Lg 60pz250n-zb

[Joepeff]

I'll start off with saying that I'm very new to tv-repairs.
With that said, I have an LG 60PZ250N-ZB in my home, which I happened to find in the garbage room.

The TV worked just fine, but I noticed some grainy noise, going mainly horizontally across the screen, in certain lighting. Could be bright or dark, mostly bright.

After some searching I figured it could be what's known as "mal discharge" so I got myself some documentation from LG for this.

Then I found this site, and Topcat wrote about the "sparklies".

I decided to test the Va and Vs with a DMM and found the voltages off by a volt or so. Keep in mind that I have a very cheap DMM. I am thinking this isn't the brightest thing to use, but I have an incredibly limited budget.

So, I adjusted the pots to get the correct Va and Vs, but upon testing Vs on the YSUS board I happened to short the 5v and the Vs (55v) lines.
I hear buzzing from the YSUS board when I plug in the AC cord, which I heard prior to shorting, and the buzzing now stops ~3 seconds after plugging in.

On the control board, the green LED flashes 4 times (long, long, short, short). I have no idea how the LED was lighting before shorting because I did not look.

So, without jumping to any further conclusions, I'd like to ask for some opinions on what to do next. Should I replace the PSU? I'm not quite sure how to test what components might have fried since I have very limited equipment.

Thanks for taking the time to read my post.

[Joepeff]

Re: Lg 60pz250n-zb

After plugging in the AC cord again to do some testing, i found that Va and Vs was lower than I'd left it. After adjusting to the correct value I heard a click from the PSU and the voltage was steadily dropping.

I could sure use some help here

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So, as it turns out, I can't set Va/Vs to the correct values. Va=55 and Vs=201.
Vs is currently at 210 and wont go under 208 as I lower the pot. It just ends up shutting off the TV, which is the click I heard.

[Joepeff]

Re: Lg 60pz250n-zb

I suspect the power supply might be done for.
I disconnected all the boards, and the voltage on Vs keeps going up even though the pot is set to minimum...

[Joepeff]

Re: Lg 60pz250n-zb

Any pointers would be appreciated, even if it's pointing me in the direction of giving up.

[Andrew F. Ali]

Re: Lg 60pz250n-zb

Could we at least get photos to see what we are dealing with? I suspect this is why you aren't getting responses. I would need to see a clear focused close up of the PSU and all its connectors so I can read the pin labels. Thanks.

[tvtimmy]

Re: Lg 60pz250n-zb

Post a picture of the Asus board. Top and bottom. Make sure your model number is correct.
DO NOT RUN THE SET WITH ANY MOUNTING SCREWS REMOVED !!!!

[Joepeff]

Re: Lg 60pz250n-zb

Here are some photos of the PSU and connectors along with an overview shot of all the boards.

I'm not sure which is the Asus board. I only see the Ysus and Zsus boards.

Thanks for the response!

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Edit: Sorry about the flipped images. They're cropped and fixed now.

[Andrew F. Ali]

Re: Lg 60pz250n-zb

Disconnect the connector on the PSU to the Main Bd. Connect GND and Auto-GND with a jumper. Connect a 100Ohm resistor across 5.1 and RL-ON. connect another 100Ohm resistor across 5.1 and M-ON. Make a test lamp by connecting two 120Vac household lightbulbs in series. Disconnect P811 to the Y-sus Bd. Connect the test lamp across Vs and GND on P811. Apply the 120Vac. If the PSU is good the test lamp should come ON and light-up bright. Measure Vs, Va and M5V on P811. (You may have to readjust the pot to get VS on the correct voltage as stated on the label , as you did interfere with it. If all these test show good then PSU is good if not then the PSU is at fault.

[Joepeff]

Re: Lg 60pz250n-zb

Apply the 120Vac. If the PSU is good the test lamp should come ON and light-up bright. Measure Vs, Va and M5V on P811. (You may have to readjust the pot to get VS on the correct voltage as stated on the label , as you did interfere with it. If all these test show good then PSU is good if not then the PSU is at fault.

As I've mentioned, the pots no longer help lower the voltages. The Vs and Va pots are on minimum. Vs rises until a peak of 256V

Besides that, I'm curious as to why I should use 120Vac lightbulbs and apply 120Vac to the PSU, since we use 230Vac in Sweden..
If I should use our mains line voltage (230Vac) instead, should I still do two 230Vac lightbulbs in series?

[Andrew F. Ali]

Re: Lg 60pz250n-zb

OK. I didn't read your profile and country of origin. So use one 230Vac light bulb as your test lamp across Vs and GND then plug the power cable into the 230Vac. Some PSU will go into protect mode without a load and shutdown. Hence the 230Vac household lightbulb as a load for Vs.

