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Michael Hannigan
Michael Hannigan, Technician
Category: TV
Satisfied Customers: 11167
Experience:  25+ Years Experience in Computers and Electronics
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My name is ***** *****. I pasted a detailed description of

Customer Question

Customer: My name is ***** *****. I pasted a detailed description of how my LG 42LC7D has no video. Should I paste it again?
JA: Thanks. Can you give me any more details about your issue?
Customer: LG 42LC7D audio but no video…I was given this TV so don’t know much of its history. When turning the power on the front LED flashes green eight times, then goes solid green. There is a click and “power up” noise during this time. Fiddling with the control buttons brings up white noise from the speakers. The power supply capacitors all look good (no bulging or heat defects). With power on, the voltage measurements from P201 seem to be OK except for maybe these two: Pin 11: 0V with P201 unplugged, 6.1V plugged Pin 13: also 0V with P201 unplugged, 1.95 pluggedVoltages at P202 all seem very close to values on the circuit board. (I can list all voltages if this might help.)Is there any further testing I can do to better determine which board(s) to replace in order to get the video to work again? Or could the problem be with some other component?Thanks,***** *****
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Submitted: 11 months ago.
Category: TV
Expert:  Michael Hannigan replied 11 months ago.

Hello. My name is Michael. I can help you with your question.

The most common problem on this model, by far, are the capacitors on the power supply. But since you have already checked that and ruled it out, the first thing I am going to do here is upload the service manual to my OneDrive so you can download a copy. Here is the link:

https://onedrive.live.com/redir?resid=6531C5E083B5BD4D!9781&authkey=!AA7xi0iYaxbLSlI&ithint=file%2cpdf

Mike

Customer: replied 11 months ago.
Thanks Mike, but I've already looked through that and found it pretty dense. So you think it might be the main board? Those voltage values don't surprise?
Expert:  Michael Hannigan replied 11 months ago.

There are two separate control inputs on P201. There is the On/Off input which you have overridden, but the last pin on the other end of P201 is '3.4V ON', so the 0V doesn't surprise me. I think you have a bad main board, yes.

Customer: replied 11 months ago.
Thanks Mike, some assurance that the problem was probably in the main board is what I was looking for. I'll order a replacement today. Is there any problem with keeping this thread open until it comes in and can be installed? I'd like to be able to finish this story with you, and possible future readers.
Customer: replied 11 months ago.
Oh... One further question: the exact replacement main board is often listed as being for the UK or Australia LG models. Yet US sellers are offering parts presumably from sets dismantled in the US. I won't be facing any signal processing issues with a UK/Australia board, right?
FWIW, here is the board number: EAX38589402(11)
Here is the number off the coax module attached to the board: EBL39544401
Customer: replied 11 months ago.
Sorry, that add-on question is probably beyond the scope of what can be expected here. My research so far seems to indicate that the UK/Australia boards are extensively used in the US.
Expert:  Michael Hannigan replied 11 months ago.

Sorry. the system didn't alert me to your reply it seems.

It is true that UK/AZ/US boards are often the same. You should try to get an exact match for the number on the board. Occaisionally, one revision of the board is not compatible with other revisions of the board because other electronics sometimes change when they make a revision. But if you can't find the original board, usually the site will be smart enough to tell you whether it has to be the exact number or not. Or if it is compatible with more than one.

Customer: replied 11 months ago.
Great! Thanks for that board info. I've ordered a main board with both numbers matching. It's due on or before 12/24/15. I'll follow up here with the results.
Appreciatively,
Patrick
Expert:  Michael Hannigan replied 11 months ago.

OK, if the numbers match, then you are all set. That will be a fun Christmas Eve!

If you wouldn't mind - if you rate my service - it will stop the question from closing or going back into the open question pool - so that when you reply, I will be notified.

Mike

Customer: replied 11 months ago.
Well, that didn't work. The board numbers match, and there was no problem with installing it, but the only difference is that the green LED on the front panel flashes five times (instead of eight) before going solid. I'm also not sure that the audio is working any more. So either the replacement board (purchased through www.ElectroPartsOnline.com) is bad, or this TV has some other problem. Any suggestions?
Expert:  Michael Hannigan replied 11 months ago.

