Seiki 50 inch has no back light

[bluedawg]

Re: Seiki 50 inch has no back light

Still needing help if anyone is available. my last 3 post on this thread should explain where I am stuck at. The only problem with tv is no backlights

[gvrayden]

Re: Seiki 50 inch has no back light

Still needing help if anyone is available. my last 3 post on this thread should explain where I am stuck at. The only problem with tv is no backlights

bluedawg, did you solve the problem ?
I have the exact same model and no backlight, I did the flashlight test and able to see images and also hear sound.

[budm]

Re: Seiki 50 inch has no back light

Mr Budm Now that I replaced power board I can tell you I have 5volts dc going to BL pin on powerboard and I have power on red and white wire connector 1 for back lights and power on red only wire on conector 2 for BL and no power on other 3 connectors . I think it was like 240 on 1st connector red wire and 120 on white wire 1st connector and 88 on red wire on 2nd connector. Hope this helps you help me.

That tells me you have open circuit in the LED strips some where due to bad connections or open LED/s.
It looks like it has 5 strings of LEDs and they are connected in series to form one long string.

[bluedawg]

Re: Seiki 50 inch has no back light

Wow thank u . I just trashed the set this weekend . I give up but what u said helped me to kno what i suspected but had no way to verify. Would there had been a way to fix it or would it not had been worth the time and labor and thank you in advance

[budm]

Re: Seiki 50 inch has no back light

The hard part will be taking the panel apart to get to the LEDs and try to find the replacement LEDs for it. If you get the new TV with LED backlights, you should go to the user setup and turn down the backlights level to as low as you can, this will extend the life of the LEDs and it will run cooler.

[electronicsurplus]

Re: Seiki 50 inch has no back light

Is there any way to bypass a string of leds ?

Perhaps using diodes or Resistors?

There are 14 leds in each strip and 5 rows

Thinking each led uses approx 3 volts each equals 210 volts

Any ideas would be greatly appreciated

Thanks much

[CapLeaker]

Re: Seiki 50 inch has no back light

LED's are regulated on constant current, not on voltage. Why would you want to bypass a whole string of LEDs anyway? Then you'd have an area that isn't back light. How much LED's are out?

[budm]

Re: Seiki 50 inch has no back light

Is there any way to bypass a string of leds ?

Perhaps using diodes or Resistors?

There are 14 leds in each strip and 5 rows

Thinking each led uses approx 3 volts each equals 210 volts

Any ideas would be greatly appreciated

Thanks much

Did you verify that the LED strings are connected in SERIES to form one string?

[electronicsurplus]

Re: Seiki 50 inch has no back light

They are actually all individual strips of 16 Leds with 2 wires going to Power Supply for each strip

I powered each strip using approx 40 V DC and, all strips lit properly except 1 strip. The TV also functioned and actually had a picture using the external power supply. of course I could only light one strip at a time and the picture was obviously dark but nonetheless working

After opening the screen I found that there was 1/2 of one of the strips was obviously burnt. Also, since they are split into 2 separate strips. After testing each 1/2 only one of the sections was actually burnt

Checking the power supply for voltages and, checking each + & - points on the connector there was 0 volts. However, If I tested the 1st connector and using the panel as - ground I found 120 volts on the 1st pin

So, I think somehow the Power Supply may be powering the strips in series format for whatever reason since, they do seem more than adequate brightness when lit individually.

My question is. Is there any was to isolate or remove the defective strip. because,There are many Leds in the screen which will more than sufficiently light the screen to be usable. We could of course simply replace the Led strip or, at least the defective section. Or, Piggyback individual Leds since, We do have several 100's of available strip assemblies. Which are also available to any of the Members on this site for free. We will make a list of all the Part #'s in stock. We also, have several 1,000 T-Con boards available. Since, we have closed our Replacement TV Parts warehouse thanks to our neighbor W-Mart's prices which we could not compete. So, we are now stuck with 1,000's & 1,000's of remaining small ONLY parts (NO Power Supplies or other boards. (we would only ask for shipping costs Typically less than $5.)

