Convert 220V AC mains electricity into five different regulated DC voltages: 5V, 9V, 12V, 15V, and 18V.

 This diagram illustrates a multiple-output linear power supply circuit designed to convert 220V AC mains electricity into five different regulated DC voltages: 5V, 9V, 12V, 15V, and 18V.

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Understanding SMD Resistor Codes In LCD Monitor

Understanding SMD resistor code is very important if you want to be able to repair LCD Monitors. EachSMD resistor has a numeric number on top of its body. It would not take you a long time to understand it as the below guidance will show you exactly how you can calculate the ohms value easily.

 0 = Jumper

000 = Jumper

6R8 = 6.8 Ohm

100 = 10 Ohm

750 = 75 Ohm

101 = 100 Ohm

 164 = 160000 = 160 Kilo Ohm

 472 = 4.7 Kilo Ohm

 1200 = 120 Ohm

 1201 =1200 Ohm= 1.2 Kilo Ohm

 1001 =1000 Ohm= 1 Kilo Ohm

 2000 = 200 Ohm

 1182 = 11800= 11.8 Kilo ohm

 1003 = 1000000= 1 Mega Ohm

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Internal Parts in LCD Monitor Atau Isi Dalem Monitor LCD

 

Currently, the most commonly used light emitting device is a fluorescent tube called a cold cathode tube for CCFL. The CCFL is called a cold cathode tube because even though the principle of illumination is the same as that of the hot cathode tubes used by indoor lamps, this lamp does not require preheating of the filament.

Also, the electrodes at the end of the bulb stay at a low temperature while emitting light. CCFL also enjoy a long life (approx 50,000 hours) without serious degradation. A special power supply, inverter, which generates approximately 600 to 1000 AC is required to drive a CCFL. This inverter is a small power supply used to make this CCFL illuminate, and is one of the important functional parts of a complete LCD display.

Display Flicker and Reddish

Normally a reddish display and display flicker in LCD Monitor were caused by one of the defective backlight (either top or bottom backlight). For those LCD Monitors that do not have the feedback circuit in the inverter board, even though the backlight have problem the LCD Monitor continue to work and never shutdown. This is totally different in LCD Monitors that have the feedback circuit in the inverter board because even a slight flicker in the display caused by a defective backlight, the LCD Monitor would immediately shutdown

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Understanding the LCD Monitor Start Circuit

 

Most of the LCD Monitor has a Start Circuit to control the voltage from the power supply to the supply pin of Inverter IC. The main control signal comes from the Main board and the voltage is from 0 and few Volts (2- 5 Volts).

If the signal is Zero Volts, then the inverter IC would not receive any supply voltage from the power supply and if the signal is 2 Volts (On) then the inverter IC would be “On” and the high voltage transformer would energized and the backlights will light up.

The Start Circuit is a good starting point to diagnose why the LCD Monitor has no display, display shutdown and intermittent no display problem.

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Understanding LCD Monitor Inverter Board

 

For a newer LCD Monitor design, the inverter board is joining together with the power board as shown in the above photo. Older LCD Monitor has the inverter board separated from the power board as shown below. 

There are four types of inverter designs (topologies) used in the LCD Monitors.

1.     Buck Royer inverter

2.     Push pull inverter (Direct Drive)

3.      Half bridge inverter and (Direct Drive)

4.      Full bridge inverter (Direct Drive)

Number 2, 3 and 4 are called Direct Drive because it eliminates the need for the inductor (buck choke) and resonant capacitors found in a conventional Royer Oscillator. In other words, Direct Drive architecture reduces component count, lower production cost and most importantly improved transformer designs that optimize performance.

In order to drive the Backlights (CCFL lamps) embedded in the panel module, an inverter circuit is required to convert the 12 volt DC up to hundreds or even a thousand plus AC voltage output. The inverter is formed by symmetric circuitry, in order to drive the separate lamp modules. The input stage (buck converter circuit) consists of Inverter IC (PWM IC), Buck P-channel FET, Buck Choke and Buck Diode. The Buck converter circuit converts a DC voltage to a lower DC voltage.

The other stage consists of a tuning capacitors, high voltage transformer, and push-pull transistor pair to boost ac output to hundreds of voltage.

The ballast capacitor controls current amplitude through the lamp negative impedance by dropping an approximately equal voltage across its positive impedance. The feedback circuit is for protection purposes and will shut down the inverter IC just in case if the high voltage produced by the high voltage transformer exceeded the normal value and also it can detect bad or a flicker backlights. The inverter IC also used to control the brightness of the CCFL lamps. The AC frequency of the high voltage transformer is typically run at 30 to 70 KHz. The higher the frequency, the greater is the light output.

Note: Some LCD Monitor design has the Buck type P-channel FET integrated into an IC thus in order to successfully testing them you can use the comparison method with another known good FET (comparing the ohms value between pins) or by using the Peak Atlas Analyzer test equipment. The IC can be in Dual in Line package or SMD type.

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