Question about LG L1951S-SN (Silver, Black) (Black, Silver) 19" LCD Monitor

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Hello, I am trying to fix the monitor LG L1951s that does not power on, I found the 68uF*450V capacitor bad, replaced this one but problem ramains. I have measured most of the componets on the power board and they seem to be fine; however for some reason after the high frequency transformer (secondary) on the power supply, I do not get any voltaje and the FAN7601 which is a current mode PWM controller it does not have voltaje either, this IC seems to be fed by the secondary of this transformer too , could be the transformer the one that is damaged? or is there is something else I need to check?, I would really appreciate some inputs on the solutions, thanks

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The 68UF 450 is for the primay smps driving side, are you getting about 160vdc on that cap?
The PWM IC get the kick start DC voltage from the main bridge rectifier thorough a bunch of high resistance resistor to drop the 160vdc down to aboit 15vdc, once the PWM IC start working, one the winding will be the supplying the voltage to the IC to keep it running. If the DC output side detect short cirsuits (drawing too much current) it will go into shutdown, you need to find out if the inverter circuits has short circuits. The 5vdc and the 12~18vdc power supply will be running the minute you plug it in, you can solder in a 12v bulb at the DC output that feeds the inverter circuits (you can solder it directly on the DC filter caps for the 12~18 VDC filter caps of the inverter circuits). See application notes how this IC is used.
http://www.fairchildsemi.com/an/AN/AN-4129.pdf
http://www.fairchildsemi.com/ds/FA%2FFAN7601.pdf

No blown MOSFET on the primay side?
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide

http://s807.photobucket.com/home/budm/allalbums

http://en.wikipedia.org/wiki/Capacitor_plague

Posted on Aug 23, 2010

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If you are going to DIY and have proper tools and know safety precaution then please read on:
Most common failures in the LCD monitors are bad capacitors (bulging top/seal or leaking) in the power supply (they should be replaced in a set), blown fuses; poor solder joints, failed inverter circuits (blown fuse, shorted transistors, shorted/open transformers), bad lamps (poor solder connections or worn out lamps). You will need to open it up and inspect the inside, see example of failed LG and other monitors to get some ideas what to look for: http://s807.photobucket.com/albums/yy352/budm/
Post back what you see inside so we can guide you further and it will help out other people in the future also.

Basic LCD monitor troubleshooting guide:
http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide

http://en.wikipedia.org/wiki/Capacitor_plague

Learn about bad caps: Capacitors kit: http://lcdalternatives.auctivacommerce.com/ he can make you a set of caps for you.

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http://en.wikipedia.org/wiki/Capacitor_plague
Please post back what you find

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