Dynex dx-48d510na15 NO BACKLIGHT

[kgavionics]

Hi guys
i have a Dynex dx-48d510na15 which got picture, but no back-light at all.
i took the tv apart and i measured the voltage between the LED+ pin to the ground i found 99.5V (i have the same voltage with the connector pulled off)
Now, the problem, i didn't find any service manual for this tv.
Can someone tell me if LED voltage is good?
i appreciate all of your inputs guys
thanks in advance

[budm]

Re: Dynex dx-48d510na15 NO BACKLIGHT

You need to leave the black probe on the chassis and the red probe on the LED+ pin and then turn on the TV while keeping an eye on the meter to see how high the Voltage jumps up to before settling down to 99V, it should jump much higher than 99V.
We also need the straight shot pictures on the whole bottom side of that power supply board.
BTW, are two of the pins labeled with LED+

[kgavionics]

Re: Dynex dx-48d510na15 NO BACKLIGHT

Thank you budm for the prompt reply
first, to answer your question, the 2 middle pins are labeled LED+ and the two outer pins are labeled LED-.
I measured the voltage when tv powers up, and the voltage goes up to 158Vdc for a fraction of second ( i used the MIN-Max function on my multi-meter).

[budm]

Re: Dynex dx-48d510na15 NO BACKLIGHT

That means the Voltage boost converter is working but it does not see the load so the Voltage went up high which causes the over Voltage protection to kicks. The 99V is the feeding Voltage to the Boost converter circuit.
You have open circuit in the LED circuit some where, more likely open LED, or open connection.
Do the same test again on each one of the LED - then we may be able to tell which LED string has open circuit. I still need the pictures of the bottom side of the board.

[kgavionics]

Re: Dynex dx-48d510na15 NO BACKLIGHT

Both Led- are 0.04Vdc and they go high to 0.07Vdc when the tv powers on.
Btw. I uploaded the bottom side of the psb.

[budm]

Re: Dynex dx-48d510na15 NO BACKLIGHT

OK, you have two sets of LED strings and they are connected in parallel (when one string goes open circuit, the constant current will be forced on the good string until it will burn out the good string), the LED+ is connected to the Anode of the both LED string, the LED - are the Cathode return of the LED strings. At this point your reading of 0.04/0.07VDC indicates open circuits in both LED strings.
I cannot read the barcode sticker to see what the model number of the LCD panel is.

[kgavionics]

Re: Dynex dx-48d510na15 NO BACKLIGHT

So both Led strings are dead?

[budm]

Re: Dynex dx-48d510na15 NO BACKLIGHT

Based on your Voltage readings on the LED -, yes, you have open circuit in the LED string some where. You will need to trace out the connection from the power supply board all the way to the LED strip.

[kgavionics]

Re: Dynex dx-48d510na15 NO BACKLIGHT

Thanks budm for your help.do you know how many Led strip this Tv has? I didn't do a complete teardown yet!!

[budm]

Re: Dynex dx-48d510na15 NO BACKLIGHT

I cannot find the spec sheet of that LCD panel, and no luck finding out what the LED strips look like either.

[kgavionics]

Re: Dynex dx-48d510na15 NO BACKLIGHT

Apparently, this tv has 10 Led strips, i've looked online and either the price is too high or they are out of stock.Is there a generic Led strips that can order to fix the problem?