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

[anupkg1985]

Hi, I've got this tv with no power symptoms. In further checking I found that there are no voltages on secondary side of the PSU board. Also main caps has only 165V DC voltage. Could you please let me know where to start on this one? Is there any issue with Q1 or pfc ic?

[R_J]

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

Did you check the F2 fuse?

[anupkg1985]

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

Did you check the F2 fuse?

Yes, fuse is ok. Further checking I found ZD12 is open, not sure the reason. Also can I replace it with different zener as I don't have smd type one. ZD12 shows continuity when checked from both sides, checked off the board.

[R_J]

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

Are you sure Zd12 is open? or is it SHORTED? it seems to be on the vcc line of the main ic, so if it IS open, I suspect the ic has been damaged, if it is shorted You would need to post the number on U1, I suspect ZD12 is about 30v

[anupkg1985]

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

Are you sure Zd12 is open? or is it SHORTED? it seems to be on the vcc line of the main ic, so if it IS open, I suspect the ic has been damaged, if it is shorted You would need to post the number on U1, I suspect ZD12 is about 30v

My bad! Zd12 is shorted and not open. U1 IC is TEA1716T.

[anupkg1985]

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

I just tested the board by removing ZD12, there is around 395v on main caps however there is ticking sound from transformer I believe. Also the voltage on main cap is fluctuating from 395 to 400volts. Voltage on c14 reads between 11 to 16 volts.

[R_J]

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

The main cap voltage means the pfc circuit is working, Do you have any of the 12.2V secondary voltage?
If not I would check for a shorted diode in the secondary. The ticking may be normal If you have your secondary voltages but the power supply is unloaded.

[anupkg1985]

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

Yes there is voltage on secondary 12.5v which is bit fluctuating as well as there voltgaes present on caps on secondary side except C15 which is 50v cap. Also there is very fast fluctuating voltage on Q3 gate however on Q2 and Q1 its steady 395v and 165v respectively.

Could not find any bad/ shorted diode on secondary.

[R_J]

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

It could have been just the shorted Zd12 zener, I suspect the rest of the power supply is ok.

[anupkg1985]

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

When all boards connected, tv doesn't power on. Power indicator just blinks and everything resets.

[R_J]

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

Check F3 fuse, Also check the voltage on this fuse. It should be around 100V.
You can't check Q3 gate voltage, you would need to scope the drive signal which is likely around 100kHz

[anupkg1985]

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

F3 is ok and voltage on it is around 97V. Also there was issue with 3 leds which I replaced with new led, not the entire strip. However it doesn't power on as well as leds strips are off. I tested strips with LED tester and looks good.

[anupkg1985]

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

I'm getting around 100v on +terminal of the led connector however voltage is stable on -ve terminal. Its jumping fro. 0 to 60v when measure against the chasis. What could be wrong with led driver?

[R_J]

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

I suspect you have a problem with the led's in the panel, a led tester will not test them at there rated current so when they try and light from the power supply they trip the protection circuit.

[anupkg1985]

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

Ok, but I'm curious why there is no voltage on c15 as mentioned in comment#8? Is there any to force start the led driver or taking out from protection mode?

[R_J]

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

C15 is not even populated, I think you mean C428/9? One side is ground but I can't trace where the positive connects
There are three separate driver circuits and I suspect they monitor Over voltage, Under voltage as well as current, these are not simple circuits to bypass
What is the number on U2?
Check if R21 is ok, looks like it is a less than 1Ω resistor, maybe ic's vcc?

[anupkg1985]

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

Please find the marked cap in attached snap, I'm not getting any voltage on it. It's 50V 47mfd cap.
U2 number - OZ9906GN, probably this is the datasheet - https://www.promelec.ru/product/318597/

[R_J]

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

That is NOT C15, C15 is a smd cap that is not populated, those leads are from the electrolytic mounted on the other side marked C429. Where does it connect to that you think it should have voltage on it?

This thread delt with the same power supply https://www.badcaps.net/forum/showth...light=65uh5500

[anupkg1985]

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

It's connected to Emmiter of Q407, shouldn't it have any voltage present on it?

[R_J]

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

Q407 emitter is connected to ground.