Samsung UN55KU6300FXZA

[iliketofixstuff]

Hi, I've got a Samsung UN55KU6300FXZA that doesn't turn on but does show a blinking red (standby) light. When I press the power button the remote the red light blinks rapidly but faintly, pretty much the entire time I hold down the button.

Before I pay for a new power supply board I am hoping someone else can confirm my determination. Or maybe provide me other things to check before pulling the trigger on a replacement.

I haven't found schematics for the board that I have but I've read up what I can on diagnosing and repairing and have the following information:

Configuration:
Model Number:UN55KU6300FXZA
Version: CJ05
Power Supply board: BN44-00807A
Processor board: BN94-10838D

I have the following tests / results. All measurements are DC volts. I added a #2 and a #3 on top of the board pic to show where I made the measurements (with respect to the chassis ground.)

1. Disconnect power supply board and Turn on TV: No backlight

2. Measure CNL802 (backlight connector) pin 1 indicator: 180V with processor board connected, 88 to 95V with processor board disconnected. If I unplug the backlight connector its about the same - 88 to 100V. If I understand the silkscreen note it seems like this should be either 277 (2D) or 337(3D).

3. Test point at DM853C and DM854C Cathode: 12.8 with periodic drop to ~3V, probably once a second. Also seems to be accompanied by very faint 'pop' or 'tick.' Silkscreen on board says Standby 8V / On 13V. It's definitely not either of those steady state. If I disconnect the processor board, it varies from 9V to 13V.

Anyone have any thoughts they are willing to share? Or additional recommended tests to clarify the problem?

Again, I'm trying to decide if this is enough information to determine that the power supply board is faulty and that replacing it will fix the problem. I can also post pictures of the system layout and harnesses.

Thanks in advance.

[CapLeaker]

Re: Samsung UN55KU6300FXZA

Sounds like the main board isn't returning PSon and BLon to the PSU. So check that first. If you disconnect the PSU, well there won't be anything powering up. If you do make measurements on the hot side (mains) of the PSU, the GND reference is the negative leg of the main filter capacitor. Measurements taken on the secondary, the GND reference is chassis GND. The backlight has a pullup resistor, so if you disconnect the main board from the PSU, and plug the TV in, the backlights should turn on.

[nomoresonys]

Re: Samsung UN55KU6300FXZA

Test connector from mainboard to powerboard on powerboard side with all boards hooked up, test with tv plugged in but off then hit power, report both conditions here, give pin number, pin description/name and condition both off and when you hit power on. So we can see all the voltages and what they are doing. Try to do test just as instructed, example in second link below if needed.

[iliketofixstuff]

Re: Samsung UN55KU6300FXZA

Thanks for the help so far. Here are updated test results.

Configuration: Entire system assembled, plugged in.

'Reading on' is after pressing 'on' button. I noticed no difference. My wife watched the indicator LED on the IR receiver and it blipped the same way as before each time.

Most of these oscillated - both before and after pressing the power button. I estimate they cycled every 2 seconds. Did not time with a stopwatch or scope.

Pin / Signal / Reading Off / Reading On / Note/Comment
1 / FAIL COUNT / 0.3-0.4 / 0.3-0.4
2 / ANA DIM / 0-1.6 / 0-1.6 / period approx 2s
3 / A13V / 12.8 - 3 / 12.8 - 3 / Stable at 12.8, then dropping to 3. period approx 2s
4 / OD ON/OFF / 3.6 - 0 / 3.6 - 0 / period approx 2s
5 / A13V / 12.8 - 3 / 12.8 - 3 / Stable at 12.8, then dropping to 3. period approx 2s
6 / PWM BLU / 0-1.12 / 0-1.12 / period approx 2s
7 / A13V / 12.8 - 3 / 12.8 - 3 / Stable at 12.8, then dropping to 3. period approx 2s
8 / POWER ON / 0-3.4 / 0-3.4 / period approx 2s
9 / A13V / 12.8 - 3 / 12.8 - 3 / Stable at 12.8, then dropping to 3. period approx 2s
10 / GND / not measured / not measured
11 / GND / not measured / not measured
12 / GND
All measurements made with respect to pin 12 (GND) as shown in top of board silk screen. I measured these on the back side of the board using the pinout that I have marked up and attached.

I should have put this in the initial post but forgot: This TV was working fine and just turned off while my daughter was watching it. I don't really think it changes the diagnostic process, just thought it was worth mentioning.

Which is unfortunate because when I was a kid I always told my parents I hadn't done anything when something broke. In almost every case, I had but didn't want to admit it. Seriously though, I have no reason to suspect she did anything. She turns into a zombie when it's on anyway and won't get off the couch for anything.

Also no visual signs of damage on the boards when inspected.

[budm]

Re: Samsung UN55KU6300FXZA

Please repeat the same test again on the power supply but without having the cable connected to the Main board, also test the DC V between the two legs of the main filter cap CP806, report the readings.

[nomoresonys]

Re: Samsung UN55KU6300FXZA

Pin 6 seems too low, thinking it should be around 3.3 or so.

[R_J]

Re: Samsung UN55KU6300FXZA

Check the voltage on one of the main filter caps, (CP807) In standby it should read around +160v, when the power button is pressed it should read over +350v. The way the 13v is droping suggests to me the PFC circuit is not working.

[iliketofixstuff]

Re: Samsung UN55KU6300FXZA

Okay, so, thanks again to all so far for the help. I appreciate everyone's time.

