Philips Plasma with faulty PS-424-PH PSU (no Vs, Ve, D5v)
Good day fellow cappers, got a pretty complex project on my hands here, but I feel like I'm getting pretty close, so let's tinker this together: there's this LARGE Philips TV which has power supply issues. The power board is a Samsung ps-424-ph which has no Vs, Ve and most imporantly, no D5v and D3V3 outputs either. The biggest issue is that I can't find a schematic for it, only the repair guide which I've attached for your convenience.
You plug the board in (on its own, without anything else attached), the two relays click, stay like that for a few seconds and then switch off again. The two large caps charge up to about 350v, but just from that initial pulse until the relays cut off the power going to the rectifier, at which point they slowly begin to discharge (I can even drain them manually with a lightbulb and it makes no difference).
The LED on the daughter-board on the left side of the PSU returns an error code, namely a 13-blink code, indicating missing D5V and sure enough, I get nothing out of both the D5V output and the 3v output. Funny thing is that I also located another problem: two shorted MOSFETs (Q8022 and Q8020) that drive the large Ve-Vs transformer (notice I've already removed one of them) and of course a blown fuse (F8007). The blink code says nothing about that, though it could be because it's a shorter blink code that the 5v one and the board displays the longer ones first when there's more than one error. There's no doubt Ve-Vs are dead due to those busted FETs, but they're pretty expensive to replace and I don't want to waste money on them only to discover a truck-load of other dead components, so I first want to tackle the faulty D5V bus. I managed to track down the problem all the way to the primary side, now hopefully I'll be able to explain this well enough so we don't get lost, since this is one of those double-sided boards to make matters worse. To put it simply, IC8017 has no VCC. IC8017 is a 1207A (supposedly an NCP1207A by its full name, according to the datsheet). This IC drives Q8016, which in turn drives transformer T8002, which is fed into the secondary side - standard SMPS, if you think about it (I've taken a close-up of that general area). The thing is, VCC is supposed to come through C8069, but I get nothing on either side of that cap. Following the trace from the cap (which acts as a rectifier in this case), I can see it comes from an auxiliary winding of T8002. This is where it gets confusing and complicated as F, especially with no schematic: it seems to me this AUX winding (the bottom 2 pins of T8002) has no way to run without those two FETs, since I see another trace running to a capacitor in that general direction (C8067 visible at the very top of the last picture) which goes to the first pin of the transformer. Could that be why I'm not gettig squat out of that transformer, or am I wrong ? The repair guide doesn't talk about this, so I'm wondering how T8002 even works :| All other fuses are OK and I couldn't find any shorts in any of the major components....any tips or at least a schematic ? Feel free to ask for any further info I might've missed. Cheers.
You plug the board in (on its own, without anything else attached), the two relays click, stay like that for a few seconds and then switch off again. The two large caps charge up to about 350v, but just from that initial pulse until the relays cut off the power going to the rectifier, at which point they slowly begin to discharge (I can even drain them manually with a lightbulb and it makes no difference).
The LED on the daughter-board on the left side of the PSU returns an error code, namely a 13-blink code, indicating missing D5V and sure enough, I get nothing out of both the D5V output and the 3v output. Funny thing is that I also located another problem: two shorted MOSFETs (Q8022 and Q8020) that drive the large Ve-Vs transformer (notice I've already removed one of them) and of course a blown fuse (F8007). The blink code says nothing about that, though it could be because it's a shorter blink code that the 5v one and the board displays the longer ones first when there's more than one error. There's no doubt Ve-Vs are dead due to those busted FETs, but they're pretty expensive to replace and I don't want to waste money on them only to discover a truck-load of other dead components, so I first want to tackle the faulty D5V bus. I managed to track down the problem all the way to the primary side, now hopefully I'll be able to explain this well enough so we don't get lost, since this is one of those double-sided boards to make matters worse. To put it simply, IC8017 has no VCC. IC8017 is a 1207A (supposedly an NCP1207A by its full name, according to the datsheet). This IC drives Q8016, which in turn drives transformer T8002, which is fed into the secondary side - standard SMPS, if you think about it (I've taken a close-up of that general area). The thing is, VCC is supposed to come through C8069, but I get nothing on either side of that cap. Following the trace from the cap (which acts as a rectifier in this case), I can see it comes from an auxiliary winding of T8002. This is where it gets confusing and complicated as F, especially with no schematic: it seems to me this AUX winding (the bottom 2 pins of T8002) has no way to run without those two FETs, since I see another trace running to a capacitor in that general direction (C8067 visible at the very top of the last picture) which goes to the first pin of the transformer. Could that be why I'm not gettig squat out of that transformer, or am I wrong ? The repair guide doesn't talk about this, so I'm wondering how T8002 even works :| All other fuses are OK and I couldn't find any shorts in any of the major components....any tips or at least a schematic ? Feel free to ask for any further info I might've missed. Cheers.
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