Samsung 32" power supply BN44-0351B no backlight

[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

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

[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.

[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?

[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

[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

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

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

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.

[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?

[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

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..

[dick_barton]

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

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.

[budm]

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.

[seve91]

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

short done, and TV is working!!! THANKS A LOT!! so maybe is the opto isolator that doesn't switch on the QS801?

[dick_barton]

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

I think the problem is around QS801 and the diodes as indicated by Thoma in an earlier post.
There is 13V at pin 3 of QS801 and when Power On/Off is taken high and the opto-isolator PCS802S/B acting as a switch then shorts the 13V to RS809/RS810 taking the base to 13V. The emitter voltage should then be at the base voltage minus 0.7V.

As a quick test, but at your own risk, I would quickly short QS801 emitter and collector to enable Multi_Vcc and see if the backlights come on.

[seve91]

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

black probe put in the GND pin of each IC measured

[dick_barton]

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

Did you put your black meter lead on power ground to take the readings and not on the chassis?

[seve91]

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

Ok....

ICP801 pin 8 (VCC) = 1.60V
ICP801 pin 1 (FB) = 1.84V
ICM801 pin 3 (VCC) = 1.62V

[dick_barton]

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

In your first post #1, you said you had sound and picture but no backlight so that would indicate that either the led voltage is missing, led driver is faulty or there is an led fault.

ICP801 drives the circuits that give you the secondary voltages A, D12V, Vamp, D5.3 and STBY5.2V and since you said everything but the backlights are working then its not likely that ICP801 is faulty.

You also said earlier that pin 2 (as shown on the schematic) of QD801 was at 0.3V and this supplies the voltage to pin 1 of ICD801. If this is the case then without a supply voltage to that IC, there can be no led boost voltage.

ICM801 pin 3 (VCC) = ??
ICP801 pin 8 (VCC) = ??