Since the symptoms changed, I would say that the board is defective. I would ask them to send you a board that they have tested and they are certain works. Audio is processed by the main board, so if that is having a problem now as well, then it would make sense that the main board is the problem.

Customer: replied 11 months ago.
Thanks for getting back to me so quickly - on Christmas eve no less. I didn't consider that you might be contractually required to respond within a certain number of hours. Sorry if I interrupted your holiday!
So I just got off the phone with ElectroParts. They said they'd ship out a new board. It may even go out today. 'Will post again with the results with the new board.
Expert:  Michael Hannigan replied 11 months ago.

Thanks... you didn't interrupt anything! I was stuffed by the time I responded.

Let me know how you make out.

Mike

Customer: replied 11 months ago.
Well, some progress has been made with the second replacement board. In the mean time I learned to shine a flashlight into the screen to check whether an image is being produced. It turns out the the original board, and the first board, WERE producing some images. They both produced no-signal static ("snow"). But the tv would not respond properly to keyboard/remote controls so tuning an antenna signal, and sound levels, only sometimes/partially worked. Plus the image produced by the first replacement board we distorted in wavy lines. (Yes, I took extra care to make sure all main board connections were properly seated.)The second replacement seems to be producing an image, can tune into an antenna signal and the tv responds to controls. It's just that there's no backlight.So my current theory...
- Original and first replacement main boards were bad
- Second replacement main board is good.
- Both inverter boards are bad
How does this sound?
Expert:  Michael Hannigan replied 11 months ago.

That all sounds correct. Yes. It looks like you are extremely close. If everything works now except for the backlight, then it's just the inverter boards.

It's not uncommon to have to go through more than one replacement board when they are "refurbished" (used). Unfortunately, many of them are not tested before they are sent out. And often, when one board goes, more than one goes, so not all boards pulled from a set that are assumed to be working actually are.

Customer: replied 11 months ago.
Thanks for that info. I've purchased replacement inverter boards through ebay, they're scheduled to arrive on or about 1/11. This purchase is for a complete set of boards for a 42LC7D, so I'll have trouble-shooting options if some other problem comes up.'Will let you know what happens.
Customer: replied 11 months ago.
The boards came in early and there's some progress to report... The replacement inverter boards now cause the backlight to show some signs of life. When turning on the tv, the red power light will flash green a number of times, then the backlight will flash. Sometimes the flash is very brief, other times it flickers for a second. One about the fourth attempt to turn the tv on, the backlight stayed on but there was a somewhat dark horizontal band across the screen. The video image seemed clear, it the backlight seemed to have a horizontal smudge. Over the 15 minutes of this test run, the dark band may have brightened a little, but it never went away. The other thing was that the inverter boards were making a pretty loud buzzing noise that varied depending upon the brightness of the video image. Maybe this is normal and just seemed louder since the back cover was off the tv. This buzzing definitely diminished as the tv warmed up. The backlight remained on for the 15 minutes or so of the test run - until I turned off the tv. But the backlight never would turn on again after many later attempts.I've tried swapping out the main and power supply boards with the replacements from this complete set. But the problem remains. Going back to the original master inverter brought the tv back to the original problem of no backlight response at all. So the old inverter boards seem to have a problem.So now what? Could it be that the cf light units themselves are bad? On LCD laptops these seem to be replaceable, but so far I'm finding no encouragement that LCD tv cf units can be replaced. Am I missing some clue in my debugging? Or is there some other kind of test I could try? How about the trick to use the bulb from a household cf lamp, connected to the inverter output? Would this be a reliable test of the invert boards?Help!
Expert:  Michael Hannigan replied 11 months ago.

Are the new inverter boards new or used?

So... it is possible that there is something else causing these boards to go bad. The buzzing in the inverter to some extent is normal, but loud buzzing may mean that they were the wrong boards or getting the wrong voltage.

Mike

Customer: replied 11 months ago.
They are used, supposedly from a working tv. They are getting 24 volts from all pins.
Expert:  Michael Hannigan replied 11 months ago.

OK. Should be working. But as I said about used parts, you never know.