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Rick williams
Rick williams, Technician
Category: TV
Satisfied Customers: 7434
Experience:  20 YEARS OF TV REPAIR ALSO HD, DLP LCD AND PLASMA EXPERIENCE
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My LG TV will not turn on. When the power button is pushed

Resolved Question:

My LG TV will not turn on. When the power button is pushed I don't hear the loud click that you usually hear a half second or so after pressing the switch. I have the back of the TV off, and can see that one of LED lights on an AV board lights up when power is turned on, but screen isn't powering up. All fuses are good, and all connectors seem to be plugged in.
Submitted: 4 years ago.
Category: TV
Expert:  Rick williams replied 4 years ago.

Thank you for posting your question on Just Answer! I will be happy to help you with this problem.

 

 

this is a very common sense approach.

 

(Please click on high lighted words)

 

Friend this is a very common problem with LCD and also DLP within the power supply the capacitors

Start to fail and the way you can tell is to check them visually for swelling or expanding of the top.

It will be easy to see the bad caps will not be as flat on the top as the good ones, But also you can have a bad resistor or diode and even a bad regulator. Would like for you to take your meter and place it on DC voltage the positive end on every connector that says a voltage and the negative wire to the panel this is the best ground. Turn on and see if the unit tries to climb, If you don't find one that's trying to climb, another method is to locate a short circuit, place meter on ohms or beep test follow same procedure no voltage should be shorted to ground. And this is the problem,

Customer: replied 4 years ago.

Rick,

 

My TV is a plasma, and its control board much more stuff on it than the one linked to your message. It has hundreds of resistors, what appear to be four separate transformers, three exposed copper coils and a few very large and nasty looking capacitors. I want to be very clear about what I'm doing before I poke around while it has power to it.

 

All the capacitors in the entire set appear to be normal; all are flat at the top.

 

My best guess is that the power failure has something to do with my running the TV with a couple connectors unplugged from the AV boards. I ran it with some cables unplugged several times, but I lost power the first time I ran it with one of the fans unplugged. I understand that this TV has thermatic sensors that will shut down the power if the fans don't turn on. The TV didn't have a chance to warm up before shutting down, but I didn't touch anything to cause a short, or do anything else differently when I lost power, so I don't think the unplugged connectors are a coincidence. Is there a way that I can check if some sort of safety switch has caused the power outage?

 

If you don't think a safety switch of some kind is a likely cause, I don't understand the directions for testing for bad resistors or diodes. You said to set my testor on DC voltage and put "the positive end on every connector that says a voltage." Does that mean I will place the lead on each resistor where it is attached to the power board? You said to ground to the "panel." Is that the metal chasis of the set, or something else? I just want to be really clear before I go poking around.

Expert:  Rick williams replied 4 years ago.

Yes, i do understand, Just wanted you to see the capacitors, This could have been a quick fix, Ok, they are good now we must test.

 

Would like for you to take your meter and place it on DC voltage the positive end on every connector that says a voltage and the negative wire to the panel this is the best ground. Turn on and see if the voltage is present at the VS, VA, V-scan, According to the Panel label, Also remove each board from the power supply to make sure they are not holding down the voltage If you don't find one that's trying to climb, or shows close to what it should be, another method is to locate a short circuit place meter on ohms or beep test follow same procedure no voltage should be shorted to ground. And this is the problem, You can unplug each board one at a time, Starting with the Y-SUS then the Z-SUS.

Customer: replied 4 years ago.

Rick,

 

I don't want to sound dense, but I'm having trouble following the terminology.

 

Please exlain: "every connector that says a voltage." Are you talking about the wire connectors that plug into the board?

 

Does "says a voltage" mean that there are voltages printed on the board near some connectors?

 

I don't understand what the "panel" is where I should ground the tester.

 

I don't understand VS, VA, and V-scan, or where to find the panel label.

 

 

Expert:  Rick williams replied 4 years ago.

Ok, dont want to confuse you,

 

Here are some basic plasma introduction. (click on all high lighted words)

 

 

Normally the parts for this unit is a kit Y-SUSTAINBOARD and Z-SUSTAIN BOARD, this is what most manufacturers would want you to do, purchase them. But go to high lighted words and go through all the voltage checks to find the bad part, here is also a chart that should help a lot, Also this is a picture that will help with identity.

Well Good luck friend, and if my efforts are appreciated, feedback and a bonus will be appreciated

 

Thanks Simplified click here

Customer: replied 4 years ago.

OK, I'm starting to get it. I see that some of the connectors to the boards have voltages printed next to them, and some are labled VS, VA, and Ground. I don't see any labled V-scan yet.

 

I still don't understand where to ground the tester. "Negative wire to the panel" doesn't mean the main negative AC power wire coming from the on/off switch where it connects to the power board does it?

 

Is a "panel" the same thing as a "board?"

Expert:  Rick williams replied 4 years ago.

The panel is the LCD, all of that metal is a ground friend. Any metal is ground,

 

Now put the positive on each voltage and see if it reads before shutting down

Customer: replied 4 years ago.