I tested the two requested things tonight:

Filter caps:
I tested this with the two boards (power supply and processor) connected.
Measured main filter cap (CP806) with unit plugged in: 390V DC
Pressed the power button, and no change (390V).

CNM803 connector from power board to processor (main) board. This was done with the CNM803 connector disconnected (so the main board is not connected to the power board). All measurements here WRT pin 12 GND. Also, I pushed the power button each measurement even though both the IR receiver and the P function board plug into the main board (which was disconnected for this test). So I didn't see any change.

Pin / Signal / Reading Off / Reading On / Note/Comment
1 / FAIL COUNT / 0 / same /
2 / ANA DIM / 2.36 / same / steady
3 / A13V / 8.9V to 14 / same / about 1s period
4 / OD ON/OFF / 2.5 to 4 / same / about 1s period
5 / A13V / 8.9V to 14 / same / about 1s period
6 / PWM BLU / 2 to 3.5 / same / about 1s period
7 / A13V / 8.9V to 14 / same / about 1s period
8 / POWER ON / 2.8 to 5 / same / about 1s period
9 / A13V / 8.9V to 14 / same / about 1s period
10 / GND / not measured / not measured
11 / GND / not measured / not measured
12 / GND

Recorded a video to illustrate the oscillation period seen on A13V: https://www.youtube.com/watch?v=f4G6KOTJ1z0

Seems to me that with no load on the board the voltages should be pretty well regulated.

Also finally attached a picture of the entire system. Sorry, probably would have been good to have that from the start.

Hope this helps to provide info to assist with diagnosis.

[R_J]

Re: Samsung UN55KU6300FXZA

Just a note: if the main board is disconnected from the power supply, pushing the power button will have NO effect as the main is disconnected.
Knowing this, The power supply board has pullup resistors to turn the power supply ON with the main disconnected, that is why you have +390vdc on the main caps. This means the PFC circuit is working. Have you tried disconnecting the plug going to the backlights to see if the A13V becomes steady?

Another thing you could try is short the POWER_ON pin to ground, this will turn OFF the power supply so the A13V should be steady (and the main cap voltage will drop to 160v)

Have you checked the solder side of the board for poor solder connections on the transformer, and any diode/fets mounted to any heatsinks?

[budm]

Re: Samsung UN55KU6300FXZA

BN44-00807A
https://assets.shopjimmy.com/media/c...00807a-top.jpg
When this power supply is in standby mode (PS-ON not present), the A13 will be about 8V, when PS-ON is present then it goes up to 13V.
You may want to inspect all the solder joints, especially around the transformer legs.

[iliketofixstuff]

Re: Samsung UN55KU6300FXZA

I haven't really checked every solder joint but the couple times I've been on the solder side of the board I remember thinking everything looked well wetted. I may give it one more look just to be sure. I do remember there seemed to be a lot of coating on the solder side which I thought was gross.

My first post wasn't perfectly clear, but I think at some point I checked voltages with the main board disconnected and then both with/without the LEDs connected. I will probably go back and double check that measurement tonight also.

I didn't really know about the pullup that turns on the power board when I started this. But it seems to me that if the board is 'on' with the main board and display board disconnected (So, there is basically no load at all on the power board) that the voltages should be well regulated. If that's enough to day that this board is faulty, that's good enough for me. I'm not looking for a component level repair.

[nomoresonys]

Re: Samsung UN55KU6300FXZA

Could it be a backlight issue?

[nomoresonys]

Re: Samsung UN55KU6300FXZA

Try heating the powerboard with a hairdryer, be sure and hit all the capacitors, see if tv comes on or any change.

[jermelonzo]

Re: Samsung UN55KU6300FXZA

If everything on the PSU is checking out OK. Then I'd start looking at the mainboard. There are often times when the EEPROM gets corrupted and needs replacing. The EEPROM is where read-only firmware is held. I've attached an image of a common Samsung EEPROM IC. See if shopjimmy sells replacements and solder it in.

Hope this helps!

[Hamie]

Re: Samsung UN55KU6300FXZA

I created a thread on repairing this power supply not so long ago. I think you may have the same problem.

Unsteady output voltages is usually caused by one of the smd diodes failing

[Hamie]

Re: Samsung UN55KU6300FXZA

https://www.badcaps.net/forum/showthread.php?t=90116

Please test that diode in the above thread.

[iliketofixstuff]

Re: Samsung UN55KU6300FXZA

Normally I wouldn't reply to an old thread but it's already resurrected.

I ended up guessing and buying a replacement power supply board online and that did the trick. TV has been working fine for the last year or so. I didn't really dig into the design of the board but I could see even on a DMM that the voltages weren't stable so that seemed like a good guess.

Appreciate everyone's help on this. I totally would have tested/changed out the diode at the time if I had this info. Thanks all!

[Hamie]

Re: Samsung UN55KU6300FXZA

I didn't realise this was an old thread as it was bumped.
Be interesting if you still have the old board to test the part though.

[Ef8hemi]

Re: Samsung UN55KU6300FXZA

Hamie... I have a board doing exactly as described in this thread. Voltages all the same. I did check the diode you suggested. Mine tested ok. I ordered a new board so I guess we'll see.

[distearth]

Re: Samsung UN55KU6300FXZA

Hamie... I have a board doing exactly as described in this thread. Voltages all the same. I did check the diode you suggested. Mine tested ok. I ordered a new board so I guess we'll see.

Did the new board fix it? I'm having a similar issue. Backlight comes on when main board is not connected.