Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

[SherlockGomes]

Hello! I've been lurking here the past few days, and I have finally decided to ask for help because this TV is driving me CRAZY. It's a Samsung UN50JU6500F 4K UHD tv.

The main problem is that there is no picture on the TV, and I hear a ticking sound coming from the power supply about 1 time/sec, with the standby light and t-con board light turning on and off, in sync to the sound coming from the power board. There is no backlights or led turning on either.
I went ahead and disassembled it, and checked the capacitors on the power board, and none of them showed any physical signs of failure, so I tested them all with a multi-meter and they're all charging and discharging properly.
Next, I disconnected everything and plugged in the power board. The 1 click/sec turned into 4 quieter clicks per second.

I've also tested all of the power pins going to the main board and the backlight, and all of the jump and fall according to the clicks, regardless if they are connected to the boards or not.

I've check all the solder point (front and back) for any cracked joint, but I haven't found any.

Attached are pictures of the entire TV back, the power board, pictures of the capacitors (just in case I missed a bad one), and a picture of the power board with a circle around where I THINK the clicking is coming from.

Also, I've included a video to show exactly what the problem looks like: https://youtu.be/HaZCMhuaISM

[FrozenHaxor]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

Can you post a picture of silkscreen near or under the connector that goes to the main board? It should have a little table on it depicting voltages and signal names. If one is present that is.

[SherlockGomes]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

Can you post a picture of silkscreen near or under the connector that goes to the main board? It should have a little table on it depicting voltages and signal names. If one is present that is.

Yeah! Here it is! Sorry for the wait on this.

[FrozenHaxor]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

Please measure voltage on the ON/OFF Pin and also POWER_ON Pin to ground when the TV is plugged in.

Do they fluctuate even when the PSU is disconnected from the logic board and backlight?

[SherlockGomes]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

When I measure the pin, with everything disconnected, it reads between 2.5-3.3v. When it is powered on without being connected to anything, it gives the same voltage.

[nomoresonys]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

Check the solder joints on the transformers, sometimes they look good but aren't.

[budm]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

What happen if you run the power board without have cable to the main board connected?
And yes, check all the solder joints of the power supply board, especially the transformer pins.
https://www.shopjimmy.com/samsung-bn...led-board.htm#

[Diah]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

I went ahead and disassembled it, and checked the capacitors on the power board, and none of them showed any physical signs of failure, so I tested them all with a multi-meter and they're all charging and discharging properly.
Next, I disconnected everything and plugged in the power board. The 1 click/sec turned into 4 quieter clicks per second.

on this test you did.. the backlight should be go on if they are normal.. but it look you have shorted LED on backlight which make the clicks faster.

[SherlockGomes]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

Check the solder joints on the transformers, sometimes they look good but aren't.

I've check and resoldered the transformer joint already, but I'll go ahead and try again. Maybe I missed one.

What happen if you run the power board without have cable to the main board connected?
And yes, check all the solder joints of the power supply board, especially the transformer pins.
https://www.shopjimmy.com/samsung-bn...led-board.htm#

When I run the power supply without the main board connected, the ticking increases from 1/sec to around 4/sec, and the pins read the same fluctuation. With the main board not attached, I still get no backlights.

on this test you did.. the backlight should be go on if they are normal.. but it look you have shorted LED on backlight which make the clicks faster.

Any advice on any easy way to test them? All I have at my disposal, tool-wise, is a multi-meter. I can also get a picture of the pin-outs of the lcd port from the power supply if needed.
EDIT: Also, when I ran the power supply on its own, I really meant in it's own. No backlights attached, nothing. But I have run the power supply with only the back lights, and it still does the 4 clicks/sec, so I'll definitely have to check them out.

[budm]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

Next, I disconnected everything and plugged in the power board. The 1 click/sec turned into 4 quieter clicks per second.
So is that just power supply board by itself and no LED connector in place either, correct?

[SherlockGomes]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

Next, I disconnected everything and plugged in the power board. The 1 click/sec turned into 4 quieter clicks per second.
So is that just power supply board by itself and no LED connector in place either, correct?

