LG 32le5300 with bad power supply (help)
Good day folks. Hope you can provide a bit of help on this topic, as I'm stuck as hell right now ! Got an LG 32le5300 which is driving me nuts - can't possibly figure out what's wrong with its power supply ! 
Here's the story: when I first got it, it had a blown fuse and one of the blue disk capacitors near the heatsink in the bottom right of my first pic (the one with the 2 transistors and the diode) was blown apart. I replaced both of those caps for good measure (221K if I remember correctly), replaced the fuse, plugged it in (with a lightbulb in series of course, being the tech-savvy guy that I believe I am 
), and it glowed bright and steady....well damn >_> The area around those transistors also made sort of a whizzing sound. I obviously pulled the plug before anything could go wrong and continued my searches.
It was time to check for shorts: none of the transistors, nor any diodes (including the bridge rectifier itself) showed any dead shorts. I even went out of my way to replace those 2 transistors and the TO-220 diode, but the result was the same: the light glowed brightly and steadily - would've definitely blown the fuse if I were to plug it straight in, that's what I mean.
The careful observer might notice that I pulled out some jumpers at one end (including the fuse in the middle, which was NOT blown originally) - by that, what I tried to do was isolate the fault: see whether the short is in the PFC circuit or the switching part that comes after that and I'm pretty sure it's in the PFC, since even after disconnecting that fuse and any other jumpers connecting the HV side to the rest of the board, the bulb still comes on and I can hear that faint buzz coming from that general area. Interestingly, if I remove the transistors and diode entirely, the bulb goes off after a brief moment (after the reservoir caps charge up) - it's only when that PFC IC receives power and starts to switch the transistors that trouble occurs (that is, when I connect the ON/OFF pin to 3.5Vstby, which operates normally by the way). That STBY circuit is a bit of a freak: the STBY part of the board uses the negative leg of the main bridge rectifier, but has its own series of diodes for "+" placed before the relay so they're always on. That relay closes when you apply 3.5v to ON/OFF and apart from the relay, that also sends power to the switching ICs (all 3 of them: the PFC one, plus the two others for the two transformers). The only thing left to replace would be the PFC IC itself, but it's expensive as all hell and I don't want to spend money on it only to discover it's not that. Checked the majority of the SMD resistors and they're all OK...don't know what else to try ! Haven't taken too many voltage readings, since I can't keep it plugged in for too long, even with the lightbulb. Can a PFC coil go bad to such degree that it would cause a short ? I measured its terminals in pairs of 2 and there doesn't appear to be a short between the main winding and the feedback winding. The board is a PLDC-1901A (it's visible in the bottom left of the first pic). I also took a close-up of the PFC area where I think the fault is.
Here's the story: when I first got it, it had a blown fuse and one of the blue disk capacitors near the heatsink in the bottom right of my first pic (the one with the 2 transistors and the diode) was blown apart. I replaced both of those caps for good measure (221K if I remember correctly), replaced the fuse, plugged it in (with a lightbulb in series of course, being the tech-savvy guy that I believe I am ), and it glowed bright and steady....well damn >_> The area around those transistors also made sort of a whizzing sound. I obviously pulled the plug before anything could go wrong and continued my searches.It was time to check for shorts: none of the transistors, nor any diodes (including the bridge rectifier itself) showed any dead shorts. I even went out of my way to replace those 2 transistors and the TO-220 diode, but the result was the same: the light glowed brightly and steadily - would've definitely blown the fuse if I were to plug it straight in, that's what I mean.
The careful observer might notice that I pulled out some jumpers at one end (including the fuse in the middle, which was NOT blown originally) - by that, what I tried to do was isolate the fault: see whether the short is in the PFC circuit or the switching part that comes after that and I'm pretty sure it's in the PFC, since even after disconnecting that fuse and any other jumpers connecting the HV side to the rest of the board, the bulb still comes on and I can hear that faint buzz coming from that general area. Interestingly, if I remove the transistors and diode entirely, the bulb goes off after a brief moment (after the reservoir caps charge up) - it's only when that PFC IC receives power and starts to switch the transistors that trouble occurs (that is, when I connect the ON/OFF pin to 3.5Vstby, which operates normally by the way). That STBY circuit is a bit of a freak: the STBY part of the board uses the negative leg of the main bridge rectifier, but has its own series of diodes for "+" placed before the relay so they're always on. That relay closes when you apply 3.5v to ON/OFF and apart from the relay, that also sends power to the switching ICs (all 3 of them: the PFC one, plus the two others for the two transformers). The only thing left to replace would be the PFC IC itself, but it's expensive as all hell and I don't want to spend money on it only to discover it's not that. Checked the majority of the SMD resistors and they're all OK...don't know what else to try ! Haven't taken too many voltage readings, since I can't keep it plugged in for too long, even with the lightbulb. Can a PFC coil go bad to such degree that it would cause a short ? I measured its terminals in pairs of 2 and there doesn't appear to be a short between the main winding and the feedback winding. The board is a PLDC-1901A (it's visible in the bottom left of the first pic). I also took a close-up of the PFC area where I think the fault is.
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