Seiki SE32HY27 - No backlight on 2 system boards

[wyrmzr72]

Hello all,
I'm working on a Seiki SE32HY27 LED TV. It was most likely the victim of a power surge, at which point I had the user unplug it, and it went from no power to power with no back lights.
I replaced the board, since this unit has the main and power board integrated into one unit, and the first replacement gave me no power, just a red indicator light. So, I exchanged that for another, which is back to powering on, but still no back lights.
I'm getting a reading of 48 volts from the LED power when the TV is on, and 41 volts when it's off. This unit has 3 strips of 8 LEDs, and from what I've seen, a typical white LED needs somewhere around 3.3v to power on, which would give me 26.4 volts per strip, if my math is right.
Right now I'm leaning toward trying to test each strip, but assuming that 48 volts for one strip would be too much. I'm debating digging up an old laptop power supply to test each strip, hoping that one strip has become shorted. Since the laptop power supply is rated 19.6 volts (at least, most of the newer ones I've seen are), is this going to be enough to power a whole strip?
Quick edit: I tested the individual strips for resistance, and every one of them reads infinite. While I find it hard to believe all 3 strips would typically go out at once, I set my meter to 20M ohms and still get the same reading, so I'm thinking the entire set of strips is bad?

[wyrmzr72]

Re: Seiki SE32HY27 - No backlight on 2 system boards

And just for the record, these LED strips are not what I'm used to seeing; the back of the strip appears to ground to the TV itself, and if those small solder joints are test points, they're not working with a 3v power supply.
There are no solder joints on the back of the strips; just one solid piece of copper, with the occasional hole for a screw, or what may be some kind of "test point", which would actually just ground the strip to the back of the TV.

[cheeky2]

Re: Seiki SE32HY27 - No backlight on 2 system boards

I would suggest you read up about how to test leds as resistance of the led strips has no bearing as to the condition of the leds. If you do your homework then you will have your answer. Everything to find your answer is on the forum ie test the leds voltage with reference to the chassis ground of the TV and not across the two connections on the leds. No grounds are on the back of the strips that connect to the leds, it might have a copper strip on the back of the leds. Scratch the white paint off the front to test individually the leds.

[wyrmzr72]

Re: Seiki SE32HY27 - No backlight on 2 system boards

Thanks for that info. I was assuming that if power was supposed to go through the strips, then I'd have some continuity.
I'll try my 3v test and see if I get anything from scratching the paint off the painted wires. I did search the forums, and saw some people had luck with laptop power supplies, but knowing that 3v x 8 LEDs = 24v (probably slightly higher), I'm looking right now to see if I have a 24 or even 48v power supply (48v should let me test 2 strips at once, I'd think).

[dick_barton]

Re: Seiki SE32HY27 - No backlight on 2 system boards

When you power on does the led voltage jump initially to a high voltage and then drop just as quickly. If it does then this is normally indicative of led(s) problem. If your meter has min/max function then use that function to carry out the check.

[budm]

Re: Seiki SE32HY27 - No backlight on 2 system boards

https://www.badcaps.net/forum/attach...1&d=1570299612
1) Put all the connectors back in place.
2) Put the meter in DC mode 200VDC scale the attache the meter probes to each leg for the 47UF 160V CapXon cap, then turn the TV on while watching the meter, it should jumps to around 100VDC.
3) Remove LED connector and repeat step 2.
BTW, the L2 inductor is broken.

[wyrmzr72]

Re: Seiki SE32HY27 - No backlight on 2 system boards

OK, I tested the voltage across the cap, and it does jump to around 100v with or without the LEDs connected, and then drops right back down to the 48v range. So, looks like I've got some bad LEDs.
I am testing individual lights now after scraping paint off the circuits, and it appears the first strip has at least 2 bad LEDs. I'll continue checking the rest to see what I come up with.
Thanks for the help; it appears my search-fu just wasn't strong enough.

[budm]

Re: Seiki SE32HY27 - No backlight on 2 system boards

You may want to look into replacement strips and replace them as a set, once it is done then you need to turn down the backlights (not brightness) on all input to as low as possible to extend the life of the LED's.