Seiki SE47FY19 - No backlights

[budm]

Re: Seiki SE47FY19 - No backlights

The set of LEDs that light up probably has shorted LEDs, I can see brownish color on the LED LENS that is why that set lights up.
The other set of LED that does not light up may have open LEDs.

[MEB]

Re: Seiki SE47FY19 - No backlights

Sorry, the mystery picture is one of four little supports that keep the center of the screen from sagging in the middle towards the backlights, Kinda like the little thing pizza hut puts in the delivery box to keep the cardboard off the pizza. I broke one of them getting it out to remove the reflector. I guess I will have to glue it back in when the time comes?

I will try to trace some things around those strips and see if I can find out anything and get back to you. Thanks for all your help.

[MEB]

Re: Seiki SE47FY19 - No backlights

Just got through a long discovery session. I figured out how to test individual LEDs, sections of strings and if I had enough voltage I could test entire strings at the same time. Nothing a 1st grader couldn't do, but I am very excited just the same. I guess I am easily entertained. You were exactly right in your above circling identification of the condition of the LEDs. I will be back. Am taking the kids and grandkid to see my Mom/Grandma/Great Grandma in a few hours so have to give up for now. Thanks budm!

[MEB]

Re: Seiki SE47FY19 - No backlights

Have searched everywhere for LED strips. This is my first attempt at LED backlit TV so am sure I am in the process of doing what everyone else has already done. If I were to replace all of them, 2 strings of 6 sections for a total of 54 LEDs, best I can find would be over $100. That is something I would and will do, because I can't control the urge to fix something when I start, but that leads me to the second thought that I am again sure all of you have/had is why can't I just repair them for a fraction of the cost? So I have begun down that road. I have searched here and just scratched the surface, but would be interested to hear the tales from those who have already been down that road and might wish to share their feelings on the subject. It is not that I have unlimited time to spend, but I have more time than money and wonder if it is worth the effort. Would appreciate words of wisdom or directions to threads on subject. Right now, i have read budm mention 3V and 100mA so that is my starting point!

[budm]

Re: Seiki SE47FY19 - No backlights

https://www.badcaps.net/forum/showpo...&postcount=219
https://www.badcaps.net/forum/showpo...0&postcount=31

[MEB]

Re: Seiki SE47FY19 - No backlights

Thanks budm, one place I failed to look!

[MEB]

Re: Seiki SE47FY19 - No backlights

Man, I have been totally swamped at work and had to set my toys aside for a few months, but wanted to report back. I ended up going with Vishay VLMW51N2P3, PLCC2 Plus LEDs for my 1st attempt at fixing LED strips. They were kind of pricey at $1 each, but if it works out, I will try some cheaper ones next time. I need to practice and refine my methods but I have 1 strip done and I think they are a good match. Problems I have encountered is I am discoloring the surface coating of the strip removing with a heat gun and haven't done much better with a soldering iron so looking for ideas. I have been getting them back on with the use of a small amount of solder paste under the LEDs, but I have many more to do and will get back if I can improve my method. I have enclosed a picture of the old and the new.

[MEB]

Re: Seiki SE47FY19 - No backlights

Wow. I have been under a rock! I just saw ReeceyBurger123s video on YouTube and have saved myself months of experimenting with these LEDs. Lots of great stuff there!!!!

[ReeceyBurger123]

Re: Seiki SE47FY19 - No backlights

Awesome glad to help

[MEB]

Re: Seiki SE47FY19 - No backlights

OK, just got time to work on this set again. As of last time, I had bad leds, open and shorted and had identified them by individually testing and testing strings. I had ordered leds as stated in post 22, but never got back to it. Last night I decided to replace all 54 SMD leds and had a good time doing so. Now not so good. I tested all the strips with a DC power supply and all lit. I was applying 27 volts to each set of strings of 9 leds and all seemed well. I put them in the display and fired it up. The power supply contains 2 led connections, each for 27 leds. The 3 upper strings will light, the 3 lower strings would not. I assumed power supply problem so switched connectors to board swapping upper to lower set of strings. Now the lower set lit, so I still assumed power supply problem to one set of strings. But letting the set of strings (3 sets of 9 =27 leds) run for about 2 minutes, the lit ones started failing rapidly and randomly by turning blue and fading away till I powered the thing off. Removing and testing again with power supply confirms they got cooked! What have I done? 6 of the 27 which lit are now barely functioning. I have included the data sheet from the diodes I used. I am sure I did something stupid as this was my first LED backlit adventure. Be gentle please.

