How To Repair Lcd Monitors
The LCD display backlight is a cold cathode fluorescent light (CCFL), which requires a high voltage during normal operation. The starting voltage may be as high as 1000 VRMS, the running voltage is about 300 VRMS at 3 ma. This voltage is produced by a resonant Royer oscillator which produces a sinusoidal output waveform at about 50 kHz. The transistors Q305 and Q306 receive their base drive from the transformer. The output waveform is the result of the transformer inductance resonating with C352 and the CCFL reflected capacitance.
The LCD display requires a negative bias voltage (LCDBIAS) that adjusts the contrast of the display. The bias supply is thus an adjustable regulator, controlled by digital signals from the processor. The design is a modified buck regulator whereby the switch is Q307, the output inductor is L309, and the catch diode is D313. In the modified design, the output is taken from the bottom of the catch diode in order to produce a negative voltage. The output voltage is monitored by the regulator via R336. Output current is limited by R337. The output voltage setpoint is established by a DAC inside U307 set by processor signals LCDADJ and LCDCTRL.
Turn on the power of removable drive and then VR800. The VR800 LCD display shows No Disk . 6. Insert the diskette with updated software file. The VR800 LCD display shows No Disk , Initial , name of drive (e.g. ZIP 100) and updated software file name in order and comes to a standstill at the display below. Memorize the displayed ROM version and date before updating the software.
This group of tests is used to verify functionality of the switches, LED's, VOLUME knob, LCD display, logo illumination, etc. The tests include Character Test Block Test Switch Test LED Test AC3 SPI Test AC3 MEM Test Contrast Test This test verifies the functionality of the IR Remote. Press a key on the remote and verify that the LCD displays the hexadecimal code identifying the key. The hex display on the LCD remains unchanged until another remote key is pressed. While the remote key is being pressed the IR acknowledge LED will flash and the LCD displays the IR icon along with the hex value. To exit the test, hold down the front panel BYPASS button and press MUTE. When you have successfully exited the test the LCD will display an arrow on the left side pointing to the word REMOTE.
This mode tests if all the segments on the LCD display and the LEDs on the FD-4 top panel are correctly working or not. If the FD-4 is in a normal condition, all the segments on the LCD display will lit solid and the LEDs on the top panel will start blinking. If the FD-4 is not in a normal condition, the faulty segments on the LCD display and or LEDs on the top panel will remain unlit.
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