Samsung Le40C550J1WXXC Backlight

[nezocas]

Hello,

I am strouglling with this TV.
Model: Le40C550J1WXXC and inverter and power suplly BN-4400340B

It boots up normally, but no backligth.
I have check the PFC resistors from 814 to 818 and resolder all of them, I get 380Vdc on the 100uf 450v caps.
I have checked DP803 / ZDM806 / QM801 / ZI802 / QP801 802 / QI801 803
Replaced IPC801 fan7530
All solder joints were checked and also the electrolitics for capacitance and ESR.

I am lost, can someone help me with this issue.

Best regards
Nezocas

[nomoresonys]

Re: Samsung Backligth

Did you do the torch test, shine a flashlight on screen hit menu button, look closely, can you see any text or display?

[nomoresonys]

Re: Samsung Backligth

While its on check voltages of connector CN802, 1-18, report here. like 1 pin b13 and the voltage, 2 pin xxx and so forth.

[nezocas]

Re: Samsung Backligth

Hello,
Image is present, tcon as got the 12v present, image is not so easy to see in this ccfl lcd´s.... its easy to see in led´s sets.
Here goes the voltages:

1- 12.95
2- 0
3- 12.95
4- 4.49
5- 12.95
6- 2.08
7- 0
8- 1.78
9- 0
10- 0
11- 5.25
12- 0
13- 5.25
14- 5.25
15- 12.95
16- 5.26
17- 12.95
18- 2.11

18 PS-on
16 A5v
15/17 B13v
11/13/14 B5v
9/10/12 Gnd
8 H_Sync
6 E-Pwm
4 BL-on
2 5v det
1/3/5 B13v

[nomoresonys]

Re: Samsung Backligth

No pictures, does this tv have separate inverter board/s or no?

[nezocas]

Re: Samsung Backligth

Yes it does

[momaka]

Re: Samsung Backligth

Not sure if this would be of any help, but the same PSU board appears to be used in Samsung LN40c630 sets (at least the one I have does.) That means the inverter board should be similar and/or compatible from those models too, I imagine.

BTW, when you try the TV in a very dark room, does the backlight flash even for a split second when powering on the set. Try it a few times and look carefully.

If I remember correctly, the HV inverter section on the BN44-00340B PSU board has a separate fuse for itself - the one on the right to the big yellow 450V caps. See if that's still OK... but first make sure the TV is unplugged and 450V caps discharged. Otherwise you may damage your meter. If blown, check the two MOSFETs and protection diodes in front of them that drive the inverter transformer. If all of these are OK, the issue might be on the inverter board or with one of the CCFLs.

[nomoresonys]

Re: Samsung Backligth

My memory is gone but there's a way to ohm out those transformers on the inverter board, they need to be pretty close compared to the others if you find a difference among them, it may be bad ccfl or transformer, there's some good videos on you tube, might be hard to find this exact model. Can also check the diodes capacitors and resistors on that board, might get lucky and find one bad.

[nezocas]

Re: Samsung Backligth

Understood.
Fuse is OK
But there is no backligth even for a split second.
And Sansungs should lit up the backligth if the main is disconnected.... not this one.

[nezocas]

Re: Samsung Backligth

My memory is gone but there's a way to ohm out those transformers on the inverter board, they need to be pretty close compared to the others if you find a difference among them, it may be bad ccfl or transformer, there's some good videos on you tube, might be hard to find this exact model. Can also check the diodes capacitors and resistors on that board, might get lucky and find one bad.

Will check them

[nomoresonys]

Re: Samsung Backligth

This may be close for the transformer testing: https://www.youtube.com/watch?v=b36w2GNrH6Y

[nezocas]

Re: Samsung Backligth

Hi,

Just received another Samsung but with same power supply.
Changed it and problem is on the power supply.

I have allready changed from one board to the other ICP801 / UI801 / UI805 and problem still presists in the defective board.

I will change the 2 big inverter transformers.... lets see if it works

[nezocas]

Re: Samsung Le40C550J1WXXC Backlight

No joy with the transformers.

Checked and compared the voltages of both boards and all are the same, even the 380v boost on the caps.

The only diference is the 5v detect that is at 0v at pin2 of the CN802 connector.
On the good board the 5v are present

[momaka]

Re: Samsung Le40C550J1WXXC Backlight

The only diference is the 5v detect that is at 0v at pin2 of the CN802 connector.
On the good board the 5v are present

That could well be the issue.
Good to hear you now have two boards to compare results with.

I'd say follow that 5V Detect line and see what generates it. If it's some IC or complex circuit, I wonder if it can be disconnected and pulled up to 5V from the standby supply via a 100-1000 Ohm resistor and if that would get the inverter running again.

By the way, did this board have a power relay on the PSU input? When you try to power the TV, does this relay keep clicking On and Off? I know I have a 46" Samsung with a different PSU board that does this and still haven't gotten around to find what the issue is. Replacement boards are too expensive so I just chip away at it whenever I feel like it. $30-40 per board for an old 46" LCD TV is ridiculous IMO... and some sellers are asking even higher prices than that. I can get a working TV for the same on local classifieds.

[nezocas]

Re: Samsung Le40C550J1WXXC Backlight

Hello momaka.

No this power supply does not have rellays on it.
Not sure where this 5v should be generated..... I have tried to compare several components by checking both boards but cant find any diferences.

Give me your tv part number and I can check in my database where is your problem.