LG PSU EAY40504401 (LGP32-08H) repair

[frica]

Re: LG PSU EAY40504401 (LGP32-08H) repair

Dear R_J

Thank you for your clear response! I will take note: the best test is measure the zener voltage in circuit and with the PBC power on.

Thank you R_J!! I read many message from your. I am like a fan of you!!

[yohnsee]

Re: LG PSU EAY40504401 (LGP32-08H) repair

Hello yohnsee:

Wondeful that you could repair the PSU!!

For the very newbie one in electronic repair, could you explain in detail how do you test the zener diode especially the regulator function?

I know that a zener is like a normal dode in forward polarization and as a regulator in inverse polarization. With a multimeter and the PBC no energized I know test the diode function. But how did you test the regulator function using a multimeter in ohm scale? or only tested if both ends of zener had very low ohmios?

do you test in ohmio scale o in diode scale? Do you test in circuit? did you test in forward polarization (positive probe in Anode and negative probe in catode) or/and inverse polizarization?

thank you!!

Hello and welcome to the forum!

First of all, as I see you have a lot to learn about electronics, but don't worry, no one was born with this knowledge. And second, you came to the right place, on badcaps every member is willing to help (so far I have noticed).
R_J told you how you can test the zener breakdown, but if you are more a visual type, watch this: Zener testing.
First when I test a bad behaving circuit, I try to break down it to parts, and focus only on the part that seems problematic. In my case, the 5V standby voltage was fine, only the switched voltages showed problems. So I didn't bother with the standby circuit, instead I focused on the rest of the schematic. You could read about switchmode power supplies on many places, and when you understand the main working concept of it, then you can guess which part works abnormal. Reading back my first post, now it seems obvious that the feedback of the regulator was faulty. And indeed, this zener let the voltage rise above normal levels (didn't clamp as it should have) and that's why I had overvoltage on the secondary side. It may be a bad advice, but I always imagined the zener diode as:
a regular diode, unless it gets higher voltage on the cathode side than the rated breakdown voltage, because in this case it will conduct like a wire. But as soon as this happens, the voltage drops below breakdown level and the diode function comes back. All of the above happens in a fraction of a second, so you or your multimeter won't notice it. The only thing you or the circuit will see is steady voltage. Of course, it can be applied to signaling, you can't draw power from it.
Hope this helps.

[frica]

Re: LG PSU EAY40504401 (LGP32-08H) repair

Thanks for your words yohnsee!! Yes I see that this is the best electronic forum I found (well I visit other forum in spanish that is good also). Since several years ago I have learned much about electronic repair and love discover what is the culprit! I have many notes and documents save in my PC. thanks for the video! And thanks for the notes about zeners!

[gorgi991]

Re: LG PSU EAY40504401 (LGP32-08H) repair

hello i have the same pcb
in the 24v rail i get 13volt, light goes blue but the inverter lights doesnt light up,can you suggest me where to look at?

[peterkos2]

Re: LG PSU EAY40504401 (LGP32-08H) repair

Hello everyone.
I also have a problem with this power supply.
After connecting to the mains, the st-by LED flashes - weaker-stronger, turns off, weaker, stronger, turns off.
It tries to turn on. I checked the capacitors - one was weaker, I changed it but still the same and in a minute, two it turns on and works.
I resoldered some connections, but now I don't know what to do next.
I also checked the diodes and mosfets - they look OK.
Sometimes it can be turned on for the first time
Thank you for your response

[yohnsee]

Re: LG PSU EAY40504401 (LGP32-08H) repair

Hello everyone.
I also have a problem with this power supply.
After connecting to the mains, the st-by LED flashes - weaker-stronger, turns off, weaker, stronger, turns off.
It tries to turn on. I checked the capacitors - one was weaker, I changed it but still the same and in a minute, two it turns on and works.
I resoldered some connections, but now I don't know what to do next.
I also checked the diodes and mosfets - they look OK.
Sometimes it can be turned on for the first time
Thank you for your response

Hello,
So if I get it right, you did not remove the PSU from the TV, and all the symptoms you have can be seen when you want to start the TV?
From what you described, I can only think of a capacitor problem.
Think about it: standby led flashing stronger-weaker-stronger-(then the TV should turn on). But in your case it only starts the blink sequence again. From this I would assume the PSU does not have the needed power reserves to start the display, MB and backlight at the same time. Either one of these components ask for higher current than it should, or the PSU does not have what is needed.
You also wrote, you checked the capacitors. Did you measure them, or just took a look at them? If it was with some measuring tool, what was it?
(many people would not share my views, but I have a rule for myself: if the PSU I am about to repair is older than 5 years, I blindly re-cap the whole board before checking anything else. This way I can be sure, the caps are not playing funny games with me)
I wouldn't suspect the semiconductors first, as you tested (or optically checked) the diodes and FETs.
Also, for fun, you can do the following test: Remove the PSU, put it in the refrigerator for 15 minutes (or freeze it a little bit with freeze spray, if you have such thing), then reconnect it to the TV, and try to start. I bet it won't turn on.
Then, grab a hairdryer, and get the PSU board up to like 40-50 degress celsius. It can even stay in the TV for the time. After it is good and warm, it will start instantly.
The tests above also conclude that the PSU has capacitors that has almost lost all of their capacity. If you warm it up a little bit, their capacitance increases temporary. That happens, when you try to start the TV at room temperature, and it struggles for 1-2 minutes, then starts. During this time the capacitors get a bit warmer, thus having that little plus juice to start the circuits.
Let me know, if it helped.

[peterkos2]

Re: LG PSU EAY40504401 (LGP32-08H) repair

I tested the capacitors with an ESR meter, they all looked fine. I measured the mosfets and diodes with a diode test - fine.

[peterkos2]

Re: LG PSU EAY40504401 (LGP32-08H) repair

You were right, I put it in the fridge for 15 minutes and after connecting it just tried to turn on. I heated it with a heat gun and after a while it turned on. It is interesting that I measured the capacitors. It will probably be necessary to desolder and then measure. Thank you so far

[yohnsee]

Re: LG PSU EAY40504401 (LGP32-08H) repair

You were right, I put it in the fridge for 15 minutes and after connecting it just tried to turn on. I heated it with a heat gun and after a while it turned on. It is interesting that I measured the capacitors. It will probably be necessary to desolder and then measure. Thank you so far

In-circuit measurements can lead you in the wrong direction. Nevertheless, I am curious about the solution.