[MEB]

Re: Seiki SE47FY19 - No backlights

OK, still at it. I figured chances were good that I screwed up along the way in replacing all those leds so I ordered another set of strings from ebay. I know this set isn't worth much but I need to know. From the attached, there are 2 connectors in the upper right corner CON6 and CON8. The upper, CON6 drives the upper set of strips and the CON8 drives the lower. By swapping the sets of strings at these connectors, the CON6 correctly drives both sets of strings, but the strings attached to CON8 barely light, so I am thinking that means that portion of the power supply/inverter board is defective. With black to chassis CON6 LED+ is 106V and LED- is .6V, at CON8 LED+ is 106V but LED- is over 40V regardless of which set of strings is plugged into it. So I think the led strings are ok and I have a board issue, but don't know where to head next. I am being drawn to those 4 diodes in the lower right, thinking 2 might be for each set of strings, but I am guessing. This is my first led tv. Would appreciate some direction.

[dick_barton]

Re: Seiki SE47FY19 - No backlights

The operating current is probably to low at 180mA. Can you check the current flowing when you power up some of the original ones and compare.

[MEB]

Re: Seiki SE47FY19 - No backlights

Thanks for your reply. Using a clamp type probe cause I didn't want to have to rig up a way to break the circuit, a good set of strips connected to CON6 yielded approximately 500mA. Using the same strips connected to CON8 yielded 140-160mA. I know this isn't very accurate, but maybe it will help. Thanks.

[budm]

Re: Seiki SE47FY19 - No backlights

500ma sounds like you have some shorted out LEDs on that strip that is why it very important reason to use power supply with current limiter, 500mA though the LEDs on that strip can easily damage the good LEDs on that strip it is way above typical LED current handling spec.

[MEB]

Re: Seiki SE47FY19 - No backlights

Thanks, you said on post 4 that I could use a "60V variable" power supply. What would be a reasonable current limit to set for a string of 9 at 27V? More like 150mA?

[budm]

Re: Seiki SE47FY19 - No backlights

Post 4: "You can get Variable bench power supply that can do up to 60V or so with current limiter function for testing the LED strips." I sure did.
I start with 50mA first.
One thing to remember too that the strip with shorted LEDs will still light up but you have to look at the screen to see if you have dark spot on the screen due to shorted LEDs, or you can look at the total Vf of the LED strip to tell you how many working LEDs you have on the strip.

[MEB]

Re: Seiki SE47FY19 - No backlights

Thank you. I will report back.

[MEB]

Re: Seiki SE47FY19 - No backlights

I am totally confused. I got a variable DC power supply and set it for 27V and 50mA. Applying the proper polarity to each strip of 9 leds, lit them all fairly brightly. The power supply readings displayed 25.5VDC and 47mA on every strip of 9 so I am assuming that is good? All 6 strips of 9 leds lit up and looked good to me. I went back to using the clamp meter on the wires coming from CON6 and CON8 and readings were again like before, so I cut the white wires to each set of strips. With voltmeter in DC A max 10A I got .671A on the upper set of strings and in 400mA max .04mA on the lower set with the TV supplying the drive (I think the clamp meter couldn't read that low and I misread the initial reading. The upper set of strings (3 strips/27 leds) are very bright and the bottom set barely emit. I went back and changed the top strips to the bottom circuit and vice versus and everything repeated as stated. I must be doing something terribly wrong, but I can't see what. In my humble reasoning the strips are fine?

[MEB]

Re: Seiki SE47FY19 - No backlights

It seems the overcurrent situation from the power supply may have caused the destruction of the original repaired leds and will soon destroy the replaced strips. If it is the power supply, what should I check which could cause the situation of over current on one string and undercurrent on the other. Or am I completely wrong in my assessment?

[MEB]

Re: Seiki SE47FY19 - No backlights

As said this is my first attempt with LEDs. Decided to go back to basics and read. Starting to understand Vc, Vf and the use of current limiting resistance in examples with LEDs and physical wiring in example test circuit, but I am unable to relate it to the real world LED strip examples in TVs. I need a slight push in understanding where the current limiting comes to play in a TV. It must be incorporated in each strip or on the power supply/driver circuitry, but I see nothing on the strips. One driver to one set of strings seems to have little current limiting thus I am getting excessive current to that string, the other driver has little current, but if I swap the strings physically to the 2 drive connectors, the over current does not follow the strings which would indicate to me LED problems on those strings. If the current limiting is part of the power supply circuit on the board, it kind of makes sense. I need some enlightenment, then maybe I can fumble through this. Thanks.