Hisense 55K20DG LED Voltage questions

[102mm]

Picked up a Hisense 55K20DG from the dump today. screen is good and it powers up and works with no backlight, i can see the image with a flashlight. so i'll assume that i have bad LEDs somewhere.. my question is what is normal range for the LED voltage? the LED power was between 230 and 248V when i checked it.. and is there a way to check an individual LED strip? there are 11 strips in that panel from what i can see.

Also when i checked the power supply voltages the 16V was running at 19V but the TV was working.. should i be concerned about that too? attached are stock images. If needed, I'll post pictures tonight when i get off.

[budm]

Re: Hisense 55K20DG LED Voltage questions

"the LED power was between 230 and 248V when i checked it"
That Voltage looks to be open circuit Voltage due to no load, so more likely the LED string as open connection, the LEDs are connected in series to form one string.
The filter caps for the LED boosted converter is rated at 250VDC so it is right at the border line, do not run it too long with no load connected.
The Voltage should be less than that when the LEDs are OK, I expect it to be <200VDC.

[102mm]

Re: Hisense 55K20DG LED Voltage questions

Great! thank you.. I plan on tearing down sometime this week.

[cperiuta]

Re: Hisense 55K20DG LED Voltage questions

For same TV, same power supply I got 7 blinks code.

I checked the board and I found burn signs on SFF1506 (see photo). It seems to be OEM parts and I don't find the dataspecs for it.

Can somebody help me to identify this diode please?

Thanks

[budm]

Re: Hisense 55K20DG LED Voltage questions

Are you getting close to 400VDC between the two legs of the main filter cap? That is the PFC Booster Diode.
How do the solder joints look on the two solder pads where the legs are soldered to? It looks like flux to me.
DACO semiconductor, it may not be made any more, not listed on web site:
http://www.dacosemi.com.tw/exec/prod...TO--220AC&lg=E

[cperiuta]

Re: Hisense 55K20DG LED Voltage questions

Thanks budm for your quick answer

mesured 387.9 V for C810 and C811

The solder joints looks good on PFC, but when I opened the tv I found smut on it and it was smelling burn. Also, the legs are black. Do you think I should change it? SFF1006 has the same design, not sure for caracteristics.

The TV gives 7 blinks when it starts and I can see for short time the start logo. Than with a light I can see image on the screen, but I have no sound.

what do you think? thanks

[cperiuta]

Re: Hisense 55K20DG LED Voltage questions

How can check the power supply if it gives right voltage? I my case seems to be T-Com or Main board the problem

Can someone help me with service manual for Insignia NS-55D550NA?

Thanks

[budm]

Re: Hisense 55K20DG LED Voltage questions

Thanks budm for your quick answer

mesured 387.9 V for C810 and C811

The solder joints looks good on PFC, but when I opened the tv I found smut on it and it was smelling burn. Also, the legs are black. Do you think I should change it? SFF1006 has the same design, not sure for caracteristics.

The TV gives 7 blinks when it starts and I can see for short time the start logo. Than with a light I can see image on the screen, but I have no sound.

what do you think? thanks

The PFC Voltage booster is working and the diode is functioning otherwise you will not have that 387VDC on the main filter caps. You can resolder the legs of the diode just in case it has poor connection.
I do not know what the 7-blink codes mean.
Right now we know that you do not have backlights so we need to check the backlights circuit next.

'my question is what is normal range for the LED voltage? the LED power was between 230 and 248V when i checked it.. and is there a way to check an individual LED strip? there are 11 strips in that panel from what i can see.' So you already tear down the screen to get to the LED strips already?

[cperiuta]

Re: Hisense 55K20DG LED Voltage questions

Not yet. I checked both caps C955 and C953 and I found different voltage, one was 235-245V and the other 110.8V. That means there are 2 led strings ans I have no load on the first one? what should I check before I tear down it?

Thanks

[budm]

Re: Hisense 55K20DG LED Voltage questions

One thing I never get to see is the whole back side of the TV so I can see how all the boards are connected together, can you take good pictures and upload it?

[budm]

Re: Hisense 55K20DG LED Voltage questions

The LED strings inside the panel are connected in series to form one big long string.
Have the black probe on the chassis, red probe on the LED connector PIN 1P, turn on the TV and record the Voltage reading and wait for a couple second to see if the Voltage drops down, then do the same again without the LED connector in place.
BTW, you can use RED PROBE the positive leg of C955 instead putting at pin 1P. If you look at the board, pin 1P, 1N, and 2P are all connector together.
I believe what you are going to see is that you will get the same Voltage reading with or without the LED connector in place.

[cperiuta]

Re: Hisense 55K20DG LED Voltage questions

Yes, you're right 1P, 1N and 2P are together. I found 233-245V with/without led connection.

So, one led is not working and I have to check all strips. What about the sound?

I will tear down the screen today.

Thank you budm!

[budm]

Re: Hisense 55K20DG LED Voltage questions

Too bad the OP did not have follow up to show us what he finds inside the panel.

[cperiuta]

Re: Hisense 55K20DG LED Voltage questions

I found at least 4 leds burn. Do you have a recomandation where to buy these leds? Do I have to change all leds or it's not necessary?

Thanks

[cperiuta]

Re: Hisense 55K20DG LED Voltage questions

I have 6 string in good shape and 5 are not ok. The code that is on the string seems to be OEM. I don't find these on sale.

On the label is mention 94V. It think each led should have 3V, 240/77, right? What is 94V stand for?

What is your suggestion at this point?

Thanks

[budm]

Re: Hisense 55K20DG LED Voltage questions

94V: http://web.rtpcompany.com/info/ul/ul94v012.htm
I would try getting new strips, it will not be easy to find.
P/N: SVH550AA2_REV05_7LED

[cperiuta]

Re: Hisense 55K20DG LED Voltage questions

I don't find this...

What do you think about these?
https://www.shopjimmy.com/samsung-de...face-board.htm
https://www.shopjimmy.com/samsung-de...face-board.htm

Thanks

[budm]

Re: Hisense 55K20DG LED Voltage questions

I don't find this...

What do you think about these?
https://www.shopjimmy.com/samsung-de...face-board.htm
https://www.shopjimmy.com/samsung-de...face-board.htm

Thanks

That may work, you just have to do some mod to wire them up the same as original, and when you done, make sure to turn down the backlights level as low as you can but still get good pictures.

[jackfish]

Re: Hisense 55K20DG LED Voltage questions

Same problem...same tv....leds burnt out....think it almozt started a fire...i can see the image with a flaslight...

[jackfish]

Re: Hisense 55K20DG LED Voltage questions

Did you manage to find new leds. ..sold out at two places i looked at...