Help: LCD TV not turning on

[bradsmith]

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

 

[creakndale]

I believe that the TV is pulling too much current probably due to a fault in it's CCFL (Cold Cathode Fluorescent Tube) inverter.

The power supply has built-in circuitry that protects itself by lowering it's output voltage when it tries to provide excessive current. This keeps it from overheating when a power fault occurs.

It is unlikely that the DC Power Jack is the problem. Generally, the 3 contacts on a DC power jack signify:
1) Power
2) Ground
3) NC (Normally Closed) switch contact
You can look at this datasheet to see how the 3 leads work.
http://www.cui.com/pdffiles/PJ-102B.pdf

First, I would do a careful inspection of all components on both circuit boards looking for any burnt areas or capacitors with leaking or bulging tops. Make sure the circuit boards are not inadvertently touching the metal backplate.

Second, I would disconnect the inverter board's connector (the inverter drives the CCFL backlights and is the board on the left side). Plug in the power supply and take a voltage reading. If the voltage is near 12V then I suspect at least one of the inverter's Power Mosfets have shorted.

creakndale

 

[Preher TV]

You need to test the power adapter under a load, you can use a 24V automotive lamp, when connected to the output of the power adapter it should light instantly and stay lit no blinking and you should still have 12 volts(about) on the adapter even with the lamp connected.

Questions:

- Is the power supply really pushing out 5amps even though the voltage is correct? Does this matter?


Brad

Power adapters don't "push" current they allow current to be drawn, so the adapter allows 5A max current draw, if you hooked up a device to this adapter that only needs 2A @ 12V then it would draw 2A the power adapter would not push 5A into the device.

and yes it matters if the adapter has the correct voltage and allows for the rated current draw, a very common failure for these adapters is that the output voltage is fine when tested with a meter but fails under load. Often these powers adapters are easy to fix but sometimes it is not economical and you need to just buy a new one(power adapter that is).

 

[Preher TV]

It could definately be the power adapter....If this was an inverter board problem the TV would turn on possibly flash or just blank screen and then shut down, some older model LCDs without feedback circuits will power up just fine with a blank display. TV with no power is most likely a power supply , and I have seen many bad power adapters for LCDs.

also like creakndale said it is most likely not the DC power jack.