Yes, that is correct. Power board with nothing connected to it.

[Diah]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

aha...
you need to put back the PWB in place and fit it with chassis screw and just plug in the BL socket with out MB then plug in and read voltage direct on the legs of 2 caps + legs of 33uf 450V and the - of netter on chassis

[SherlockGomes]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

Ok, after some closer inspection, I believe I have isolated the sound of the noise. Attached is a picture of the source.

[SherlockGomes]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

aha...
you need to put back the PWB in place and fit it with chassis screw and just plug in the BL socket with out MB then plug in and read voltage direct on the legs of 2 caps + legs of 33uf 450V and the - of netter on chassis

Ok, so I measured the voltage like you asked, and both of the 33uf and 450v caps are reading between 89v-92v, fluctuating with the ticking sound as well.

[Diah]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

i don't know if its dark now at your place.. if not took blanket and cover your head and tv together to let it very dark and notice if the BL flicking on a little at time the click

92 v. still low voltagei to feed 2 or 3 channel led strip. when you move the BK socket did you have the same voltage reading ?
if yes.. then put back the BL socket and try heat the PWB then plug it on to check. we need to be sure of PWB first before you go to difficulties BL repair

[SherlockGomes]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

i don't know if its dark now at your place.. if not took blanket and cover your head and tv together to let it very dark and notice if the BL flicking on a little at time the click

92 v. still low voltagei to feed 2 or 3 channel led strip. when you move the BK socket did you have the same voltage reading ?
if yes.. then put back the BL socket and try heat the PWB then plug it on to check. we need to be sure of PWB first before you go to difficulties BL repair

Ok, I followed your instructions, but I still don't see any sign of the back light coming on. I also tried heating the board, too, but to no avail.

[budm]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

This TV has two LED strings (#1 and #2) connected in series to form one large string.
The LED boost converter output is fed to the Anode for LED 2+ pin 1 of CNM803, LED 2- pin 4 of CNM803 is tied to LED 1+ pin 9 of CNM803, LED 1 - (Cathode return of the LED string) pin 12 of CNM803 goes to circuit ground via PWM Controlled MOSFET Q9102C and the Current sensing resistors R9162, 9163 (connected in parallel) to circuit ground.
If you do not have LED connector in place the Voltage on the two legs of the 33uf 450V should jump over 300V (see Voltage chart printed on the board) due to load connected. The 90V you are seeing is the feeding Voltage to the boost converter that step the Voltage up high to drive the LED strings.
The power supply should not be clicking with no LED attached. Is the standby Voltage steady at around 13VDC (as printed on the board)? The power supply boiard has pull-up resistors for performing board self test, without the built-in pull-up resistor for the PS-ON, the standby Voltage will be about 8V (as printed on the board), so if you ground PS-ON pin to ground pin with 100 Ohms resistor, the standby Voltage should be nice and steady at around 8V.
BTW, check the RESISTANCE in both directions of the Diodes D9102C, 9101C
Pictures provided by shopjimmy.

[FrozenHaxor]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

Ok, so I measured the voltage like you asked, and both of the 33uf and 450v caps are reading between 89v-92v, fluctuating with the ticking sound as well.

Is this the voltage of the main input capacitors?

They should have no less than 360-380V with the power supply on.

Please double check that for me. If they fluctuate that far there is an issue with the PFC circuit.

[nomoresonys]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

Ok, so the tics are coming from that transformer, thinking the problem is the transformer itself or somewhere on that circuit.

[lfhlaw]

Re: Samsung UN50JU6500F Blank Screen Boot Loop; Clicking sound can be heard.

Back in March, I stumbled onto this same model of TV that I got for $50. I had to replace the Power board and the TV came back to life for me. I was a bit confused on the PSU testing but figured it out. Eventually the thought was bad voltage regulating diodes on the PSU. But figured it might help you out.

see if any of your symptoms are similar to what mine were.
https://www.badcaps.net/forum/showthread.php?t=75774

my T-con light was blinking and voltage fluctuating (youtube video)
https://youtu.be/G2VdnkdMrPA