I get no voltage reading on the connectors the go from the power board to the Contol board. I get no voltage from the connectors marked with a voltage to the Y sus board, but I do get .5V readings from a connector to the Y sus board that's labled Vs.

 

There are three connectors to the AV boards. I got no readings from the middle one, and only a .65V reading from a couple pins on the third that were marked 3.5V. However, when I unplug the smallest one, many additional LED lights come on on the AV boards, I hear clicking and humming, and the voltage goes up to the correct level on the connector that was previously reading .65V. The pins on the small connector also read close to the correct voltage.

 

I get no voltage from the heavy-gauge wires leading to the z sus, except for a brief .1 from one pin marked Vs

Expert:  Rick williams replied 4 years ago.
If you have no VS VA with Yand Z disconnected you have a bad power supply
Customer: replied 4 years ago.

Rick, I haven't been able to open the files you gave me the links to, so I'm still a bit slow. I just disconnected the connectors from the power board to the Y and Z boards, and I get no voltage readings on the connector on the power board that has pins marked Va and Vs. There's only one connector with pins marked like that.

 

Can the power supply be fixed?

Customer: replied 4 years ago.
Is there any significance to the AV boards lighting up, and the voltage on a different connector to the AV boards going up, when that one connector from the pwr board to the AV board is disconnected?
Expert:  Rick williams replied 4 years ago.
Do you get your VS VA when this board is disconnected?
Customer: replied 4 years ago.
I get a reading of "1" on the three Vs pins and the two Va pins when I have that connector from the power board to one of the AV boards unplugged. I also hear clicking when I turn the power on that sounds very similar to the usual click you hear when everything is working normally.
Customer: replied 4 years ago.

The connector that seems to make such a big difference when it's disconnected has 7 pins. They're labled:

 

AC- ON

RL- ON

STBY- 5V

GND

VS- ON

5VMONI

POD

 

I get right around 5V from all of them, except of course GRD. Some are around 4.85V, and a couple are just over 5V

Expert:  Rick williams replied 4 years ago.

No 190vdc when nothing is connected to it (bad power supply) do have 190vdc when just unpluging main board

 

(bad main board)

Customer: replied 4 years ago.

Rick,

 

Sorry, but I don't understand.

Expert:  Rick williams replied 4 years ago.

The connector that you are removing, You just sent information on, this is the main board, what is it you don't understand,

 

You mention 5vdc see if any change when you unplug it from the power supply.

 

 

Would like for you to take your meter and place it on DC voltage the positive end on every connector that says a voltage and the negative wire to the panel this is the best ground. Turn on and see if the voltage is present at the VS, VA, V-scan, According to the Panel label, Also remove each board from the power supply to make sure they are not holding down the voltage If you don't find one that's trying to climb, or shows close to what it should be, another method is to locate a short circuit place meter on ohms or beep test follow same procedure no voltage should be shorted to ground. And this is the problem, You can unplug each board one at a time, Starting with the Y-SUS then the Z-SUS.

 



Edited by Rick williams on 2/1/2010 at 2:28 AM EST
Customer: replied 4 years ago.

I don't understand what your previous message means at all.

 

The connector that I'm removing is on the power supply board, and it connects to what I'm calling the AV boards (there are two boards connected together by three ribbon cables that have all the audio and vidio input/output jacks on them). When I press the power switch with this particular connector plugged in, nothing happens except a single LED light comes on on one of the AV boards. When I disconnect that connector I hear the normal loud click coming from the power supply board, and LED lights come on all over both AV boards, but I still don't get a picture. I also don't see the power light on the front of the TV.

 

 

Expert:  Rick williams replied 4 years ago.

Ok, Now this board is bad the AV board as you call it, I call it the main board.

 

When it is disconnected and you here your normal clicks what is the voltage at vs va ??

 

are they present??

Customer: replied 4 years ago.
OK, when that connector to the main board is uplugged and I hear the click, the Va and Vs pins on a different connector on the power board read 1 . I get a one and several empty spaces, then a decimal point. There is one pin on the unplugged connector to the main board labled Vs- On. I get a reading of 4.85 Vdc on that pin. There are two other connectors from the power board to the main board. When that one connector is unplugged, I get about 5Vdc on pins from one of the other connectors that I don't get when it's plugged in.
Expert:  Rick williams replied 4 years ago.

All i need to know is when you press the power button do you have voltage at the VS VA connector on the power supply, if not unplug the Y and Z board from the power supply, not the main board turn on again see if you have the voltage then,, Also when you press the power on see if the VS- goes low then back up to 5vdc on the main board.

Customer: replied 4 years ago.

Rick,

 

There's no voltage at the Vs Va connector on the Power Board when all other connectors are plugged in and power button is on.

 

There's no voltage at that connector when Y is unplugged, when Z is unplugged, or when both are unplugged.

 

I'm not clear about the last part of your previous message where you said, "when you press the power on see if the VS- goes low then back up to 5vdc on the main board." You said you refer to the boards with all of the A/V input jacks as the Main Board. I don't see anything labled Vs on those boards.

