Samsung UN40D6400UFXZA Power Cycles

[Ltank]

Re: Samsung UN40D6400UFXZA Power Cycles

I have worked on one of these before. The A side voltages were good and the B side would cycle. It was P.S cyling due to a bad LED backlighting strip. Opened set and jumpered out 4 LED one on each of the 4 channels on the Right side bank. The P.S. senses the open circuit and shuts down but keeps trying to restart. I jumperd the LEDs and the set had a few dim spots but worked.

[budm]

Re: Samsung UN40D6400UFXZA Power Cycles

You can use 100W 120V lamp as the load due to fact that the cold resistance will be about 9 Ohms or so, just measure the resistance of the bulb.

[freakaftr8]

Re: Samsung UN40D6400UFXZA Power Cycles

Actually in the process of working on one of these also model number UN40ES6100. This one will flicker the backlights when you tap on the back. Power supply soldering looks ok. When the backlight is not working one side output voltage goes to around 32v when working goes uo to around 75v. Power supply still supplies mainboard cause I can see an image. even though the power supply is different than your design slightly yours maybe doing a shutdown condition from a shorted led where mine stays on but it seems that these certain TVs are plagued with LED failures of some type or another you may have a shorted strip did you try probing the ground against the positive leads on the LED outputs to see if its grounding out?

this is done by having the LED connector disconnected and probing at the connector with the TV unplug

[twilliard]

Re: Samsung UN40D6400UFXZA Power Cycles

probing the ground against the positive leads on the LED outputs to see if its grounding out Did not show any shorts

[polaris37]

Re: Samsung UN40D6400UFXZA Power Cycles

Did you ever figure out the problem? I just came across the same issue.

[crdz66]

Re: Samsung UN40D6400UFXZA Power Cycles

Just disconnect the wifi or network.
That work for me.

[Malachi]

Re: Samsung UN40D6400UFXZA Power Cycles

I also have this TV with the same problem. It seems the LEDs light up. The whole screen is illuminated and light shines through all the screw openings in the back.
Disconnecting the main board stops the power cycling but then it doesn't nothing.

[Malachi]

Re: Samsung UN40D6400UFXZA Power Cycles

Bump

[budm]

Re: Samsung UN40D6400UFXZA Power Cycles

So let me get this correctly, when the cable between the power supply board and the main board is disconnected then you will have backlights? If that is the case then the power supply and the LED drivers are OK then we can start looking at the main board next.

[Malachi]

Re: Samsung UN40D6400UFXZA Power Cycles

When I disconnect the the main cable from the power supply to the main board I don't get anything.
With everything hooked up it power cycles. The back lighting turns on and off and the smart logo flashes on the screen.

[budm]

Re: Samsung UN40D6400UFXZA Power Cycles

Is your power supply board P/N BN44-00427B just like OP in post #1?

[Malachi]

Re: Samsung UN40D6400UFXZA Power Cycles

Yes, it is.
I get the same readings as twilliard also.
Except I haven't tested it while it's power cycling because I have to put the connector back on and I can't get to the pins.

[budm]

Re: Samsung UN40D6400UFXZA Power Cycles

Just to be sure, So without cable connected, what do you have on pin 20 PS pin?

BTW, same reading as in post #11?

PIN__ LABEL__ My reading
1__ OD_LE__ 2.68
3__ OD_ON__3.16
5__ GND__ 0
7__ B13V__ 12.77
9__ B13V__ 12.77
11__ Vamp__ 12.77
13__ Vamp__ 12.77
15__ GND__ 0
17__ B5V__ 5.33
19__ B5V__ 5.33

PIN__ LABEL__ My reading
2__ PWM4__ 0
4__ PWM3__0
6__ PWM2__ 0
8__ PWM1__ 0
10__ B13V__ 12.77
12__ BLU__ 2.89
14__ GND__ 0
16__ GND__ 0
18__ A5V__ 5.33
20__ PS__ 4.11

[Malachi]

Re: Samsung UN40D6400UFXZA Power Cycles

Pin 20 ps 4.13
I said they were the same but some were like .01 or so different.
Is that not accurate enough? Sorry I'm still new at this.

[budm]

Re: Samsung UN40D6400UFXZA Power Cycles

4.13 VDC is fine, command signal with >2.5VDC is consider as good signal.
So with the board disconnected you do have the Followings:
20__ PS__ 4.11 (4.13 is fine) for power supply ON.
12__ BLU__2.89 (or >2.5VDC) Backlights ON.
But none of the FOUR PWM? We need this Voltage for the backlights to be ON.
These two below I am not sure what they are yet.
1__ OD_LE__ 2.68
3__ OD_ON__3.16

I need to do more digging.

[Malachi]

Re: Samsung UN40D6400UFXZA Power Cycles

But my back lights flash as the TV power cycles. You can see the light through every screw holes in the back from where the screws were taken out.

[budm]

Re: Samsung UN40D6400UFXZA Power Cycles

But it should stay on (as long as the board has 120VAC feeding the board) when you run the power supply-backlights driver board by itself. The board has pull-up resistors to force power supply and backlight circuit so you can do self test without the needs for the main board, that is how newer SAMSUNG power supply boards are setup to do so the tech in the field can easily narrow down as to which board is the problem, in an older board you have to add external resistors to force the board on. I am not 100% sure for the LED 'D' series.
That is why I am not so sure if it goes into safety shutdown due to error or not since I do not know what these two signals are:
1__ OD_LE__ 2.68
3__ OD_ON__3.16

[Malachi]

Re: Samsung UN40D6400UFXZA Power Cycles

Ok. I'm trying to locate a main board.

[budm]

Re: Samsung UN40D6400UFXZA Power Cycles

Can I see the pictures of the whole back side of the TV so I can see how all the boards are connected?

[Malachi]

Re: Samsung UN40D6400UFXZA Power Cycles

Sorry about the quality.