I just wanted to post about a Westinghouse LCM 17v8 I just fixed. In the end, it was due to two wires that had come loose from the CCFL bulbs! The key symptom was a "rustling" sound coming not from the power supply, but from the corners where the CCFL wires go into the panel, indicating arcing there. Read on for the complete story 
A friend had a Westinghouse LCM 17v8 manufactured in 2006 that failed just recently (February 2010). It would power on, show the display fine for a few seconds, then go blank. Power light would stay green, and you could faintly still see the image if you had a room light shining on the screen. Powering off then back on would show the display for a few seconds again. Sometimes powering on would just flash the display once every several seconds, making a rustling noise.
After reading about bad capacitors being common, I opened it up and examined them. I couldn't see any bulging or discoloration at all, but I went ahead and tried swapping some of them out. No change in symptoms.
Running it again while open, it was almost as if the rustling noise wasn't coming from the power supply. It is hard to tell with switchers, because it seems like all sorts of components can emit noise, not just the transformer. I figured maybe the CCFL bulbs were old, and that perhaps they were drawing too much current, which the inverter was detecting after a few seconds. I tried adjusting one of the resistors connected to the sense pin, but no luck.
Nearing defeat, I listened again and was sure this time that the rustling was coming from the area where the wires connect to the CCFL bulbs, not the power supply. There was definitely some kind of arcing there. This would require opening the LCD panel completely. Since I had exhausted other options, I figured what the hell, as I'd get some experience opening an LCD panel.
I removed the metal rim from the front. This of course was stuck to that clear "do not touch" sticker that goes onto the LCD connector board. It kept wanting to drag those delicate ribbon cables from the LCD, so I had to very carefully remove it. I'd recommend removing this label before removing the metal rim. Once the rim is removed, the LCD can swing out, using the ribbons connecting to it as a (very easily breakable) hinge, so keep it held in at the left and right edges. I the laid it face-down on a bed, unscrewed the processor board and LCD connecting board, carefully swung them up, then lifted the backlight assembly up, leaving the LCD and connector laying there.
Sure enough, one of the backlight wires popped out at this point. I removed the front black edge piece, then slid the CCFL bulbs out of that one corner (they're held by a metal L-clip). Getting the small soft cover off the ends wasn't easy, due to the thick wires plus heat-shrink tubing over them. I re-soldered the wire, went ahead and re-soldered the other wire to the other bulb as well, put it all back together, being very careful not to get any dust or hairs between the backlight and the LCD. I just used a wad of everyday tissue, and looked at reflected light to see whether anything was still on the various layers behind the LCD as I put them back on.
It powered up well, but still flickered occasionally, and I could still hear some rustling from the other corner. Argh! I could smell plastic burning, and realized a wire had come loose from the other corner as well. So repeat the above tedious process, being sure not to get dust or hairs in the backlight assembly again. Either someone soldered these in badly, or something else weakened the wires a lot. One thing's for sure, I'm going to recommend my friend not run this with the brightness above about 40, so as to reduce the (average) current and heating of the bulbs.
I'm still expecting another wire to fail, but I've got it all back together (missing one screw though) and testing now for a few hours. I can still smeel the burned plastic from before, but I'm hoping that's just residue rather than a new issue. I'm also very amateur in electronics repair and have hardly any equipment. I got lucky here, as it could have easily been something beyond my ability to diagnose.
This forum is appreciated, as it gave me ideas and kept my hope up.
A friend had a Westinghouse LCM 17v8 manufactured in 2006 that failed just recently (February 2010). It would power on, show the display fine for a few seconds, then go blank. Power light would stay green, and you could faintly still see the image if you had a room light shining on the screen. Powering off then back on would show the display for a few seconds again. Sometimes powering on would just flash the display once every several seconds, making a rustling noise.
After reading about bad capacitors being common, I opened it up and examined them. I couldn't see any bulging or discoloration at all, but I went ahead and tried swapping some of them out. No change in symptoms.
Running it again while open, it was almost as if the rustling noise wasn't coming from the power supply. It is hard to tell with switchers, because it seems like all sorts of components can emit noise, not just the transformer. I figured maybe the CCFL bulbs were old, and that perhaps they were drawing too much current, which the inverter was detecting after a few seconds. I tried adjusting one of the resistors connected to the sense pin, but no luck.
Nearing defeat, I listened again and was sure this time that the rustling was coming from the area where the wires connect to the CCFL bulbs, not the power supply. There was definitely some kind of arcing there. This would require opening the LCD panel completely. Since I had exhausted other options, I figured what the hell, as I'd get some experience opening an LCD panel.
I removed the metal rim from the front. This of course was stuck to that clear "do not touch" sticker that goes onto the LCD connector board. It kept wanting to drag those delicate ribbon cables from the LCD, so I had to very carefully remove it. I'd recommend removing this label before removing the metal rim. Once the rim is removed, the LCD can swing out, using the ribbons connecting to it as a (very easily breakable) hinge, so keep it held in at the left and right edges. I the laid it face-down on a bed, unscrewed the processor board and LCD connecting board, carefully swung them up, then lifted the backlight assembly up, leaving the LCD and connector laying there.
Sure enough, one of the backlight wires popped out at this point. I removed the front black edge piece, then slid the CCFL bulbs out of that one corner (they're held by a metal L-clip). Getting the small soft cover off the ends wasn't easy, due to the thick wires plus heat-shrink tubing over them. I re-soldered the wire, went ahead and re-soldered the other wire to the other bulb as well, put it all back together, being very careful not to get any dust or hairs between the backlight and the LCD. I just used a wad of everyday tissue, and looked at reflected light to see whether anything was still on the various layers behind the LCD as I put them back on.
It powered up well, but still flickered occasionally, and I could still hear some rustling from the other corner. Argh! I could smell plastic burning, and realized a wire had come loose from the other corner as well. So repeat the above tedious process, being sure not to get dust or hairs in the backlight assembly again. Either someone soldered these in badly, or something else weakened the wires a lot. One thing's for sure, I'm going to recommend my friend not run this with the brightness above about 40, so as to reduce the (average) current and heating of the bulbs.
I'm still expecting another wire to fail, but I've got it all back together (missing one screw though) and testing now for a few hours. I can still smeel the burned plastic from before, but I'm hoping that's just residue rather than a new issue. I'm also very amateur in electronics repair and have hardly any equipment. I got lucky here, as it could have easily been something beyond my ability to diagnose.
This forum is appreciated, as it gave me ideas and kept my hope up.
Comment