How to test LED backlight without disassembly using 9V batteries

[@muhammadsyed7981]

Hi, you have presented an excellent video showing voltages to verify, I dont get backlight at all does that mean Power Board BN44-00667A is bad? I would really appreciate if you could guide.

[@RandomDIY09]

While it is possible that only parts of the power board stopped working, you should check if it produces any voltages. I would check if the TV’s status lights come on, and check if the TV produces an image. I connected a DVD player and shined a flashlight onto the panel - in my case I could see the movie but without backlight. If that works, power is likely not the problem. To make sure, find the connector from the power board. Very close to that connector your board might have test points which are labeled. This is what I measure in the beginning of the video. See if you get voltage there.

[@muhammadsyed7981]

Thanks a lot sir

[@geeks5048]

What is the measurement of the resistor you used? How did you know which resistor to use?

[@RandomDIY09]

Each strip has 14 LEDs, so with 3V per LED, that’s 42V total. My power supply was 45V, leaving 3V for the resistor. I aimed for 20mA, but I used a 100-ohm resistor since it was close enough, which gave me 30mA (using Ohm’s Law: R = 3V / 0.03A). For quick tests, you probably don’t even need a resistor if you’re just probing. Just be careful not to damage the LEDs if you’re testing for longer periods!

[@nickhaley1212]

What watt does the 100 ohm resistor have to be, 1/4 watt, 1 watt or does it not matter

[@garciatechnologyservices1633]

Good tutorial. I've seen a few others and all the techs explained there techniques very well, such as you did. But, here is the BUT... What are the common systems of having bad =LED lights/strips. l am a rookie tech so please forgive me if the question is too simple. Thanks for your video.

[@RandomDIY09]

The symptoms of bad LED strips is that your backlight is missing. If your TV turns on and stays black, shine a flashlight on the screen. If you see an image, everything on your TV works fine only the backlight is broken. Even if only one LED is bad, you won‘t have any backlight - that was the case with mine.

[@xiaolinhu3906]

Do you need a constant current board or a display backlight belt? We are the manufacturer.

[@irishguy200007]

What was the problem with the tv

[@RandomDIY09]

Screen stayed black after turning the TV on. Shining a flashlight onto the screen I could see images (used DVD as a video source). As the TV was producing pictures just fine, so I started checking voltages and found the issue with the backlight.

[@H.DotNet]

How do you come up with 5 batteries x 9 = 45v, not 3 batteries?

[@RandomDIY09]

I measured about 300V, divided by 5 light strips equals 60V. I felt 45V should be enough so I ended up using 5 batteries.

[@rkohland]

I have the exact same Samsung as yours with what appears to be the same LED strip out that you had in your video. But I believe each LED strip is made up of two sections, a 3A section and a 2A section. Which section of yours was out? Is there a way to determine this so as to not have to purchase both for the repair?

[@RandomDIY09]

In my case I opened it up and took the bad strip out. In fact the LEDs were all ok! I had a disconnect on the copper rails BETWEEN two LEDs of that bad strip. I bridged it with solder and was back in the game. When I took the panel apart I did not notice a difference in the strips, they all looked the same to me and they all seemed to be made out of one section. HTH.

[@superduperboyx]

@@RandomDIY09 Did you record a video taking out the bad strip and soldering it back?

[@hadireg]

nice way to test! Thanks for sharing. guess when only two wires go to the LED backlight we'll need more 9v batteries...

[@irishguy200007]

A shed load of them

[@dhoser9296]

Excellent video! Just what I've been looking for, how to test your strips without disassembly. Do you really need the 100ohm resister on the positive connector?

[@dhoser9296]

Just checked the back of my Panasonic TC-39AS530U and mine is setup differently. I don't have a connector like what you show going from the power board to the LED strips. I have a cable from the power board that splits and runs to the main board and also the LED driver board. From the main board I have the ribbon cable running to T-con board the two ribbon cables from that to the LED display...bummer...like your setup better. Guess I'll have to dissemble it and check the strips individually.

