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

[knappster]

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

Thanks for all of the advice. Time is at a premium with a two year old running around the house, but I am hoping to try to disassemble this while the little one is running around tomorrow. I will follow-up once I have checked it out. Could be tomorrow, could be in a couple weeks.

[knappster]

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

Alright, I got everything torn down and powered it on with just the inverters connected to power and all 16 lights came on for the couple seconds, then went off again. I have a screenshot of a video I took of the lights coming on that I've attached. I have also attached a couple photos of a capacitor on the power supply that looks a little bulgy and a photo of the model of capacitor on the inverters. The power supply cap may explain the issues I was having previously with the power sometimes acting up when turning the TV off? For the backlight, is it enough evidence to say that it is definitely one of the inverter modules? I could try replacing the 8 caps and if that does not resolve it do I get a master/slave pair and just replace them? Thanks again guys.

[dick_barton]

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

I think at this point if my memory serves me correctly that you take BL_ON up to 5V to keep the lamps on. Please correct me if I'm wrong and need to do it via a resistor.

[CapLeaker]

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

I could try replacing the 8 caps and if that does not resolve it do I get a master/slave pair and just replace them? Thanks again guys.

I'd replace those caps and get the inverter for that side that doesn't light up.

[budm]

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

You only have one working Inverter board another is not working, it is Master/Slave Inverters for push-pull lamp driver setup, so check the Slave inverter board fuse and the MOSFETs too before replacing the bad caps.

[knappster]

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

I think at this point if my memory serves me correctly that you take BL_ON up to 5V to keep the lamps on. Please correct me if I'm wrong and need to do it via a resistor.

Is this the same as the "BON" pin on the power supply? It is already reading 5V.

[knappster]

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

I'd replace those caps and get the inverter for that side that doesn't light up.

I'm not sure if the picture is misleading... when I was watching in person, I didn't notice only one side lighting up. When I watch the video again, it appears that the entire thing comes on brightly, then the light moves to the right... this may just be the camera adjusting for the brightness though. Is it possible for just half of a CCFL to light up? Is there anyway to upload the video so that you can view it?

[knappster]

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

You only have one working Inverter board another is not working, it is Master/Slave Inverters for push-pull lamp driver setup, so check the Slave inverter board fuse and the MOSFETs too before replacing the bad caps.

I tested all of the little white fuses in the beginning and did not find any issues. Are there more fuses I should be checking for? And can you point me to a guide on testing the MOSFETs? Sorry, I've searched a bit here and on google and haven't really found anything specific to the application.

[CapLeaker]

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

I'm not sure if the picture is misleading... when I was watching in person, I didn't notice only one side lighting up. When I watch the video again, it appears that the entire thing comes on brightly, then the light moves to the right... this may just be the camera adjusting for the brightness though. Is it possible for just half of a CCFL to light up? Is there anyway to upload the video so that you can view it?

put a vid on youtube and post the link?

[knappster]

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

How about google drive? Does this video help?

https://drive.google.com/file/d/0B5M...ew?usp=sharing

[CapLeaker]

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

Can we get hi resolution, straight shot pics of the inverters?

[knappster]

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

Can we get hi resolution, straight shot pics of the inverters?

I will try to get these photos this weekend. Are there any specific components you may want to see closeups of?

[knappster]

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

Alright, well I was unable to track down my digital camera, so I did the best I could with my cell phone camera. I have 3 pictures of each board. One of the entire board, and then top half and bottom half of each board. Hopefully this has the detail that you need. If not, I can try again when I get the free time.

I may have some more challenges ahead, though. I just plugged the TV in for the first time since I stripped it all down to ensure that I was still getting the "Please Wait..." LCD display, and I am not. So that means one of 3 things:
1) The backlights are turning off more quickly now.
2) I did not get the LCD screen plugged back in properly
3) I damaged something else while disassembling/reassembling everything.

Depending on the next steps required to diagnose the backlight, I may need to check everything with the LCD so that I don't end up with a TV that has a backlight, but no LCD, lol. Anyway, let me know what you think when you get a chance to review the photos. Thanks!

[CapLeaker]

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

Now we need measurements again on the power supply where it goes from it to the main board. Take the DCV readings incl. the pinout name and post it.

[knappster]

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

Now we need measurements again on the power supply where it goes from it to the main board. Take the DCV readings incl. the pinout name and post it.

Okay, I have confirmed the LCD and audio still works by plugging it into an HDMI source. I have taken the readings you requested again. I think i must have omitted one of the cables last time, but the results of it did not seem unusual. I think there is one more cable that is going from the PSU to one of the inverter boards. Do you need that measurement as well?

PON: 3.0
GND: 0
5V: 5.1
GND: 0
GND: 0
16V: 15.8
16V: 15.8
GND: 0
5V: 5.0
GND: 0
5V: 8.8
32V: 32.0

BON: 5.0
PWM: 3.3
GND: 0
GND: 0
GND: 0
24V: 23.7
24V: 23.7
24V: 23.7

BON: 5.0
PWM: 3.3
GND: 0
GND: 0
GND: 0
GND: 0
24V: 24.2
24V: 24.2
24V: 24.2
24V: 24.2


I think I mentioned this the first time posting, but one of the 5V outputs is reading 8.8. Is that a sign of an issue on the power supply?

Since BON is high, is my best option going to be to replace the master/slave combination for $60? Or is there still a risk that something else is the problem?

[knappster]

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

budm, I haven't seen you respond since I posted the video. I just wanted to ensure that the photo was not misleading. Is your diagnosis still the same? Thanks for the feedback.

[budm]

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

It looks like only one Inverter board is working.

[CapLeaker]

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

You should be fine by changing the inverter boards.

[knappster]

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

Thanks guys. I will give that a try and let you know what happens.

[knappster]

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

Thanks for the help guys! I first replaced the slave inverter with no improvement. Next I replaced the master inverter and it seems to be working just fine now. I took a photo of the screen lit up and I also took a photo of the back of the bad master inverter. I suppose the discoloration might give some indication where the failed component(s) is/are. So I probably now have a spare slave inverter as well. Thanks again.