How to troubleshoot a BN44-00424A

[Vista20]

I have a Samsung UN55D6050TFXZA Ver. H301. While watching this TV it just turned off. I tried to turn it back on but nothing at all, no picture and no sound. The only thing I saw was the red LED at the bottom right blinking periodically.

I'm a low voltage contractor and have repaired few electronics in my day, replaced caps in a monitor, re-soldered some cold/cracked solder connections in an old tube TV, all with very good success. Usually, I replace modules rather than repair them.

I scoured lots of websites, including this one and have tried to isolate the problem which I think is the power supply or backlight LEDs. I tried to eliminate the backlighting LEDs by disconnecting the main board from the power supply. I could not see any light through the holes in the back of the panel. I looked at both sides of the power supply and see no damage, no burned areas, and no apparent bad caps. I checked the two PS onboard fuses with a continuity checker and they seem fine.

I'd like to test the power supply with my meter to see if it is outputting voltage to the LED strips. But, is this possible with the main board unplugged? Doesn't the main board switch on the power to the LED strips?
Is there a write up on how to troubleshoot this particular power supply or one similar to it? I see the ratings and pin outs next to the LED connector on the PS. Is there a common issue with this particular make and model TV?

Thanks.

[budm]

Re: How to troubleshoot a BN44-00424A

You can start by upload good clear pictures of YOUR boards and how they are connected together, the the DC Voltage readings of all the pins of the connector of the power supply board that goes to the main board with and without the connector in place, and when TV is in STBY and when TV is turned on.

[Vista20]

Re: How to troubleshoot a BN44-00424A

Using my meter, I was unable to record any voltages from the pin header CNM803 in either standby or on, main board connected and disconnected. My meter auto selects ac/dc voltages. I used pin 11 for GND, and I confirmed GND continuity of pin 11 with the chassis.

One thing that leads me to believe the power supply has a problem is the lighting in the room slightly flickered when I plugged in the TV electrical cord to the wall receptacle.

I see the red LED on the bottom right of the bezel blinking periodically. Is there a pattern that I should watch for?

I'm attaching some photos below:

[aaronwt6]

Re: How to troubleshoot a BN44-00424A

Unplug the connector between the main board and the power supply. Then connect the power cord and see if the backlights come on. If they do, then it's almost certainly a main board issue.

[Vista20]

Re: How to troubleshoot a BN44-00424A

I did that a few nights ago, just tried it again, and no lights.

[Vista20]

Re: How to troubleshoot a BN44-00424A

Update:
I rechecked my power supply pin out header with the main board connected. I was not reading the voltages correctly but now I think I have it.

On Pin 3 and Pin 5, I'm getting 12.70 Volts for a second and then it reduces to 0-1 volts, as if it's cycling on / off.

On Pin 13 and Pin 15, I'm getting 5.32 Volts for a second and then it reduces to 0-1 volts, also appears to be cycling on / off.

When I disconnect the main board from the power supply, the voltages seem to reduce to 0-1 and doesn't show anything higher.

So, now I wondering if this is a main board problem, rather than a power supply.

[budm]

Re: How to troubleshoot a BN44-00424A

We need pin name and follow by the Voltage reading (in standby and when power switch is activated)so we can easily see what are there what are not there at those pins.

[Vista20]

Re: How to troubleshoot a BN44-00424A

budm, thanks for replying. I'm having trouble determining when the TV is in standby and when the power switch is on because the only thing that happens when I use the remote or press the I/O button on the TV is the Standby LED blinks rapidly for a second. This TV has controls on the bezel, but they're merely labels not actual buttons. I assume that they work via touch capacitance or slight pressure on the label.

I'll make a legend of the pins with their respective voltages. However, it will only be a guess whether the voltages are in standby or with power on.

[budm]

Re: How to troubleshoot a BN44-00424A

Just take the readings when the TV is first plugged in, then after using the remote to turn on the TV.

[Vista20]

Re: How to troubleshoot a BN44-00424A

Well, I tried it 3 times, unplugged the power cord, waited, restored power and read voltages. No changes from the voltages recorded after I actuated the remote and the I/O control. It's as if it's locked in one mode and I can't change it.

All the voltages recorded are not steady. The rated output voltage appears, then drops, then reappears at the rated voltage. Recycling.

[Vista20]

Re: How to troubleshoot a BN44-00424A

Here is the pin out from the power supply board.

[Vista20]

Re: How to troubleshoot a BN44-00424A

I see that the kit I purchased from ShopJimmy contains MOSFETS, some fuses, a resistor, a film capacitor, and a few other IC components. There doesn't seem to be an on circuit test for the MOSFETS, and from what I've seen on Youtube, these will not show any exterior signs of a problem. It looks like I'll need to take them off the board to test them, and I'll replace them with new ones. The kit has two identical N-channel MOSFETs, however, when I test them one give a much different value than the other. Are value readings critical with these? One reads .682 VDC the other 1.227 VDC.

The MOSFETs are secured to the underside of the heat sinks and I've bought replacement thermal paste. I see some of the components are secured with a silicone compound. I've researched this and learned that non-corrosive silicone is the thing to use. Is there such a product that I can find at a local store? Or is this something I must order from a place like Digikey? It looks like the heat sink must come off the board for the replacement of the MOSFETs.

