LG 50UH5530 - Power supply - 168P-L5L01F-W0

[anupkg1985]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

Q407 emitter is connected to ground.

My bad, it's connected to collector of Q407. Cap 429, negative is connected to Emmiter and positive is connected to Collector pins.

[R_J]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

The emitter of Q407 is connected to ground, C429 positive is connected to D407 and to Q407 through a 10Ω resistor. I can't follow where D407 goes.

[anupkg1985]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

If I connect-ve of LED strings to chasis or ground, led lights up however it goes on and off with same rhythm of clicking sound. Not sure if connecting negative terminal of LEDs to ground is good idea. But looks likes something is bringing down the PSU and that's the noise of clicking.

[Davi.p]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

The only hypothesies i can make, zd12 act as voltage regulator for U1 and must be repopulated, u1 shuts down for ovp, check also its datasheet. But i checked DS and on supic pin there is already internal regulator, so two primary side small el. caps are suspected check them for capacity/esr.

[anupkg1985]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

UPDATE - I just found that resistor R41 rated for 10ohm was actually reading 13K, after replacing that one PSU is stable now. No more clicking noise so PFC is working fine. However there is still no voltage on LED terminals. Backlights doesn’t light up. I tried to get initial reading while plugging tv into power however no voltage at all. It always remains 0V when measured across + and - terminals of LED connector. However when I measure GND (chasis) to + LED, it measures around 100V and GND to -ve LED it is around 60V. Not sure whats wrong and why LED strings are not lighting up.

[Davi.p]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

Bad led strips

[anupkg1985]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

Pretty much aligned with you guys, I tested led strips with LED tester and found that the strips are drawing 0.28A current where the board output is 0.35A, so I would try replacing the entire strips and will update again. Meanwhile I found another bad resistor on secondary side R457 (47 ohms) but it was reading around 3.6K ohms. It's on the VCC line of the U2, however replacing it doesn't change anything so will give a shot by replacing strips. Thanks @R_J and @Davi.p for your support.

[anupkg1985]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

I changed to new strip however no backlight. Not sure whats wrong with driver circuit. Anybody any pointers?

[Davi.p]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

OMG!.. R41 & R457 how are marked?

[anupkg1985]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

I have already changed R457 as it was bad (comment#27) same for R41. Both of them were reading high than there ratings.

[R_J]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

Where does R457 connect?

[anupkg1985]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

It ultimately connects to U2 vcc pin 9, where I'm getting 1.3volts.

[R_J]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

I would thing that is a bit low for a vcc, likey bore like 12v. Check the voltage on R407 (both sides) and R21

A closser look and I think R457 connects to +13.2V

[Davi.p]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

You can't answer my question?

[anupkg1985]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

On R457 its 13v then gets droped on each resistor and ultimately on R407 it is 1.7volts.

[R_J]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

so R407 has the same voltage on both sides so I can only assume U2 is defective. or If you remove R407, does the voltage on R21 come up to 12v?

[anupkg1985]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

Yes, removing R407 makes it back to 13v, so the U2 is bad?

[R_J]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

C6 is the only other component on that line but I doubt it is bad, so most likely U2 is bad.
Just for the heck of it, is R21 ok and not high in value?

[anupkg1985]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

R21 is reading as 1.2ohms and removing c2 doesn't change anything. Voltage drops back to 1.7V if resistor R407 is connected back. Is it worth replacing U2?

[nomoresonys]

Re: LG 50UH5530 - Power supply - 168P-L5L01F-W0

R21 is reading as 1.2ohms and removing c2 doesn't change anything. Voltage drops back to 1.7V if resistor R407 is connected back. Is it worth replacing U2?

sure, switch it out to rule it out.