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Old 06-18-2010, 02:58 PM   #1
Scenic
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Default LG L1952HQ LCD -> no backlight

got this LG L1952HQ-SF 19" LCD dirt cheap (10 euros / about 12.36US$)

seller said it would turn on and show a picture but will immediately turn off again. within that split second the picture was visible without distortion.

easy enough (or so i thought).. got it here now.. turns on, shows no-signal message and immediately turns the backlight off, but stays running otherwise. along with the backlight turning off i also get a "fried electronics smell" out of the back.. ugh..

i actually had to search for the service manual because i tried and tried and couldn't figure out how to open this friggin thing
only found one of the L1953H , but that model seems to be completely identical from what i can tell.. (down to the component level list & the components actually on my L1952HQ PCBs)

Link (reuploaded because the original server was slow as hell (3-10KB/s))
http://bambooz.pytalhost.net/badcaps...ice_manual.pdf

while disassembling i didn't notice anything obvious apart from the serious lack of screws (everything's held together/in place by the outer plastic shell .. just taped into place..)..

well.. at least until i tried unplugging the backlights from the inverter. one of the plugs was seriously stuck in there.. closer look and i found this..:





after some careful fiddling around with needle-nose pliers..



for some reason the plug started arcing till it melted all the plastic around it, and then shorted out against the tiny metal pole (which is grounded) that helps to support the socket onto the PCB.




otherwise this monitor is in damn good shape.. barely any dust, no scratches.. even the infamous Samxon GF caps on the powersupply/inverter board were all still (visibly) OK and not bulging at all.. o_O
strange.. that's just like finding non-bloating fuhjyyus

http://bambooz.pytalhost.net/badcaps...u-inverter.jpg

gonna replace both the socket and the plug and resolder the board while i'm at it (i hate the leadfree RoHS bullsh*t solder)..
want to replace the caps too just so i don't have to open it up again in a month or so .. especially since this thing is a painus in the anus to take apart without cracking the case or leaving pry-marks everywhere..

have to order some caps cause i basically have none of the required values at hand.. i think i'm gonna go with Panny FC .. heat wise..
or i'll order caps from big pope for the first time ever

oh and yeah.. on this model, they also left out the pi-filter/coil (?) L201 for the 12V output of the powersupply which feeds the backlight. has just a jumperwire there like it's mentioned on another LG LCD thread where they also left it out..
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Old 06-19-2010, 01:06 PM   #2
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Default Re: LG L1952HQ LCD -> no backlight

well.. thought this would be an easy fix... spoke too soon.
seems like the plug was the main reason why it went flaky, but after i relpaced both the plug and the socket, it still shut down the backlight. damnit.

after some examination it turned out that the previous owner probably bashed the LCD on top "cause it works when i do this".. found one CCFL tube of the top pair being cracked

other than that, it seems to work fine when i connect a differnt pair of CCFLs from another LCD with a cracked screen.
time for some CCFL surgery i guess..

on a side note, the panel used in this monitor (an LG-Philips LM190E03) has what i call "easy access" CCFLs. there's a small screw in the corner of the LCD screwing into a black plastic bracket in there which also acts as a guide for the CCFL cables. once you undo that screw and carefully (!!!) pull at the wires going to the CCFLs, the whole metal U-bracket with the CCFL pair should slide out to the side.
pretty neat..





and the cracked one of the upper pair
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Old 06-19-2010, 11:24 PM   #3
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Default Re: LG L1952HQ LCD -> no backlight

it's now 7:25am, i still haven't slept yet *yawn*.. but the monitor is working fine again
replaced the cracked CCFL with one out of a cracked panel. was a little bit shorter than the original, but i fiddled around a bit and got it in there.
partly reassembled, power on and we have life


backlight doesn't turn off, everything's evenly lit (my cam has a little chipped part on the lens, so there's always a darker spot in the lower right of those photos, rest is reflection), no hissing or other strange noises coming from the PSU.

haven't replaced the caps yet, but i've added a pi filter coil for the 12V rail (where the jumperwire used to be). don't really know if it helps but it didn't release the magic smoke either.. coil is barely hand-warm after leaving the monitor on for 30mins
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Old 06-20-2010, 06:26 AM   #4
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Default Re: LG L1952HQ LCD -> no backlight

Congrats, I just recapped another L1917S to rid it of blown Samxon caps.
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Old 06-29-2010, 05:15 AM   #5
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Default Re: LG L1952HQ LCD -> no backlight

Entirely recapped with Panasonic FC's. All done..


now just to get rid of this crappy TN-panel monitor (-> ebay) and get one with a PVA or MVA Panel like my main LCD

if that's all TN has to offer, i'm not impressed.
i kept fiddling around with the contrast, brightness, gamma, dynamic contrast, flatron-engine and whatnot.. the picture ALWAYS looke like sh*t no matter what i do.. (compared to my MVA Panel Belinea 101910 right next to it.)

just about the ONLY thing that's slightly better than my Belinea is the response time.. doesn't help much if the picture looks like crap though
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