Anyone know anything about repairing flat screen TV's?

Hey all, i know there a lot of electrical engineers and others who just know a lot about electronics on here so hopefully someone can help me! I have an Emerson 50" LED TV and it stopped working recently. Can anyone help me try and troubleshoot what might be wrong? I'm thinking it's either the power supply board or the main board. I've inspected both boards and there is no obvious sign of anything bad like burn marks, a swollen capacitor, etc.. Also, I checked the fuse for the 120Vac in and it's got continuity. I'd like to determine if the power supply board is functioning by looking for Vdc to the main board. Does this sound like the correct approach? If so anyone know how to determine which pins of the ribbon cable would be carrying the V? Thanks.

It sounds like you're taking the correct approach. If there's no picture or sound, it's probably related to the power supply. Generally the power traces are heavier than signal traces, and you can usually spot which one is the ground trace by following it to the large area of copper on the underside of the printed circuit board, either visually or with an ohmmeter.

You usually end up having to buy the service manual to determine the pin outs from the power supply. The service manual will also provide schematics and component values that may exist only a codes on the components themselves. The manual often also provides trouble shooting tips and procedures to identify exactly what part has failed, although that is generally at the field replaceable unit level rather than the component level.

I would point out that there may be things other than just the power supply on the board. It generally makes sense to put as many of the high power parts on the power supply board as you can. The other issue is you usually need the pin out because there are often several different voltages provided by the power supply, and it is a question of figuring out that not only is it a power supply, but which of the multiple voltages has failed. Sometimes even if you can figure it out, the supply board has such a high level of integration that it may not be practical to fix it at the component level.

I trust you have verified that the on/off switch doesn't work either (I have seen people actually take apart TV's when it turned out the only thing wrong was the battery in the remote control was dead!).

LOL

WAAAAY back part of my job (part time when in school) was fixing the room TV's for a Holiday Inn, and, well, you'd be amazed at the lack of diagnostic prowess that's out there. Plugging them in, replacing the batteries or hitting the reset buttons would fix ~ 80% of the complaints.

That would be AFTER the hotel staff tried to take care of it before asking me to check it out.

I started doing that when I was 12.



LED TV's did not exist yet, in my world at least. (~ 1969-ish?)

Use google or youtube. You may something related.

Thanks for the help guys. I've tried google and youtube and continue to throw out searches whenever I think about it and have a moment. It's been tough to find this deep of technical information through those resources. Also, the first things i did were check the remote, plug in to a different outlet, even try some "reset" procedures i read about that involved pressing some kind of button combination for some amount of time that might magically reset it. To no avail nonetheless. That's a good point about the power traces being heavier than the signal traces, I'll look for that. Also a good point about the power supply supplying multiple voltages. I think i'm going to look into getting ahold of a service manual that sounds like it provide a lot of the information i'm looking for. Thanks again everyone.

Dave Jones on the EEVblog, http://www.eevblog.com/ , recently did a couple of videos where he did some troubleshooting on a bad plasma TV. It might be of interest and provide hints of the sorts of things you should be looking for.

For a TV that is completely dead... bad connections or blown fuses seem like the obvious thing to look for. If there are boards that are clearly power supply boards, then a check of input and output power could/should help narrow down the problem.

A service manual or schematic would help... just knowing what voltages are expected at different points is a big advantage in narrowing down the problem area. Knowing how to fix a bad section of circuitry is a separate issue, but we can cross that bridge when we get to it.

Assuming it's a switching power supply, take a handheld AM radio, tune it to an empty spot on the dial, preferably at the low end of the dial, and hold it near the power supply while it's plugged in. If you don't hear anything other than AC hum, the switching oscillator(s) isn't working. If you hear a loud whine, then the oscillator is working and you can rule out a portion of the input side of the power supply and focus on the output side.

You can troubleshoot more things with an audio amplifier that you think.