Problem with Vestel 17PW20 power supply
Good day folks. I need some advice on this Vestel 17PW20 power supply. I thought it'd be a quick and easy job to repair, especially since apparently it's a common PSU that's known for being faulty, but it's more complicated than I thought and couldn't really get a clear-cut result since different people had different problems which were repaired differently.
Got a TeleTech TV (doesn't really matter-could be anything) which has this 17PW20 power supply in it which doesn't output all of its voltages, hence the TV won't turn on. You plug it in, the blue standby light comes on, but when you switch it on all that happens is the blue LED dims slightly and that's it - no picture and no sound.
I found 3 bulged caps, but merely replacing those didn't get it going. Taking some measurements, not all the power rails come on: on connector PL805 and PL812 at the bottom-right of the schematic (which are like 2 in one, don't know what kind of crack they were smoking when they came up with that labeling system...anyway), the standby 5v is present on pin 12 and so is 3.3v on pins 10 and 11, but that's it: no 12v, no 5v and no 24v for the inverter. Strangely enough, PFC does work and the voltage across the main cap is 380v, so we can assume that section works fine. Looking at that connector, you can see there's another 3.3v bus, different from pins 10 and 11, called VCC_3V3_ON - this one doesn't come on either, so I'm essentially missing all voltages. Moving slightly to the left, we see VCC_3V3_ON comes from IC824 NTGS3446 (IC826 directly above that is missing on my board, so just ignore that part) which generates 3.3v from the 12v line which doesn't come on either. At first, give that is has the word ON in its name, I assumed that VCC_3V3_ON needs to be pulled high to 3.3v (which interestingly enough is present on the other two pins - 10 and 11) to enable the power supply, but the little arrow in the schematic tells us VCC_3V3_ON is an "output" not "input" (like), so it's just one of the voltages that should come on and off with the TV...I THINK.
I replaced C835 thinking perhaps there's something wrong with the switching IC807, but it didn't change anything and I must admit I didn't actually measure pin 13 of IC807 to know whether it's getting power AT ALL...I shall do this tomorrow. I put the power supply back on the TV every time I wanted to measure something, since I didn't feel like figuring out how to "jump-start" it off the TV, so that's why I couldn't access the bottom of the board to measure it until now. However, looking closely at the schematic and doing some further testing, I discovered the supply is supposed to turn on just fine even with nothing attached to it, so bench-testing it without the main board IS possible.
I reflowed (is there a past tense for (re)flow ?
) various joints and components which I thought looked a bit "cold", but no cigar....ok, must definitely measure VCC for IC807 on pin 13. Will keep you posted, but in the meantime, has anyone else here dealt with one of these supplies which was dead like this ? It's so close to being fixed and I can already tell it's going to be something simple like a dried cap or cold joint that I missed. Cheers.
Got a TeleTech TV (doesn't really matter-could be anything) which has this 17PW20 power supply in it which doesn't output all of its voltages, hence the TV won't turn on. You plug it in, the blue standby light comes on, but when you switch it on all that happens is the blue LED dims slightly and that's it - no picture and no sound.
I found 3 bulged caps, but merely replacing those didn't get it going. Taking some measurements, not all the power rails come on: on connector PL805 and PL812 at the bottom-right of the schematic (which are like 2 in one, don't know what kind of crack they were smoking when they came up with that labeling system...anyway), the standby 5v is present on pin 12 and so is 3.3v on pins 10 and 11, but that's it: no 12v, no 5v and no 24v for the inverter. Strangely enough, PFC does work and the voltage across the main cap is 380v, so we can assume that section works fine. Looking at that connector, you can see there's another 3.3v bus, different from pins 10 and 11, called VCC_3V3_ON - this one doesn't come on either, so I'm essentially missing all voltages. Moving slightly to the left, we see VCC_3V3_ON comes from IC824 NTGS3446 (IC826 directly above that is missing on my board, so just ignore that part) which generates 3.3v from the 12v line which doesn't come on either. At first, give that is has the word ON in its name, I assumed that VCC_3V3_ON needs to be pulled high to 3.3v (which interestingly enough is present on the other two pins - 10 and 11) to enable the power supply, but the little arrow in the schematic tells us VCC_3V3_ON is an "output" not "input" (like), so it's just one of the voltages that should come on and off with the TV...I THINK.
I replaced C835 thinking perhaps there's something wrong with the switching IC807, but it didn't change anything and I must admit I didn't actually measure pin 13 of IC807 to know whether it's getting power AT ALL...I shall do this tomorrow. I put the power supply back on the TV every time I wanted to measure something, since I didn't feel like figuring out how to "jump-start" it off the TV, so that's why I couldn't access the bottom of the board to measure it until now. However, looking closely at the schematic and doing some further testing, I discovered the supply is supposed to turn on just fine even with nothing attached to it, so bench-testing it without the main board IS possible.
I reflowed (is there a past tense for (re)flow ?
) various joints and components which I thought looked a bit "cold", but no cigar....ok, must definitely measure VCC for IC807 on pin 13. Will keep you posted, but in the meantime, has anyone else here dealt with one of these supplies which was dead like this ? It's so close to being fixed and I can already tell it's going to be something simple like a dried cap or cold joint that I missed. Cheers.
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