sourcing led backlight strips...

[hicksvilleshick]

Seeking suggestions on finding either a replacement for my sanyo dp46142 or a place to get a strip that will work to just light it up and plug in separately.

This tv functions other than the backlight, and while we've found the bad led on the backlight strip, and tried to jump it and those have failed, still just flashes the backlight on startup but it won't stay on...

Thanks.

[MagicSmoke]

Re: sourcing led backlight strips...

Radio Shack has led strips for "project building" I saw them when I got a new tip for my desoldering iron.

I did not look at them closely for specs though.

[CapLeaker]

Re: sourcing led backlight strips...

Seeking suggestions on finding either a replacement for my sanyo dp46142 or a place to get a strip that will work to just light it up and plug in separately.

This tv functions other than the backlight, and while we've found the bad led on the backlight strip, and tried to jump it and those have failed, still just flashes the backlight on startup but it won't stay on...

Thanks.

That's because the LED supply is current controlled. One LED not working changes the current consumption. So if one is out, even if you bridge it, the supply is shutting down, the correct current hasn't been drawn. However... you can find these LED's for cheap on these Chinese websites like aliexpress, dx, etc.

[electronicsurplus]

Re: sourcing led backlight strips...

In other words, each Led requires approx 3.2 Volts each to light. So, if you have 20 Leds on a strip this would require 64 Volts, If you bridge or jump one or more of the Leds, the voltage to each Led also changes, which will result in the MainBoard to Signal Shutdown the Power Supply (When there is too much draw or, not enough draw) and, in some cases will burn out more Leds due to excessive voltage. This is a safety feature which was added by Law or Rule due to overwhelming amount of Home Fires as the direct result of Televisions. Therefore, they will go into Safety Shutdown.

There are some methods to 'temporarily' override this circuit depending on type and model television and, force the TV on.

Just wanted to add a helpful note

Aimee

[lookimback]

Re: sourcing led backlight strips...

Wouldn't it be possible to jump it with a resistor which had the same resistance as the bad LED?

[budm]

Re: sourcing led backlight strips...

You can use 3.3V Zener 1n4728 1W (1n5333 is 5W) in place to test if that will make it stays on, the Zener will be connected in the reverse polarity of the LED.

[johnboy1313]

Re: sourcing led backlight strips...

I have a ton of salvaged LED strips. How many LEDs do you need on the strip? I think I have some with six LEDs and some with eight. You would likely have to make a connector, but it's not impossible.

[lookimback]

Re: sourcing led backlight strips...

Or pull an LED and use it on his strip.

[saddle_au]

Re: sourcing led backlight strips...

More than likely, there will be something else wrong on the driver board for the leds.

Most of these strips that I have pulled out, connect to a board that controls the current going in, not the voltage across the strip. Very simple drivers in cheaper models may just apply a voltage and look at the voltage drop of across a resistor in series with the strip. Almost all of them run some type of pwm signal to the leds that is synced to the tcon or ldvs output to stop stroboscopic (wagon wheel) effects.

I have shorted a bad led on some in the (recent) past to check functionality, then replaced it from spares. If you have a strip of 8 and reduce it to 7, the voltage change for the driver is not that much greater than the difference between 7 leds going from hot to cold (they change voltage drop with temp) when driven hard.

If you still cannot make it go and don't have any suitable leds as spares, make a small string of 5 normal 1 amp diodes (1n4XXX) wired in series across the offending led (be careful about not shorting to the metal chassis). Wiring the diodes as a block can be done in a very small space, as shown in the attached picture. If that works and you don't think the missing led is so obvious on the panel, paint the diodes white and leave them there.

Alternatively, remove a good led from the end of a chain (near the edge of the screen) and put it in the offenders location, then put the leds where it came from.

[lookimback]

Re: sourcing led backlight strips...

Another option is to search ebay for the model number of the TV and then follow the search. Then, you will get an alert when new items are listed and, if you then immediately contact the seller who just listed items and inquire about the LEDs, he may actually have them but didn't think they were worth listing. I have actually done this when I needed parts which sellers never waste their time on and it does sometimes work.

[hicksvilleshick]

Re: sourcing led backlight strips...

First off, thank you all for your responses. So much info here that cleared up many things for me.

Ok I want to say there are more than 16 leds, I've tried looking for them on ebay with no success for my model, that would be ideal honestly, but I just want the damn thing to work. I've got 2 driver boards and it acts the same with both (just flicker of backlight at startup)

aliexpress is something I'll have to check out and see if it's something I can swing... I've been able to identify it's a samsung panel and all that but haven't had luck finding a source. I could find the whole panel a couple of places, but not just the backlight piece.

and I'll have to check radio shack too and see what I could do, may do that as a for now. as good as I'm getting at pulling this thing apart and putting it back together... lol

again many thanks!

[lookimback]

Re: sourcing led backlight strips...

You got a part number for the LED strips?

[hicksvilleshick]

Re: sourcing led backlight strips...

You got a part number for the LED strips?

No. I gotta pull it back apart and see if it's labeled. I know it's a samsung panel LTA460HN05-T02

but my searches for that have been fruitless.

[lookimback]

Re: sourcing led backlight strips...

OK, because I know I have some strips. I just don't remember what they go to. Are they the edge lit type or the ones which are on the back?

[hicksvilleshick]

Re: sourcing led backlight strips...

OK, because I know I have some strips. I just don't remember what they go to. Are they the edge lit type or the ones which are on the back?

Edge... it's kinda odd, only on left side of panel, and under a metal plate... it seems they are just glued to the metal cover.

here's a not so great pic.



I don't think that shows quite the full length, but close. (I just found this pic, I'm sure it would've been helpful earlier.)

[lookimback]

Re: sourcing led backlight strips...

Those are edge lit then. I have to look in my basement and see if I have any I haven't pulled yet. When you open it up, get some closeups of the individual LEDs. I've got a couple different types, but probably not that same strip. If they're the same, I can pull a few and send them to you.

[lookimback]

Re: sourcing led backlight strips...

I found one more type in the basement. Here's a pic of the 3 types I have. 2 strips say 94v so I suppose I can divide that by the number of LEDs to get individual voltage ratings. Third strip doesn't say.

[hicksvilleshick]

Re: sourcing led backlight strips...

I found one more type in the basement. Here's a pic of the 3 types I have. 2 strips say 94v so I suppose I can divide that by the number of LEDs to get individual voltage ratings. Third strip doesn't say.

They are identical to the ones on the bottom...

Here's a close up...



iirc, I was told they are 3.2v but I'm pretty clueless when you get that far into it.

Here's a link to my first thread hunting this down... if it's helpful.
https://www.badcaps.net/forum/showthread.php?t=40892

[lookimback]

Re: sourcing led backlight strips...

They're approximately 3mm by 5mm, not counting contacts.

[hicksvilleshick]

Re: sourcing led backlight strips...

They're approximately 3mm by 5mm, not counting contacts.

I'm lost there, I couldn't tell you how long/wide they are, but they appear to be the same type as that bottom set you posted. Are there different sizes of that type?

I will pull it apart either tonight or tomorrow morning and see if I can get a measurement on them...