We have already scrapped 10's of 1,000's of boards due to space restrictions. But, we retained many small parts that require little space and, are available.

But, We are more interested to learn and share that information which I am sure many others here are having similar problems without ever needing to split the screens (which most times results in cracking the screen.)

We actually donate many of these TVs to the less privileged while at the same time gaining some experience working with Leds. and at the same time sharing that information with others that will benefit

Also, not fully understanding exactly how this Power Supply operates in the Led power section made me wonder if it were actually the power supply but, we purchased a working power supply and, it did not work either. Again, the TV does turn on and off and functions somewhat normal except for the backlighting

Any help would be greatly appreciated or, direction as to how exactly Leds function

[electronicsurplus]

Re: Seiki 50 inch has no back light

I found this but, it is very confusing

[budm]

Re: Seiki 50 inch has no back light

They are actually all individual strips of 16 Leds with 2 wires going to Power Supply for each strip

I powered each strip using approx 40 V DC and, all strips lit properly except 1 strip. The TV also functioned and actually had a picture using the external power supply. of course I could only light one strip at a time and the picture was obviously dark but nonetheless working

After opening the screen I found that there was 1/2 of one of the strips was obviously burnt. Also, since they are split into 2 separate strips. After testing each 1/2 only one of the sections was actually burnt

Checking the power supply for voltages and, checking each + & - points on the connector there was 0 volts. However, If I tested the 1st connector and using the panel as - ground I found 120 volts on the 1st pin

So, I think somehow the Power Supply may be powering the strips in series format for whatever reason since, they do seem more than adequate brightness when lit individually.

My question is. Is there any was to isolate or remove the defective strip. because,There are many Leds in the screen which will more than sufficiently light the screen to be usable. We could of course simply replace the Led strip or, at least the defective section. Or, Piggyback individual Leds since, We do have several 100's of available strip assemblies. Which are also available to any of the Members on this site for free. We will make a list of all the Part #'s in stock. We also, have several 1,000 T-Con boards available. Since, we have closed our Replacement TV Parts warehouse thanks to our neighbor W-Mart's prices which we could not compete. So, we are now stuck with 1,000's & 1,000's of remaining small ONLY parts (NO Power Supplies or other boards. (we would only ask for shipping costs Typically less than $5.)

We have already scrapped 10's of 1,000's of boards due to space restrictions. But, we retained many small parts that require little space and, are available.

But, We are more interested to learn and share that information which I am sure many others here are having similar problems without ever needing to split the screens (which most times results in cracking the screen.)

We actually donate many of these TVs to the less privileged while at the same time gaining some experience working with Leds. and at the same time sharing that information with others that will benefit

Also, not fully understanding exactly how this Power Supply operates in the Led power section made me wonder if it were actually the power supply but, we purchased a working power supply and, it did not work either. Again, the TV does turn on and off and functions somewhat normal except for the backlighting

Any help would be greatly appreciated or, direction as to how exactly Leds function

All the wires from the LED strips come back to the LED driver section of the power supply/driver board, the problem is, you need to know if those wires from the LED strips are terminated as one series connection or each strip may be driven by individual LED driver. You have to look at the LED driver section to find out how the Cathode return wire of each LED strip is connected to.
If you use one of those LED tester such as the one sold by shojimmy, the LED strip that has shorted LED will still light up, so it is important to read the Vf Voltage as shown on the tester and compare it to the other strip (with same LED setup). The Vf will tell you if one or more of the LEDs have shorted out or not. You can use 2W 3.3V connected in reverse bias in place of a LED, I use 5 1N4007 (I have lots of them) is series and connected in forward bias in place of the bad LED (the diode will get quite warm).
https://en.wikipedia.org/wiki/LED-backlit_LCD

"direction as to how exactly Leds function"
https://en.wikipedia.org/wiki/Light-emitting_diode

Want to learn?

https://cdn.badcaps-static.com/pdfs/...5b3e53eac5.pdf
https://www.maximintegrated.com/en/a...ex.mvp/id/4384

[electronicsurplus]

Re: Seiki 50 inch has no back light

Beautiful. I will be doing a bunch of reading today. Thanks a bunch

So, the Led tester will still light the strip even though there are one or more bad Leds in the strip? I always thought of them as in series Meaning. much like Old Xmas lights once one goes bad the whole string goes bad

I will be ordering one of those testers today.

