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Help: LCD TV not turning on
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Help: LCD TV not turning on

by brad on Sun Aug 09, 2009 1:36 pm

Hi

I'm a noob regarding electronics, but I'm willing to learn. I know I can just throw this TV out and buy another. I'm willing to try and learn how to fix this problem.

My LCD TV is not turning on. Need some help.
This is what I have done so far:

I have an Akai LCT2016 LCD TV
http://g33stone.com/lcdtv/DSCF0091.JPG

The tv has an AC/DC adapter producing 12V 5amps
http://g33stone.com/lcdtv/DSCF0090.JPG

I tested the power going into the TV which produced around 12V
http://g33stone.com/lcdtv/DSCF0098.JPG

I opened up the tv
http://g33stone.com/lcdtv/DSCF0100.JPG

I plugged the power into the board and these are the readings
http://g33stone.com/lcdtv/DSCF0107.JPG
http://g33stone.com/lcdtv/DSCF0111.JPG
http://g33stone.com/lcdtv/DSCF0112.JPG
http://g33stone.com/lcdtv/DSCF0113.JPG

I noticed there are 3 leads coming off the power connector and onto the board
http://g33stone.com/lcdtv/DSCF0114.JPG
http://g33stone.com/lcdtv/DSCF0118.JPG
http://g33stone.com/lcdtv/DSCF0125.JPG
http://g33stone.com/lcdtv/DSCF0130.JPG

Questions:
    - Is the power supply really pushing out 5amps even though the voltage is correct? Does this matter?
    - There are 3 leads coming out of the power connector on the board. What are they for (I'm assuming one is for ground?)? Why does it have only 4.3V and 4.4V? Is there a problem with the connector? Shouldn't I be getting 12V?
    - Are there other areas I should be testing?


Thank you for any advice,

Brad
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Re: Help: LCD TV not turning on

by adafruit on Sun Aug 09, 2009 2:49 pm

does anything light up? is there perhaps a fuse somewhere?

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Re: Help: LCD TV not turning on

by ericzundel on Sun Aug 09, 2009 3:41 pm

First of all, if you are a noob, don't try this with a old CRT style TV or monitor. You'll likely give yourself a nasty shock from one of the large capacitors onboard.

On the jack I use, the third prong on the power jack is there so you can tell when the jack has a plug inserted. I never use it for that - I just solder it to ground. If nothing else, soldering it to the board helps keep it physically mounted.

Here's a an entry at Mouser where you can look at the datasheet:

http://www.mouser.com/Search/ProductDetail.aspx?R=163-7620-Evirtualkey11180000virtualkey163-7620-E

When you read the voltage from an adapter, you have to keep in mind that the voltage is only going to be read correctly when the device is under load. On a wall-wart style supply with just a transformer, you'll get higher voltage readings from your meter until you apply an electrical load. Even then, the voltage will be higher than what's stated on the label, at least until you exceed the maximum listed current. I use a 100 ohm power resistor for that purpose sometimes. On a nice switched power supply, you may get only a tiny voltage reading until you apply load or the reading may look like the voltage is floating (even though the power supply might have a led that lights up!). Again, I use the handy power resistor to test the power supply.

Most modern electronic appliances like TV's are always "on". They have a sleep mode, which is probably what you are likely seeing now which uses very little power (if it is designed correctly). When you press the power switch, it just sends a signal to wake up the processor and start the rest of the circuit.

Your TV shouldn't be pulling 5 amps when it is not on. I couldn't see the settings on your meter, but but you have to measure amperage in series with that kind of meter. They way your probes are set, it looks like you are measuring in parallel and creating an open path from power to ground. Your power supply is controlling the max current and keeping it from going over 5 amps, I'd guess. Usually you assemble some kind of test rig with one of the leads of the power cable cut so you can measure power across the ground going back to the power supply.

If you want to start learning about electronics by diagnosing a circuit, might I suggest a toy, like Billy Bass? I had lots of fun reverse engineering this toy and tapping into the motor circuitry to control it through a microprocessor.

http://ayershome.org/users/eric/robots/billy/Billy.html
Last edited by ericzundel on Sun Aug 09, 2009 6:00 pm, edited 1 time in total.
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Re: Help: LCD TV not turning on

by brad on Sun Aug 09, 2009 4:09 pm

ladyada wrote:does anything light up? is there perhaps a fuse somewhere?



Nothing lights up.

I cannot find any fuses. Should there be a fuse on these LCD TV's??
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Re: Help: LCD TV not turning on

by Amberwolf on Mon Aug 10, 2009 6:07 am

If the TV is really drawing current at the rated level from the power supply, then it is doing something similar to what it is supposed to, to be drawing that power. Most likely it is just not obvious.

Test this: Make sure you have a known good signal into the LCD TV (such as from a DVD playing, preferably something with high contrasst sections like a test pattern with blocks and lines of color/black), but has nothing lighting the display, if you take it out in sunlight or shine a really bright flashlight onto it in such a way that you can see light reflecting inside the screen, does it then have any kind of picture at all?

If so, it means that the main part of the TV is working, but only the baclight is out. That could be a fuse on the backlight inverter board(s), or a problem supplying power to the backlight inverter(s). Even possible to have broken CCFL bulbs, but it's more common to shatter the screen than the bulbs, and that'd be a different looking failure. :)

The fuses on the boards would typically be small SMT fuses, which are sometimes green with the fuse symbol printed on them, but are also sometimes white with a rating printed on them. There are probably other types that look like neither of these, even smaller. Some of the smallest fuses I have seen are as small as the tiny chip resistors and capacitors, perhaps a couple of millimeters long/wide.

One of the most common things I see fail in any electronics is that electrolytic caps blow up or leak, sometimes this is not very visible and only shows a slight swelling, but the cap is no longer doing it's job properly even before this happens. Look up badcaps.net or the wikipedia article about the Capacitor Plague. Both will show you what the problem looks like, so you can visually check for it on your device. Even if you see nothing wrong, caps could still be bad, and generally it's the ones near heatsinks or other heat-radiating parts of a device. Or ones inside unventilated enclosed sections of a device.

Since you don't show close enough images of the boards (just the power connector area) I can't tell if there is a problem or not.
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Re: Help: LCD TV not turning on

by erich81 on Tue Feb 01, 2011 1:23 pm

pictures don't work.

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Re: Help: LCD TV not turning on

by zener on Tue Feb 01, 2011 8:33 pm

Yeah, I am guessing fuse, or fusible resistor or something. But I did not look at any of your pictures or anything yet. Try to trace the voltage until it disappears... Could be a bad solder joint somewhere. How long did it work (if ever)?

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Re: Help: LCD TV not turning on

by Philly on Wed Feb 02, 2011 9:20 am

Resolder all ponts on the power board and every point where the power connections continue. If the 5v supply fails for whatever reason, the tv will not switch on(regardless of 12v presence).
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Re: Help: LCD TV not turning on

by eventhorizon on Wed Feb 02, 2011 9:47 am

I didn't catch if the TV was broken after sometime, or was broken when you first used it.. If you were using that TV for quite a while now, and probably abusing it for something other than just watching TV shows, chances are some of the key components wore out. As to the latter, if it's broken when you first used it, contact your dealer and ask for a warrant..
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Please be positive and constructive with your questions and comments.