[Andrew F. Ali]

Re: How to troubleshoot a BN44-00424A

What is the Model no. of the TV this PSU is for? Since you asked, follow precisely the advice and instructions given. You seem not to be following. Probably because you don't fully understand. It's simple:
1. Reconnect all the boards as they were.
2. Plug in TV to the ac and using the chassis as GND, set DMM to 20Vdc.
3. Connect the BLACK probe to GND.
4. With the RED probe, measure the on CNM 803 pin14-A5V, if 5Vdc is present.
5. If present, turn on the TV. Measure on CNM 803 pin16-PS-ON, if >2.0Vdc is present and constant.
6. If present and constant. Measure on CNM 803 pin18-BLU-ON if >2.0Vdc is present and constant.
7. On CNM 803 pin3&5-B13V, if 13Vdc is present, Backlight should be ON.
8. On CNM 803 pin13&15-B5V.

[Vista20]

Re: How to troubleshoot a BN44-00424A

Andrew, thanks for replying. I've tried everything that you mentioned several times and wind up with the same results.

This is a Samsung UN55D6050TFXZA Ver. H301, PSU BN44-00424A.

1. All boards are connected.
2. My Fluke 117 auto senses the DC and auto adjusts.
3. Black probe is connected to chassis GND.
4. After unplugging the AC for several hours I plugged in the AC and measured CNM 803 pin 14/13, 5.35VDC is present but not constant. It's present for 2 seconds then drops to 0, then back up to 5.35VDC for 2 seconds, then drops again, over and over.
5. Turning on the TV is a problem as I can't tell when it's ON. The STBY light blinks no matter what I do with the remote or the I/O on the bezel. All rated voltages are present at the respective pins, but they're not constant. They cycle at 2 second intervals. Rated voltage for 2 seconds, then to 0, then repeats.

[Andrew F. Ali]

Re: How to troubleshoot a BN44-00424A

Then that could be a problem with the PFC circuit. Std-by 5V source circuit. If the PSU is good with the Main Bd disconnected from the PSU and the Backlights connected, plug in the TV to the ac....the backlights should come on right away and stay on.

[Vista20]

Re: How to troubleshoot a BN44-00424A

Andrew, I disconnected the main board from the PSU but do not see any back lights through the holes in the chassis. I read the voltages again and found the B5V shows 5.35VDC is still present but not constant. All the other voltages 12V and 18V pins were still present but were now reduced by 1-2 volts and were not constant either. They are still cycling on and off.

The PFC, which I researched, stands for Power Factor Correction, is that right? And, if so, what part of the board and what component should I be looking at? Once I find it, or them, is there a DMM test?

[Vista20]

Re: How to troubleshoot a BN44-00424A

I bought an LED TV Backlight Tester GJ2C and, with the TV assembled and the LEDs unplugged from the PSU, I checked the backlight. The LEDs lit up and could be seen through the holes in the chassis.

So, does this rule out a problem with the LED backlighting? Is there any reason to disassemble the TV and check LED strips individually?

Or, is the focus back onto the PSU for my problem. Andrew mentioned that the problem might be the PFC. With the parts in the BN44-00424A repair kit, which I purchased from ShopJimmy.com, would these address the PFC? I see there are a few MOSFETs, a film capacitor, a resistor, a few fuses and a few IC components.

[Vista20]

Tested LED back lights w/o disassembly. Results?

As mentioned earlier, I used a LED TV Backlight Tester, GJ2C, without disassembling my TV. I see the lights through the many holes in the chassis.

1. Does this mean they're all functioning?

2. Could some of them be out while the others are not, allowing some light to show through the chassis?

3. Are the individual LEDS wired in parallel on each strip? Or, are they wired in series? I assume if they are wired in series, I would see no light at all.

4. Is this a reliable test, to rule out an LED backlight problem? Or do I still need to disassemble and test each LED individually?

[budm]

Re: How to troubleshoot a BN44-00424A

Your Voltage readings per your PDF are not right at all.
You need to retest and count the pin corectly, as you can see, you show 18.9V on the GND pin!, EPWM of 12V! BL-ON of 18.9V!
We need the correct DATA first.

[Vista20]

Re: How to troubleshoot a BN44-00424A

Budm,
Thanks for sticking with me on this.
Actually, I read those voltages several times to make sure I was on the proper pin and double checked the reading on my meter. The photo I posted earlier shows a legend on the pcb, with the rated voltages per pin. I transferred that legend into post, exactly the way it appears on my psu pcb. So, maybe I'm not fully understanding the data printed on the board.

The GND pin 10 /9 has "Vamp" in the 4th column to the right on the pcb. I thought the legend printed on the pcb titled "Output Rating" defines the markings on CNM803. For example, Vamp (18V), doesn't that mean I should be reading ~18V on the pin marked Vamp?. Also, the others are marked with their respect voltages in the legend on the pcb.

Also, on the board I see two columns of pins:
2/1
4/3
6/5
8/7
10/9
12/11
14/13
16/15

My particular PSU only has the pins on the right column, there are no pins corresponding to the left column on my PSU.