Strange LCD repair outcome
in [Repair]
|
Prev: ~~~~~~~~~~~~~~ ARTHRITIS FOUNDATION ~~~~~~~~~~~~~~
Next: schematic diagram Harrison "K-4000" (K4000) MK-II 2x1000W wanted
From: pedro on 26 Dec 2009 20:57 I normally repair LCD monitors which are heading for landfill, and they are turned over to needy/worthy groups (usually replacing olde CRTs). Almost always, repairs are either "recap SMPS" or "replace inverter transistors", and the hardest part is getting the case apart. Recently one Samsung 943NWX - presented as "dead" - had an odd outcome. Replaced the bulging electros in the PSU and the unit came to life, but with a dominant pink tinge to the entire screen area. Normally I would ascribe this to backlight end-of-life, but three things contradict this diagnosis. Firstly, hitting the menu button with no video drive gives a small display "Test OK" (or similar) text on a background which is white, so backlight colouration is unlikely. Ditto if the menu system is fired up when a video signal is present - pink screen but the menu b/g is pure white. Clearly the VGA input is being incorrectly processed. Finally, the donor has confirmed that it was white before failure. Has anyone experienced the video processor taking a hit when the SMPS goes west with faulty caps? Clearly the unit doesn't warrant pursuing a video chip replacement, and thereare no signs of distress on the video board.
From: Sylvia Else on 26 Dec 2009 21:26 pedro wrote: > I normally repair LCD monitors which are heading for landfill, and > they are turned over to needy/worthy groups (usually replacing olde > CRTs). Almost always, repairs are either "recap SMPS" or "replace > inverter transistors", and the hardest part is getting the case apart. > > Recently one Samsung 943NWX - presented as "dead" - had an odd > outcome. Replaced the bulging electros in the PSU and the unit came > to life, but with a dominant pink tinge to the entire screen area. > Normally I would ascribe this to backlight end-of-life, but three > things contradict this diagnosis. Firstly, hitting the menu button > with no video drive gives a small display "Test OK" (or similar) text > on a background which is white, so backlight colouration is unlikely. > Ditto if the menu system is fired up when a video signal is present - > pink screen but the menu b/g is pure white. Clearly the VGA input is > being incorrectly processed. Finally, the donor has confirmed that it > was white before failure. > > Has anyone experienced the video processor taking a hit when the SMPS > goes west with faulty caps? Clearly the unit doesn't warrant pursuing > a video chip replacement, and thereare no signs of distress on the > video board. Some LCD monitors have colour temperature settings embedded somewhere in their menu system. I can certainly get my Philips monitor to emulate the behaviour you describe. Sylvia.
From: Jamie on 27 Dec 2009 13:04 Meat Plow wrote: > On Sun, 27 Dec 2009 09:57:11 +0800, pedro <me(a)home.net>wrote: > > >>I normally repair LCD monitors which are heading for landfill, and >>they are turned over to needy/worthy groups (usually replacing olde >>CRTs). Almost always, repairs are either "recap SMPS" or "replace >>inverter transistors", and the hardest part is getting the case apart. >> >>Recently one Samsung 943NWX - presented as "dead" - had an odd >>outcome. Replaced the bulging electros in the PSU and the unit came >>to life, but with a dominant pink tinge to the entire screen area. >>Normally I would ascribe this to backlight end-of-life, but three >>things contradict this diagnosis. Firstly, hitting the menu button >>with no video drive gives a small display "Test OK" (or similar) text >>on a background which is white, so backlight colouration is unlikely. >>Ditto if the menu system is fired up when a video signal is present - >>pink screen but the menu b/g is pure white. Clearly the VGA input is >>being incorrectly processed. Finally, the donor has confirmed that it >>was white before failure. >> >>Has anyone experienced the video processor taking a hit when the SMPS >>goes west with faulty caps? Clearly the unit doesn't warrant pursuing >>a video chip replacement, and thereare no signs of distress on the >>video board. > > > Maybe something you did while servicing? I wouldn't look for faulty > caps in the smps to cause anything but a fail of the smps. I know some one that handed me a power supply board from a LCD TV that needed a cap replaced. This was a known problem with this unit. I had to order the cap because of it's size.. I replaced the cap, and then handed the board back to the owner... He put it in and while doing so, pinched the small mylar ribbon going to the LCD panel it self. End of story. The cost of getting a replacement ribbon and what was already put in was more than a new TV. This was a small unit.. The morrow of the story is, while trying to recover home entertainment equipment that is valued very close to a repair job, is gambling! You some times lose!
From: Baron on 27 Dec 2009 15:53 Meat Plow Inscribed thus: > On Sun, 27 Dec 2009 09:57:11 +0800, pedro <me(a)home.net>wrote: > >>I normally repair LCD monitors which are heading for landfill, and >>they are turned over to needy/worthy groups (usually replacing olde >>CRTs). Almost always, repairs are either "recap SMPS" or "replace >>inverter transistors", and the hardest part is getting the case apart. >> >>Recently one Samsung 943NWX - presented as "dead" - had an odd >>outcome. Replaced the bulging electros in the PSU and the unit came >>to life, but with a dominant pink tinge to the entire screen area. >>Normally I would ascribe this to backlight end-of-life, but three >>things contradict this diagnosis. Firstly, hitting the menu button >>with no video drive gives a small display "Test OK" (or similar) text >>on a background which is white, so backlight colouration is unlikely. >>Ditto if the menu system is fired up when a video signal is present - >>pink screen but the menu b/g is pure white. Clearly the VGA input is >>being incorrectly processed. Finally, the donor has confirmed that it >>was white before failure. >> >>Has anyone experienced the video processor taking a hit when the SMPS >>goes west with faulty caps? Clearly the unit doesn't warrant pursuing >>a video chip replacement, and thereare no signs of distress on the >>video board. > > Maybe something you did while servicing? I wouldn't look for faulty > caps in the smps to cause anything but a fail of the smps. A possible cause is the user settings got cleared in the flash chip whilst replacing components. -- Best Regards: Baron.
From: Arfa Daily on 27 Dec 2009 20:10
<snip> >>was white before failure. >> >>Has anyone experienced the video processor taking a hit when the SMPS >>goes west with faulty caps? Clearly the unit doesn't warrant pursuing >>a video chip replacement, and thereare no signs of distress on the >>video board. > > Maybe something you did while servicing? I wouldn't look for faulty > caps in the smps to cause anything but a fail of the smps. For the most part, I would agree with that, but I have had a few cases of cheapo DVD players, where a bulging secondary side cap, has caused the rail which is used as the regulation reference (often the 5V) to drop, which has resulted in the supply trying to compensate by widening the drive pulses, which has in turn resulted in the 12V rail rising, which has then led to other circuitry getting twatted ... Arfa |