled upon that it has zero watts which is very unusual. The bottom drive power supply input provides about 14 volts, yet after the resistor, it demonstrated zero volts (by proper, it should have about ten volt-voltage drop after the resistor). I could feel it boiling when I placed my ring finger on the base drive strength resistor just after switching off the Monitor. Now, this is what we all call a clue. An excellent working base drive strength resistor won’t get warm till it burns your current finger! There must be something that moved wrong or shorted, producing the power resistor turned incredibly hot. Our result shows that the side-to-side drive circuit is having challenges, so my concentration is definitely on this circuit.
A shorted horizontal driver transformer, the most crucial winding, horizontal driver radio, and components surrounding these rounds could cause the power resistor to switch to hot. The horizontal driver’s transformer primary winding is usually checked by using a dick jones flyback tester. In contrast, the apaisado driver transistor and associated components can be tested along with a standard multimeter. Interestingly, not even one component on this circuit was found to be wrong.
Since I could not often locate the defective components, the only way to uncover the culprit was to come out with my schematic drawing base within this monitor circuit (using display circuit theory to solve the problem).
When the monitor is fired up, the h/v oscillator tda4858 will receive a supply discorde of about 9-12 volts by the power supply. Then it will mail a square wave rhythm to the horizontal driver radio through pin 7 (horizontal driver output) to bring the transistor to the switch. As the horizontal driver is transferring, the horizontal driver transformer works, and a base indication is produced to turn on often the Horizontal output transistor (HOT). This HOT would, in that case, drive the flyback transformer and 24 kilovolts at the anode.
I asked myself, what if the h/v oscillator ic tda4858, instead of designing a square pulse, it causes a constant signal? If it discharges a constant 5 volts indicated to the horizontal driver radio, then this transistor would not transition, causing it to switch “on” all the time. If this comes about, the base drive power resistor and the horizontal driver transformer primary winding will go through. The base drive power resistor and the horizontal driver transformer’s primary winding will now act just like a filament or a lamp! No wonder the primary drive power resistor seemed to be getting hot when the display was turned on.
After properly studying the horizontal commute circuit, I’ve concluded that the h/v oscillator tda4848 sent an incorrect signal causing the base commute power resistor to get warm and, at the same time, causing no large voltage in the monitor. Some use an oscilloscope to check for that square wave to demonstrate my theory right because I’m very sure that the h/v oscillator IC output a wrong sign that caused no large voltage.
You would not feel this; yes, this specific culprit (TDA4858) induced the monitor no-show problem. After replacing the particular IC, the high voltage was energized immediately, and the zero v measured at the pin regarding the horizontal driver transformer today showed 12 volts! How relieved and great pleasure in my heart. I believe once we switch on the Screen for a more extended period, the base drive power resistor and the horizontal driver transformer primary winding would lose out, causing it to spread out the circuit.
Repairing Monitors will need patience, an understanding of how Monitors perform and their signal, and also the proper way to test electronic parts. If the practical way isn’t to solve a problem, you can always utilize the theory to help you out. Hence it is essential to know how to study and monitor schematic plans. Don’t give up, and always learn, and I believe at some point, you shall achieve precisely what is desired in your heart! Use a good day!
