Philips 52PFL5605H LED TV with FSP190-3MS01 power supply board.
No power at all, 3.3V standby missing.
0V on the secondary, 325V on the primary cap.
So we start by looking at the 3.3V controller IC, part number STR-A6069H.
325V on the D/ST pin, but the IC is not switching. VCC pin voltage is oscillating between 9V and 13V. BR pin is oscillating between 1.8V and 2V.
Looking at the datasheet, we can see that the brown-out threshold on BR pin is 4.8V, and we have a voltage much lower than that. Checking the typical application circuit, we can see that this voltage comes from a resistor voltage divider. Either one of the resistor is bad, or the IC is bad.
Following the traces on the backside of the motherboard, we encounter a set of resistors and start measuring them. It turns out that one of them, R106, has gone bad. Its color code indicates a 2.2 megaohms resistor, but it is measuring around 50 megaohms. After replacing it with 2*1 megaohms, the 3.3V standby is back and the TV is fully working again. BR pin is now a little above 6V.
Took me 2 hours to figure that out because I never suspected this resistor, a small axial resistor which looked perfectly fine.
No power at all, 3.3V standby missing.
0V on the secondary, 325V on the primary cap.
So we start by looking at the 3.3V controller IC, part number STR-A6069H.
325V on the D/ST pin, but the IC is not switching. VCC pin voltage is oscillating between 9V and 13V. BR pin is oscillating between 1.8V and 2V.
Looking at the datasheet, we can see that the brown-out threshold on BR pin is 4.8V, and we have a voltage much lower than that. Checking the typical application circuit, we can see that this voltage comes from a resistor voltage divider. Either one of the resistor is bad, or the IC is bad.
Following the traces on the backside of the motherboard, we encounter a set of resistors and start measuring them. It turns out that one of them, R106, has gone bad. Its color code indicates a 2.2 megaohms resistor, but it is measuring around 50 megaohms. After replacing it with 2*1 megaohms, the 3.3V standby is back and the TV is fully working again. BR pin is now a little above 6V.
Took me 2 hours to figure that out because I never suspected this resistor, a small axial resistor which looked perfectly fine.
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