This is part of what you said in Post 1: "So, I adjusted the pots to get the correct Va and Vs, but upon testing Vs on the YSUS board I happened to short the 5v and the Vs (55v) lines.
I hear buzzing from the YSUS board when I plug in the AC cord, which I heard prior to shorting, and the buzzing now stops ~3 seconds after plugging in."
So I was just trying to help you out by showing how to self-test your PSU to verify it is OK so we could look elsewhere to fix this TV.
BTW the Va would be around 55V and the Vs maybe round185-210V. I am guessing here as I did not see a photo of the label voltages on the Panel.

[Joepeff]

Re: Lg 60pz250n-zb

I see.
Well when running only the PSU (no other boards connected) the PSU will not go into protect mode. Perhaps the voltage climbs due to no load. I don't know.

To be clear: Vs and Va were both off by about 1V prior to testing, so I fixed that. I then shorted M5V and Va while testing the voltages on the power input of the Ysus bd.

1) Should I leave Zsus bd plugged in?
2) Should I leave ctrl bd plugged in?

I need to get my hands on some resistors before I can do this.


Here is an image of the panel voltage label and one of where the short occured on the Ysus bd.

[Andrew F. Ali]

Re: Lg 60pz250n-zb

Disconnect the Z-sus Bd as well, when performing the test I suggested. Without a load on the Vs it may go into protect mode. Must test PSU with the light bulb load. Shorting the 5V on the Y-sus Bd would affect the PSU and not necessarily the Y-sus Bd. So you are looking for Vs at 201Vdc and Va at 55Vdc. Measuring/testing without the load will give erroneous result.

[R_J]

Re: Lg 60pz250n-zb

If you shorted Va55 volts to M5volts you damaged the power supply M5 volt circuit. What voltage do you have on M5 now? is it 0?
Check the voltage on J54 of the power supply, It should be 5 to 6 volts
If it is zero volts, check Q353 and the zener diode next to it.
Chck F302 fuse on the power supply

[Joepeff]

Re: Lg 60pz250n-zb

Since I don't have any resistors at the moment I can't run Andrews tests.
Having all boards disconnected, including Ctrl Bd, I tested M5V on J54.
With no load it read 7.3V.

I can't find Q353, and I can't find a schematic for my board in order to locate it. Could you highlight on the board where I might find it?
I searched for zener diodes to help me locate Q353 to no avail.
Only ZD101 and Q101 were next to each other, and ZD101 is the only zener diode I can find.

F302 is fine.

[tvtimmy]

Re: Lg 60pz250n-zb

Check all 4 fuses on the ysus. Then check all on the ysus. Remove both boards from the tv and look at the solder that is on the bottom side on the 3 copper coils. A crack or a ring is bad.

[R_J]

Re: Lg 60pz250n-zb

Do you have the M5 voltage at the plug where you shorted the M5v to Va?
Are you sure you shorted Va to M5 or was it Va shorted to ground (the other pin next to Va)
If there is no regulation on the Vs or Va, check the components around the adjustment controls, likely either an open resistor like R515 (white ceramic) or the control. or a shorted transistor or diode.


I don't have a schematic only the picture of the board.

[Joepeff]

Re: Lg 60pz250n-zb

Check all 4 fuses on the ysus. Then check all on the ysus. Remove both boards from the tv and look at the solder that is on the bottom side on the 3 copper coils. A crack or a ring is bad.

Indeed each of the three rings have a ring on one joint.
Bad in what sense?
I'm going to re-solder those joints now.

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Edit: turns out my soldering iron wont go hot enough for that.

[Joepeff]

Re: Lg 60pz250n-zb

Do you have the M5 voltage at the plug where you shorted the M5v to Va?
Are you sure you shorted Va to M5 or was it Va shorted to ground (the other pin next to Va)

Yes, I am sure. I shorted the M5 with Va using my positive test lead of my DMM.
I'm quite sure the negative lead was grounded as I was testing voltages.

[tvtimmy]

Re: Lg 60pz250n-zb

The bad solder joints are causing your malcharge issue. Resoldering with dead solder will fix this problem. Check the fuses and tighten the screws.

[Joepeff]

Re: Lg 60pz250n-zb

I'm going to invest in a soldering station and some resistors, and I will post here again once I've performed the tests suggested.

Also, as the solder is wouldn't melt with my 30W soldering iron, I'm curious what solder I should repair my board with. Any tips?
Also, what is dead solder?