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

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.

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.

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?"

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

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?

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

Rick,

Sorry, but I don't understand.

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.

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.

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.

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.

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.

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

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?

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

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.