Also, is there any way to also test the Power Supply itself ? since, it does appear to be working properly except for the Back lighting. In other words, how to test if it is putting out sufficient or any back lighting voltages at all

Thanks again

[electronicsurplus]

Re: Seiki 50 inch has no back light

This is one of the ways we currently use and convert some televisions just for fun


https://www.youtube.com/watch?v=X6Frth0F5x0

[budm]

Re: Seiki 50 inch has no back light

Beautiful. I will be doing a bunch of reading today. Thanks a bunch

So, the Led tester will still light the strip even though there are one or more bad Leds in the strip? I always thought of them as in series Meaning. much like Old Xmas lights once one goes bad the whole string goes bad

I will be ordering one of those testers today.

Also, is there any way to also test the Power Supply itself ? since, it does appear to be working properly except for the Back lighting. In other words, how to test if it is putting out sufficient or any back lighting voltages at all

Thanks again

If one of the LED in the string is shorted out then the circuit can still complete the circuit, the current will just flow through the shorted out device. If the LED goes open circuit then the string will not light up.
I.E. 3V per LED, 3 LEDs in series so total Vf = 9V, if one shorted out then total Vf will be around 6V.
So if you use 9V without current limiter on the LED string that is shorted out then you can damage the good LEDs in that string because you feeding 9v into 6V string. ALWAYS use constant current source power supply to limit the current to safe level.
Do the experiment to learn.

[vinceroger69]

Re: Seiki 50 inch has no back light

This is one of the ways we currently use and convert some televisions just for fun


https://www.youtube.com/watch?v=X6Frth0F5x0

Thats a good video what i dont understand is how do you control the brightness as in one of the comments its says you can lower it to a black screen

[dick_barton]

Re: Seiki 50 inch has no back light

I don't believe the backlight is adjustable after the modification.

[vinceroger69]

Re: Seiki 50 inch has no back light

I don't believe the backlight is adjustable after the modification.

thats what i thought but in the comments he replies everything is adjustable

EDIT heres what was said

Candido Membrebe1 day ago
nice question sir thariq thahakoya,the led bright was tune to permanent desired brightness but still the screen brightness and colors,were adjustable,tint,color.contrast,sharpness, brightness were all functioning tune all adjustment to zero will produce black screen,there are other lcd tv model that shadow still visible despite zeroing all adjustment,contrary to a 50/50 game,this is a 100 percent job will done simply because we do led tv conversion only to those lcd tv that operate 5 hours to 24 hours with a problem of no picture has sound ,when converting an lcd tv brand with auto power off feature when its own backlight system failed make sure to disable the auto power off feature or refuse to convert the said lcd tv brand to avoid wasting a precious time, remember precious time is on the line when conducting an lcd tv conversion to led tv thank you sir thariq thahakoya for this important question

[electronicsurplus]

Re: Seiki 50 inch has no back light

If one of the LED in the string is shorted out then the circuit can still complete the circuit, the current will just flow through the shorted out device. If the LED goes open circuit then the string will not light up.
I.E. 3V per LED, 3 LEDs in series so total Vf = 9V, if one shorted out then total Vf will be around 6V.
So if you use 9V without current limiter on the LED string that is shorted out then you can damage the good LEDs in that string because you feeding 9v into 6V string. ALWAYS use constant current source power supply to limit the current to safe level.
Do the experiment to learn.

BudM,

So, the device that ShopJimmy sells will not work if an Led is open and, only work if it is shorted?

If so, then the device is not of much use since many times Leds go open correct?

[vinceroger69]

Re: Seiki 50 inch has no back light

maybe worth watching if you have not seen it
https://www.youtube.com/watch?v=4DS8_utsLPo

[CapLeaker]

Re: Seiki 50 inch has no back light

maybe worth watching if you have not seen it
https://www.youtube.com/watch?v=4DS8_utsLPo

Anyone can do that with a proper CV CC variable bench PSU.