Proscan plded3992a-c led tv backlight failure?

[icekillah]

Just got this one in and wanted to get some experience in LED tvs. This tv has only one board doing everything power, main, led driver, all in one board! The symptoms are led light turns from red to blue when power button is pushed, the back-light comes on then immediately turns off, the light turns to full power once a second then immediately turns off again it will flicker once a second forever, the signals are fine it seems that the "mainboard" part is working properly. I focused on the led driver section on this board, there is 3 black wires and 3 red wires. Im assuming that the leds are wired in series and the red wires are the return paths from the panel (can this black/red combo be confirmed?) I have edited the photo of the led driver connector on this board to show the voltages one of the red wires is reading 0v while the other two are at 2.4v when the set is powered on, please consult the pics for all the voltage readings. Im assuming that there is a bad led somewhere on the 0v red wire's circuit and the panel is immediately turning off as a protection measure. If i were to cut the 0v red wire return path would the rest of the panel's back-light stay on? Are there any tricks to locating a shorted led? i have a bench-top power supply and am ready to strip down the tv to the leds in the panel.

[budm]

Re: Proscan plded3992a-c led tv backlight failure?

The LED strings may be connected in series or individual drive circuits. If they are in series there will be only one current sensing resistor and only one MOSFET for sinking current. I cannot see real well on the pictures to tell what the setup is. Most failure are due to open LED. It looks like it has 3 strings. Do you have good clear pictures of the bottom side?
I made this indicator to put in series with the wire to see if is show any current draw in the string, the voltage reading seems low but then again we do not know how LEDs there are in the string.
https://www.badcaps.net/forum/showpo...&postcount=107

What is the voltage rating on those two caps just right below the TOROID inductor for the Voltage booster circuit for the LED driver circuits?
I hope it is not EEPROM problem. There are more than one version of this model.
http://www.shopjimmy.com/catalogsear...scan+plded3992

[icekillah]

Re: Proscan plded3992a-c led tv backlight failure?

Ok the voltage rating for those caps are 100uf @ 63v pretty sure those are the ones you asked for, I took specs off all caps on the board and they are in one of the attached pictures.



I also took pics of the back of the board the eeprom looked damage free but there is a picture of the back of this "SUPER BOARD". There seems to be only one MOSFET that is hidden under a heatsink. also there seems to be a rather large voltage regulator. Is there any test i can do with my benchtop power supply and the red/black wires to the led strips? The voltage readings from the led driver we jumping around at 33v-40v wouldn't that be a giveaway that the leds are hooked up in series due to the changing voltage values? What is the next step, is it time to dismantle the panel and check led manually?

[icekillah]

Re: Proscan plded3992a-c led tv backlight failure?

Ok i thought i would update this post. I managed to remove the backlighting from the panel. got a nice cut from the sheet metal like material, now its personal this tv drew first blood! there are 3 horizontal strips with LEDs the middle would not light up at all, thats gotta be the offending hardware. so the strip is out but it looks like there is a glass bubble over the diodes, are they connected, or can i pop off these caps? I also noticed two test points marked "K" and "A". I have a benchtop power supply and would like to test each pad in series, until the culprit is found but i do not want to fry the hardware im assuming i should set it up for 2.5v and max out the amps. Please let me know if this is a bad idea as i cannot order this part. any idea where these led pads can be purchased? Enjoy the pics

[budm]

Re: Proscan plded3992a-c led tv backlight failure?

That looks almost the same setup as this one here:
All 3 strips are connected in series inside the panel instead of having 3 pairs of wire running out and connected in series out side the panel.
https://www.badcaps.net/forum/attach...0&d=1409431845
https://www.badcaps.net/forum/showpo...&postcount=107
White LED Vf (forward Voltage is about 3.1~4V), I would set the current limit to about 10mA at 3.5V. A is ANODE (+), K is CATHODE (-).
You can try using your meter is Diode mode test each LED to see if your meter can supply enough voltage to turn on the LED.

[icekillah]

Re: Proscan plded3992a-c led tv backlight failure?

budm you are a freakin Genius! you want my first born? you can have him I'll throw in my second born too! I was wrong they are not in series they are in parallel of course it was the last led i tested to be the culprit(the diode closest to the power in connector) your multimeter trick worked perfectly. I took a snapshot of the panel just for reference. Would you recommend the following leds as replacements? they say cool white which seems right but im not sure if they are powerful enough. the link is:

http://www.ebay.com/itm/100pcs-1210-...item20ebdc8760

[budm]

Re: Proscan plded3992a-c led tv backlight failure?

I am not sure if it will work, it does not have spec for the current rating, the lights output is Millicandela (mcd): 1900-2200.
The one in your picture looks close to what is shown on EBAY, but you should measure the dimension of what you have.
So when you turn it on that strip did not light up, but the other did light up for seconds before shutdown.
Do you have any rectifier diode such as 1N4XXX series? About 5 of them?
The 1210 spec for example:
http://lighthouseleds.com/plcc-2-121...ht-2500-m.html

The sad part about this repair is that one already failed so you can expect more to fail later on. I believe they failed due to poor heat dissipation, they do not last when they are over heated.
Some good reading about LED backlights.

[LiliMoM]

Re: Proscan plded3992a-c led tv backlight failure?

just a bit sideways of topic. So if this level of tinkering is beyond my ability. Is this issue with NO backlighting at all it seems on this same model my son has worth taking for a repair?

Or would it just be give it a try anyway and if no success then bite the $$$ and buy another one (which I am loathe to do)

???

[Ckirchj]

Re: Proscan plded3992a-c led tv backlight failure?

Icekillah - My 3 year old plded3992 just started having the exact same problem as yours (backlight LEDs flashing on/off). I was wondering what led replacement did you ended up using, and/or has anyone figured out where those OEM light strips could be purchased?

Thanks in advance.