Samsung 32" power supply BN44-0351B no backlight

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

tomorrow i will check and i will let you know, thanks.
I notice also a black spot on the top of the screen...looks like a burner LED backlight..

[budm]

Re: Samsung 32" power supply BN44-0351B no backlight

I will not run the TV until more verification.

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

So what is the PFC Voltage now?
ICS802 is part of the PFC Over Voltage protection that will not allow QS801 from coming on by bypassing the bias current for QS801 to GND.

As Budm has requested, what is the PFC voltage when the set is forced on by shorting emitter/collector?

You need to check QS801. Youtube have plenty of video's that show you how to test it with your meter. The opto-isolator is fine and does not need to be replaced. It shorts the collector voltage to the base of QS801 when the Power ON/OFF input is taken high as it should.

I would also replace the zener diode ZDS806 and diode DS806 connected to the base of QS801 as suggested by Thoma then your tv will be repaired properly.

PFC-OUT is now 380V. To test QS801 is better to desolder it, isn't it?

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

desoldered QS801 and tested using multimeter in diode mode...it's ok.
Tested also DS806 without desoldering, and it's good.
Desoldered and tested ZDS806 using multimeter in diode mode...OK.

[dick_barton]

Re: Samsung 32" power supply BN44-0351B no backlight

Replace QS801. I'm pretty certain it's faulty.

There's a supply into the collector and the opto-isolator is switched on and puts the voltage on the base.
DS806 & ZDS806 I suspect are fine. When the voltage into ICS802 reaches 2.5V or greater it starts to block the voltage to the emitter of QS801 by reducing the voltage on the base. That's not the problem because the voltage is there so I don't believe ICS802 is at fault or the voltage being fed to ICS802 from R840, 841, 842, 843, 846, 847, 844 is greater than 2.5V so the PFC circuit is not over voltage.

From the photo's above you also appear to have at least one faulty led that needs to be replaced.

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

how do you say it's faulty? I tested only in diode mode...i usually test B-C and B-E, then i reverse the probes...first time OL, second time 0.6, so i supposed was fine.

What about faulty led? is it possible to replace only one led? i have to find the right model disassembling the tv

[dick_barton]

Re: Samsung 32" power supply BN44-0351B no backlight

Only a suggestion since I cannot think of what else it could be.

There are plenty of Youtube video's showing you how to replace the leds.

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

ok i will try to find the same model of BJT and replace it.
If it will solve the issue, then i have to learn a new method to test the transistors

[budm]

Re: Samsung 32" power supply BN44-0351B no backlight

Right now what dcv (in circuit when TV is turned on) do you have between E and B of that Transistor?

[R_J]

Re: Samsung 32" power supply BN44-0351B no backlight

Why not try shorting PCS802S/B (e-c) if the QS801, etc. are ok the tv should turn on.
Or try shorting QS871 e-c to see if the tv comes on
Power on/off controls QS871, If QS871 is turned on it connects PCS802S/A to ground causing its led (in the optocoupler) to light.

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

i'll try and let you know...i've disassembled the panel, and the TV got two stripes of LED named LMB-3200BM11. Can't find the replacement....i am able to desolder and resolder and smd led, but i need the exact model of that led

[dick_barton]

Re: Samsung 32" power supply BN44-0351B no backlight

Have a look at:-

http://www.ebay.it/itm/152536779696

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

Right now what dcv (in circuit when TV is turned on) do you have between E and B of that Transistor?

with C-E shorted, is 0.15V

Have a look at:-

http://www.ebay.it/itm/152536779696

expired

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

[Moreno83]

Re: Samsung 32" power supply BN44-0351B no backlight

That is a burned LED!

Looks like a Osram Duris E5 LED....

https://www.led-tech.de/en/High-Powe...0_206_216.html

replace the faulty led.

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

That is a burned LED!

Looks like a Osram Duris E5 LED....

https://www.led-tech.de/en/High-Powe...0_206_216.html

replace the faulty led.

thanks looks like very similar...but which temperature? 2700k? 3000k? 5700k?

and...how many? i suppose that they are connected in parallel, so it's not only one burned.

[Moreno83]

Re: Samsung 32" power supply BN44-0351B no backlight

They are connected in series. If 1 dies , the whole strip is off. ( Christmas lights ).

So in this case it looks like you only need one. Not sure about the lumen , maybe someone else can answer that. Maybe it is in the service manual.....

[Moreno83]

Re: Samsung 32" power supply BN44-0351B no backlight

The best thing you can do is google the led strip name!

https://www.vareza-elektronik.de/pro...85&language=en

[dskall]

Re: Samsung 32" power supply BN44-0351B no backlight

Bright white which has a bluish tint. So I would say 5700K. Others will give yellowish tint

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

thanks...i've ordered 10 of them, plus a 15V zener because i've lost the small one i've desoldered for testing