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LG 575LE BackLight Problem

18 Cze 2009 05:22 1900 3
  • Poziom 12  
    Hi all colleagues
    i've got this LG 575LE based on Chassis CL-18 dead after repairing power supply i've got stable 5.1V and all the 4 BA033 are getting 5.1V and produce the 3.3V and everything is ok ,the main fuse in the inverter circuit was alo open and after replacing it and powering the monitor up , the monitor power up normally and has OSD and the picture is normal , the only problem now is the backlight have shimmer and flickering ( flashes on off very rapildy) .
    any idea what's wrong here? what may cause this?
    is it a faulty inverter or tired lamps ?
    is it a capacitor problems in the power supply area?
    any tip or help is highly appreciated and thanks in advance
    i've the service manual for this model which has the power supply but not the inverter circuit and i can attach it if any one needs it or not available here , didn't check for it.
    please help
    Kind Regards
  • Poziom 12  
    sawwa7 napisał:
    Hi all colleagues
    i've got this LG 575LE based on Chassis CL-18 dead after repairing power supply i've got stable 5.1V and all the 4 BA033 are getting 5.1V and produce the 3.3V and everything is ok ,the main fuse in the inverter circuit was alo open and after replacing it and powering the monitor up , the monitor power up normally and has OSD and the picture is normal , the only problem now is the backlight have shimmer and flickering ( flashes on off very rapildy) .
    any idea what's wrong here? what may cause this?
    is it a faulty inverter or tired lamps ?
    is it a capacitor problems in the power supply area?
    any tip or help is highly appreciated and thanks in advance
    i've the service manual for this model which has the power supply but not the inverter circuit and i can attach it if any one needs it or not available here , didn't check for it.
    please help
    Kind Regards

    Hi again
    i just want to add some info may getting some help
    i don't have a power supply problem here as all supply rails are ok
    i'm using atx external power supply to power up this monitor (12V) as i don't have the power adaptor , the output from the DC/DC converter is exactly 5.1V and i have 12V on the inverter board .
    the monitor power up and the power led is green , the supply to inverter backlight driver is 12V , and the inverter board is based on OZ960 chip ,the inverter transformers not open and sound identical when measuring the resistance of both secondary sides ( 1K ohm) and the OSD is comming and i have a good picture if the VGA cable is connected to PC .
    the only problem i have is blinking backlight , not the power led .
    the backlight sounds like if its on/off rapidly .
    has any one come across this fault before ?
    is it an inverter , backlight or power supply problem?
    please help if u can
    thanks in advance
    Kind Regards
  • Poziom 12  
    Hi all colleagues
    want to feedback about solving this problem :)
    i've checked the backlight feedback circuit as testing the lamps one at a time proved that all lamps are working fine and also the inverter transformers also good .
    the backlight feedback circuit consists of D3,D4 and resistors :
    R7 = 470 Ohm
    R12 = 470 Ohm
    R17 = 1K Ohm
    R18 = 1K Ohm
    and the lower lamps consists of D8,D9 and resitors :
    R21 = 470 Ohm
    R22 = 330 Ohm which should be identical to R21 and should = 470 Ohm
    R23 = 1K Ohm
    R24 = 1K Ohm
    changing R22 value from 330 Ohm to 470 Ohm restored normal operation and the monitor now working fine without any backlight flicker .
  • Poziom 12  
    sawwa7 napisał:
    Hi all colleagues
    want to feedback about solving this problem :)
    i've checked the backlight feedback circuit as testing the lamps one at a time proved that all lamps are working fine and also the inverter transformers also good .
    the backlight feedback circuit consists of D3,D4 and resistors :
    R7 = 470 Ohm
    R12 = 470 Ohm
    R17 = 1K Ohm
    R18 = 1K Ohm
    and the lower lamps consists of D8,D9 and resitors :
    R21 = 470 Ohm
    R22 = 330 Ohm which should be identical to R21 and should = 470 Ohm
    R23 = 1K Ohm
    R24 = 1K Ohm
    changing R22 value from 330 Ohm to 470 Ohm restored normal operation and the monitor now working fine without any backlight flicker .


    Hi all colleagues
    unfortunately the monitor worked perfect for more than 6 hours and then returned back to the same fault ( flickering backlight ) ,but now i noticed that the scalar chip GMZAN1 is getting hot !!
    now , is that a retired lamps ? or does the scalar chip has something to do with this fault?
    if any one has an idea , please advice as soon as you can
    i think i'll return the monitor back to the customer today , repaired or unrepaired
    Kind Regards