Dynex DX-LCD42HD-09 goes blank after a few seconds

[knappster]

I have a Dynex DX-LCD42HD-09. When initially plugged into the outlet, the red LED comes on. When turned on, the red LED turns green and the backlight comes on and the "Please Wait..." white text appears for about 1 second before the screen goes blank and the backlight goes out. The power LED remains green until I press the power button again. About a year prior to this, the TV was working completely normally except for one annoyance. On occasion, when the TV was powered off, the green LED would turn red (which is normal) then about 15 seconds later it would turn green again even though the TV was still off. It would remain in this state until the power to the TV was unplugged and plugged back in. I have not seen any obviously damaged electrical components and am not particularly interested in diagnosing this on the component level so long as I can order a replacement board with some level of confidence that it will resolve the issue. If that's not possible, it is off to the scrap yard I think.

[knappster]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

Maybe I didn't provide enough information initially. I have taken photos of the main circuits that I could find. If there is any additional information that I can provide to assist in tracking down the fault, please let me know.

[CapLeaker]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

On the power supply measure all the DC voltages on all pins that go from it to the main board (2 ribbon cables) post them voltages including with the pin name you measured it from with the tv on.
Also try to set it to a channel or play a DVD etc, to see if it puts out audio and video. You have to shine a good flash light into the screen and you may see a picture.

[budm]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

Ahh the CMO inverter board. Check the resistance of the HV windings (there are two HV windings per each transformer:S1-S2, S3-S4 on each of the Inverter transformers (all 8) to see if they are within 3% from each others.
There are 4 white fuses that should be check also, those 4 black filter caps should also be replaced.
http://lcdparts.net/TransformerDetai...ProductID=2739

[ReeceyBurger123]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

Check the fuses on that inveter ! I have that inverter in atm on the master one the little fuse that is for the driver fet blows and the fet on mine was shorted.

[knappster]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

On the power supply measure all the DC voltages on all pins that go from it to the main board (2 ribbon cables) post them voltages including with the pin name you measured it from with the tv on.
Also try to set it to a channel or play a DVD etc, to see if it puts out audio and video. You have to shine a good flash light into the screen and you may see a picture.

One of the ribbon cables:
PON: 3.0
GND: 0
5V: 5.1
GND: 0
GND: 0
16V: 15.8
16V: 15.8
GND: 0
5V: 5.1
GND: 0
5V: 8.8
GND: 0
32V: 32

The other ribbon cable:
BON: 5.0
PWM: 3.3
GND: 0
GND: 0
GND: 0
GND: 0
GND: 0
24V: 24.2
24V: 24.2
24V: 24.2
24V: 24.2

I have confirmed that it has both audio and video on HDMI input 1, but the video was extremely hard to see (using my cell phone as a flashlight). I see that the last 5V signal on the first ribbon cable was supposed to be 5V but was all the way up at 8.8V so that does not seem good. Thanks in advance for any advice based on these results. BTW, I measured it from the grounded metal chassis of the TV.

[knappster]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

Ahh the CMO inverter board. Check the resistance of the HV windings (there are two HV windings per each transformer:S1-S2, S3-S4 on each of the Inverter transformers (all 8) to see if they are within 3% from each others.
There are 4 white fuses that should be check also, those 4 black filter caps should also be replaced.
http://lcdparts.net/TransformerDetai...ProductID=2739

Thanks for the response. I checked 4 fuses on each of the two inverter boards. They all tested okay (short circuit). The resistance of the windings all read between 1.052k and 1.079k so that falls within the 3% you suggested. I have not replaced any capacitors yet, because I first wanted to get additional feedback based on the information provided to you and CapLeaker if you think that might be the issue or if it is likely to be something else. Thanks.

[budm]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

All the voltages and the command signals for the inveter are present, so it it either the inverter board or the lamps.

[CapLeaker]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

Main board and PSU is fine. The problem must be on the inverters, wiring, cold solder joints, capacitors, or ccfl.
Just to confirm: BON = 5V and the backlights are off?

[Gootch46]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

Hi there I had this exact problem come across same tv
Once the fix I did was took tv all the way down to the bulbs and they were popped out of the inverter and had to be pushed back in and Wallah! Fixed so the tv was seeing more than one bulb out and shutting down. Good luck

[knappster]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

Main board and PSU is fine. The problem must be on the inverters, wiring, cold solder joints, capacitors, or ccfl.
Just to confirm: BON = 5V and the backlights are off?

That is correct. When I turn the power on, the backlights do come on for a few seconds, then go out. The measurements were all taken with power on, but the backlights had already gone out.

[CapLeaker]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

O.k. so it has to be the inverter(s) or the lamps or something between them 2.

[knappster]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

Hi there I had this exact problem come across same tv
Once the fix I did was took tv all the way down to the bulbs and they were popped out of the inverter and had to be pushed back in and Wallah! Fixed so the tv was seeing more than one bulb out and shutting down. Good luck

Thanks for the response. Is there any trick to getting to the bulbs? Based on everything you guys have said I wonder if maybe a bulb burned out and needs to be replaced. However, I imagine it is not a simple task to get to the backlights.

[vinceroger69]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

Everyone has there own diffrent ways of stripping down to lamps/leds some leave the boards on others do a full removal this is just one video showing a stripdown to give you some idea.
https://www.youtube.com/watch?v=EO2gHBJCvH0

[CapLeaker]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

You have to tear the whole LCD panel down to get to the back lights. So before I would even think on opening up the panel, I make sure to exhaust all other options.

when the back light is on, is there an area where the screen is darker? Basically you have to make sure that all lamps are lit evenly.

I am not saying it is a lamp problem yet, most of the time it is either the caps or the transformer on the inverter(s).

[knappster]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

You have to tear the whole LCD panel down to get to the back lights. So before I would even think on opening up the panel, I make sure to exhaust all other options.

when the back light is on, is there an area where the screen is darker? Basically you have to make sure that all lamps are lit evenly.

I am not saying it is a lamp problem yet, most of the time it is either the caps or the transformer on the inverter(s).

Unfortunately, when the backlight kicks on, the screen is black with just some text saying "Please Wait..." and only lasts a few seconds so I'm not sure I will be able to see if there is a darker region unless it happens to be where the text is. Next time I get back to it, I will try to look closer. Are there any tips on testing the caps and transformers or do you typically just start replacing components? It looks like I could simply buy the master/slave inverter pair to replace the entire boards at a reasonable price, but I don't want to do that and find that it was a bulb all along. Thanks for all of the help.

[CapLeaker]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

There are some CCFL testers, but not worth getting for a one time shot. Depending on inverters, you may be able to disable the protection circuit. Read the stickies there are some IC's mentioned on how to do that. You also can let the TV boot up, disconnect the BLon pin then reconnect it and see the screen again for 2 seconds.

[Gootch46]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

It's really not as scary as it sounds to tear it down , besides setting a cpl hours aside to do it its really noit that difficult. Once you get the plastic that surrounds it off you just need to separate the metal enclosure and then make sure you get the sheets of plastic in order but really not too bad. Then you will see on the right hand side I believe that the lights have popped loose out of the inverter push them back in and tv will come on. walla then opposite to get back together

[budm]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

Take really good pictures and notes while disassembling the panel just in case you forget how it goes back together.

[Gootch46]

Re: Dynex DX-LCD42HD-09 goes blank after a few seconds

Great idea Budm, let us know how this works out for you also knappster, Hope it all goes well for you.