Seiki 50 inch has no back light

[dick_barton]

Re: Seiki 50 inch has no back light

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

I believe that what he means here is that the constant current module was selected to match the led brightness needed. All other screen functions were still available to the user except backlight.

[dick_barton]

Re: Seiki 50 inch has no back light

There also appeared to be one hell of a lot of leds, 20 plus rows and maybe 50/60 leds per row. The leds didn't have any diffusers on them so I suspect that with that number of leds the drive current was probably set low and so as not produce any bright spots when viewing. Just my thoughts,

[vinceroger69]

Re: Seiki 50 inch has no back light

yes that makes sence it did not look a bad picture as the leds didnt have diffusers lens fitted over them.

Edit was typing same time as you same thoughts too regaring the ammount of leds used but if its a good picture and the set lasts a while i suppose thats all what matters if for own use and not re sale.

[electronicsurplus]

Re: Seiki 50 inch has no back light

What I am trying to accomplish is being able to light the Led Back-lights when there exist a bad strip lighting the remaining strips without opening the screen and risking cracking the screen

In other words some way of using resistors and/or diodes in place of the defective Led strip or, to complete the circuit which will allow the remaining strips to light or,

To override or disable/change the protect circuit so the back-lights will light


Any help would be greatly appreciated

[vinceroger69]

Re: Seiki 50 inch has no back light

but when doing that wont you have dark areas on the screen?

[dick_barton]

Re: Seiki 50 inch has no back light

It's a pity the manufactures do not enclose the panel in the same frame as the diffusers so the whole assembly could be lifted off leaving just the leds exposed which would make servicing so much easier.

[electronicsurplus]

Re: Seiki 50 inch has no back light

but when doing that wont you have dark areas on the screen?

Since there are so many Leds I have not noticed a great deal of difference mostly due to the diffusers over the Leds and the white Diffuser panel below the screen tends to spread the light somewhat normal

There is sometimes a barely noticable dim area but, otherwise usable

[electronicsurplus]

Re: Seiki 50 inch has no back light

It's a pity the manufactures do not enclose the panel in the same frame as the diffusers so the whole assembly could be lifted off leaving just the leds exposed which would make servicing so much easier.

That would be way too easy

I think they simply do not want the TVs serviced anymore and simply disposed of
They could care less about our Landfills. Have anyone ever seen theirs? Because, there is not much which can be done with disposed TVs at all without a great deal of effort which always results in backwards investments

In fact, some manufacturers actually use adhesive sealant around the screen frame which requires force to remove and most times results in cracking the screen. Also, the Ribbons are only glued onto the address buffer and many times become unglued which results in lines and bars on the screen

[electronicsurplus]

Re: Seiki 50 inch has no back light

I will try to understand BudM's suggestion IF I can try understanding how to find the test points



See:

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://www.maximintegrated.com/en/a...ex.mvp/id/4384

[budm]

Re: Seiki 50 inch has no back light

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?

Well I think you need to use simple logic, the tool will tell you you have open circuit, just thing about it, if you use Ohm meter to check the resistance of 1 Ohms resistor but it shows open circuit, does that make Ohm meter useless?

[budm]

Re: Seiki 50 inch has no back light

I will try to understand BudM's suggestion IF I can try understanding how to find the test points



See:

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://www.maximintegrated.com/en/a...ex.mvp/id/4384

You have to have knowledge and ability and understanding how to figure out how the LED strips are terminated and how to tell how many LED driver circuits are being used on the LED driver board. That is the starting point. You know how to read circuit diagram, right/ Go to Tom66 web site and down load some of the SAMSUNG service manual and BN44- XXXXX diagram for the power supply and study them.
What is your level of electronics knowledge?
I ask becuause you ask the question in post 38:

"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?"
If you really think about it and use simple logic then you will know why the tool is good, so lets say that the LED string does not light up, then ask yourself, is it because the LED string had open LED or the LED power supply is not working?
If you think the tool is not much use, then think about your meters you use to take measurement, that will make them useless too. The tools tell you what the DUT condition is.

[electronicsurplus]

Re: Seiki 50 inch has no back light

You have to have knowledge and ability and understanding how to figure out how the LED strips are terminated and how to tell how many LED driver circuits are being used on the LED driver board. That is the starting point. You know how to read circuit diagram, right/ Go to Tom66 web site and down load some of the SAMSUNG service manual and BN44- XXXXX diagram for the power supply and study them.
What is your level of electronics knowledge?
I ask becuause you ask the question in post 38:

"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?"
If you really think about it and use simple logic then you will know why the tool is good, so lets say that the LED string does not light up, then ask yourself, is it because the LED string had open LED or the LED power supply is not working?
If you think the tool is not much use, then think about your meters you use to take measurement, that will make them useless too. The tools tell you what the DUT condition is.

That is correct. I understand

I was just under the impression that although the entire string is serial that the Strip was not

Also, I have determined that if I reduce the voltage considering the missing strip or, part of strip that I can make it work

In other words, the entire Strip needs 120 volts to light, which contains 40 Leds and 10 were missing I could then use 90 Volts which should light the backlights if the defective string were jumpered or,

Would it make more sense to use a string of diodes in place and keep the voltage the same? Although the Diodes may generate some heat.

What are your thoughts BudM ?

Thank you in advance

[budm]

Re: Seiki 50 inch has no back light

Reducing the output Voltage of the existing Boost converter power supply can be done if the circuit used in your board matched the application notes of the LED driver IC.
30 LEDs you will need 90V for the total Vf of the LED STRING + V drops (typ. 15~30V) on the PWM Controlled POWER MOSFET and I -sense resistor for maintaining constant current through the LEDs, the key is to maintain constant current through the LED (Vf of LED also change with temperature and the amount of forward bias current, see LED spec sheet for more details).
Bottom line is you can modify the circuit if you have the diagram and the data sheet of the ICs.

[electronicsurplus]

Re: Seiki 50 inch has no back light

I have to say

BudM you are the best!!