 

The Power Board is where I have a connector and pins marked Va and Vs. That connector is the one with wires to the Y sus board. I only get any reading at that connector when I unplug the one of the connectors from the power board to the Main Board (A/V board). I told you earlier I was getting a 1 followed by spaces and a decimal. I wasn't expecting a high voltage, and I had my tester on a low scale. Set on a higher scale, when I unplug that particular connector from Power Board to the Main Board (A/V board), I get 60Vdc at the Va pin, and around 195Vdc at the Vs pins. I don't see drops in voltage on the Vs pins...when powered on, it just rises to around 195V and stays there.

 

 

Expert:  Rick williams replied 4 years ago.
Yes, Your problem is the main board, its holding down the voltage, Or the power on command on the main board isn't working
Customer: replied 4 years ago.

Is there a way for me to narrow it down to a component on the board?

 

Could the power on command board have a problem as a result of me powering up the TV with one of the fans disconnected from the Main (A/V) board? That's only thing I did different when I lost power.

Expert:  Rick williams replied 4 years ago.
You should purchase a schematic but this is time consuming and may be costly if you dont have a scope, And troubleshooting skills, Some cases cheaper to purchase the board because some Chips are more expensive than the unit itself
Customer: replied 4 years ago.

On my TV the Main Board is two big boards connected by three ribbon cables, so I may have two boards to replace, unless I can narrow it down.

 

I never gave the full background about why I was working on the TV to begin with. I developed a verticle red stripe on the screen, which I found in many posts online is really common with my LG model. The problem is the "Control Board" (or PCB assembly), which is underneath the the Main Boards. I was trying to repair the solder joints in the the Control board (while waiting for my new board to arrive), and was checking to see if my resoldering worked by turning the TV on with the Main Board moved out of the way so I could get at the Control Board. I did that several different times, but unplugged a couple additional connectors to the Main Board for the first time when I lost power. I just wonder if it's reasonable that a component/s on the Main Board would be destroyed by powering up with some connectors unplugged? Like I said, the only difference was a fan, a speaker, and a connecor to all the buttons on the front of the set. I think the fan is the only relevant possibility. If there's a thermatic safety switch, that would be my first guess...if I could find it.

Expert:  Rick williams replied 4 years ago.

please can you send me a picture of this unit.

 

Does your main board look like this and if so what are you looking at with two boards.



Edited by Rick williams on 2/3/2010 at 5:23 AM EST
Expert:  Rick williams replied 4 years ago.
.
Customer: replied 4 years ago.

That part is one of two boards that're connected by three ribbon cables. Both boards are mounted in a metal tray. Here's a photo I cut from the repair blog on another site. The bottom of the power board is at the top of the picture.

 

input-board

Customer: replied 4 years ago.

Here's a photo of the whole back of my set.

 

graphic

Expert:  Rick williams replied 4 years ago.

OK i see, friend, well do you remember telling me when you unplug the AV board you have VS of around 190vdc?

this is the voltage you should have, And it also has your power on command, there is no way for you to isolate with these boards, As you can see they are all digital and would require a scope to see sign waves, Your problem is the AV board as you call it

Customer: replied 4 years ago.

Would you recommend taking the set to a repair shop, or just replacing the main boards? I see both on the parts link that you sent earlier, and each is $59, used.

 

What is the power on command? Is that a component, or a command signal that tells the power board to turn the set on?

Expert:  Rick williams replied 4 years ago.

Thats good because this amount is still smaller than a labor charge, I would replace the boards, starting with the AV the one that has the power on command.

And yes the main board tells the power supply to turn on, it is a signal that goes to the Power supply, This should be clear to you unless i am missing something, You said when you disconnect this board you have 190vdc, this should have told you that this board is bad because it holds down the 190vdc

If i'm clear on your diagnosis.

Rick williams, Technician
Category: TV
Satisfied Customers: 7434
Experience: 20 YEARS OF TV REPAIR ALSO HD, DLP LCD AND PLASMA EXPERIENCE
Rick williams and 4 other TV Specialists are ready to help you
Customer: replied 4 years ago.

Hello Rick,

 

I ordered one of the two boards that make up the main board on my set and I just finished installing it. Sure enough, it works. Thanks for your help in troubleshooting the problem. I'm still wondering how I could have possibly damaged that board while trying to repair control board, but I guess something as simple as static could have harmed it. My only problem now is that the remote quite working somewhere along the way too, also for no readily apparent reason. Thanks again,

 

John

Customer: replied 4 years ago.

Rick,

 

I meant to increase the amount that paid for your help, but it didn't work out properly. I'd added a few bucks to the deposit and assumed that would go to you when I accepted the answer. Then during check out I had an opportunity to add a tip, so I added a couple more bucks, but it looks like that tip amount was the only amount paid. I don't see a way to add to your payment without accepting another answer and paying the original amount again, which is more than I was planning on.

Expert:  Rick williams replied 4 years ago.
Its ok friend, Good luck to you

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