[@RandomDIY09]

The resistor is for limiting the current. LEDs are diodes and have very small internal resistance in "forward" direction which means the current is barely limited. Too much current could damage the LEDs and I rather played it safe than sorry. I wanted to fix the LED strips, not do any more damage! And it was quite handy to simply push the wire of the resistor into the connector :)

[@jerryo21]

@@RandomDIY09 couldnt you just use less batteries? (I have no idea how it works just curious) thanks

[@RandomDIY09]

@@jerryo21 It’s about the voltage in this case. I put them all in series, so the voltage of each battery adds up to the total voltage. You can probably get by with less.

[@Pendlm]

Thanks, just what I needed!

[@RixtronixLAB]

I have a symptom, I can get standby mode red LED, when I turn it on Green LED is on for about half second, backlight is on, but return to stand by mode again, is it backlight issue ? Nice video, thanks :)

[@RandomDIY09]

Don‘t think it is a problem with the backlight in your case. If TV is on and you can see the image with a flashlight pointing at the screen, it would be.

[@RixtronixLAB]

@@RandomDIY09 do you reckon, what's the issue? Thanks

[@RixtronixLAB]

@@RandomDIY09 Is it power supply problem for backlight LED ? How much is the voltage needed for backlight LED ? thanks

[@CR125Elsinore]

Without removing the panel, how do you know if all of the lights on each strip are working? Trying to determine if my power supply is bad or if I have a partial led outage. I’m getting backlight leds that are cycling from bright to dim on appx 3/4 of the screen.

[@RandomDIY09]

Each strip is a series of LEDs and multiple strips are also connected in series. If one LED is defect, the whole backlight will be off (like in my case, one LED was damaged all others were fine). So if you see light, I‘d say your backlight LED strips are not the problem.

[@irishguy200007]

Your strips are each in parallel??

[@eroticmasterbaker]

My backlight flashes on for a second when I power up then goes out. I removed the led strip and if I bend it I can get it to stay on. Can I fix that?

[@createspaceone]

i have only 4 wires on the ribbon power cable that power the two strips/sides on my lg, i actually tried this and realised mine would need a lot more than 45 volts to power up, im guessing i would need 10 or 11 of these batteries lol thanks! anyway. probably easier to buy a led tester.

[@alimuhammad.s3013]

How can these leds run on 45 volts instead of >200volts

[@broadcastblk]

Each strip is 45 V. You have 5 strips. 45 x 5 > 200 V

[@SlawKingOG]

@@broadcastblk nice explanation. thanks.

[@videobrownsville]

@@broadcastblk arent these 45volt strips in parallel? thats how you were able to light the strips at the connector.

[@wpgspecb]

What is the purpose of the resistor ?

[@RandomDIY09]

The resistor is for limiting the current.

[@wpgspecb]

@@RandomDIY09 I ran a bank of 9volts totaling 63 volts to 1 of 3 LED arrays on my TV and got no light. LEDS are known good.

[@sunildjbakori7275]

Nice sir

[@xiaolinhu3906]

Maybe you need a constant current board _! I'm a producer.

[@wolfgangboettcher3126]

Sorry I broken plasma

[@myethiopia6721]

Hi

[@balloney2175]

I really appreciate your effort, but you keep flipping the connector making it hard to understand the positive vs the negative.

[@UnacceptableViews]

he mentioned grey was the positive in this case. if in doubt use a multimeter to determine polarity on the power supply. even if it isn't producing enough to light the strips it will give out enough to determine polarity. cross reference the pinout on the board to that of the strip connector

[@RandomDIY09]

I like to help. You are talking about the 9V battery test? The positive is connected to the resistor and it goes (on my TV) into pin hole 1, 3, etc. the negative goes always into the adjacent pin, i.e. 2, 4, etc. So: 1 is + 2 is - // 3 is + 4 is - // and so on. Each LED strip is connected in series. If one LED is blown, the complete strip won‘t light up. Then, all light strips are connected in series again. So you could have only one bad strip causing the complete backlight to fail. The test with the 9V batteries tells me which LED strip(s) are bad. Only reason I am flipping the connector is easier access to the pin. HTH.

[@balloney2175]

@@RandomDIY09 Thanks a lot! I already bought the led tester before learning from you. I find out that each strip which has 6 LEDs, should be at least 16.3 volts. The bad ones has only 4.5 volts. So I replaced the bad ones, now my TV is working. Your awesome idea can be applied to other projects I am thinking. Thanks, again!