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Old 06-02-2020, 06:21 AM   #41
dronerat
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

Quote:
Originally Posted by budwich View Post
check to see if there is a third led on the tcon. Other threads of samsungs indicate such.
IF so, that is your likely problem.
No third LED on the T-Con only two.
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Old 06-02-2020, 06:30 AM   #42
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

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Originally Posted by budwich View Post
further, you refer to one of the leds flashing ... which one does this?
The one circled with green stays constantly on while the other one circled in red lights up for a second and then goes off when the TV is not working correct. When the TV is working it is constantly ON.
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Old 06-02-2020, 06:47 AM   #43
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

Thanks for the info / clarification. you might have to look under the shield / cover to see if there is a third led.

The leds are associated with voltages on the board and as you have potentially figured, the flashing one is associated with 12v (panel driving) while the solid is associated with 3.3 (logic). Your measurements appear to indicate a potential "excessive load" on the 12v which causes it to "droop".

I have to re-read things, but I think you indicated you had two tcons. Do both respond the same?

My best guess is that you might get lucky with the "tape cutoff" method of stopping certain signal from the tcon to panel. Lots of threads on this method's success. Basically a small piece of tape put on one of the tcon cables (at the tcon) blocks a few of the pins (usually near the one side or the other, 5-10 pins... experiment with positioning).
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Old 06-02-2020, 06:50 AM   #44
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

Quote:
Originally Posted by budwich View Post
I have to re-read things, but I think you indicated you had two tcons. Do both respond the same?

My best guess is that you might get lucky with the "tape cutoff" method of stopping certain signal from the tcon to panel. Lots of threads on this method's success. Basically a small piece of tape put on one of the tcon cables (at the tcon) blocks a few of the pins (usually near the one side or the other, 5-10 pins... experiment with positioning).
I have two T-Cons and they respond the same.
I will try the tape cutoff method.
I will also remove the heatsink on one of the T-Con boards to look for a third LED.
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Old 06-02-2020, 06:56 AM   #45
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

I was not able to find a third LED on the T-Con board
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Old 06-02-2020, 07:31 AM   #46
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

:-( I guess they used a different design in this board. Of course, don't run the tcon with out the heat sink / shield in place.

Based on my reads, there are a number of voltages (operational towards the panel) that are labeled on the tcon. Things like VcomXX, "VDD", etc. It is likely one of those has an issue which causes excessive draws on the supply 12v. Some people have found checking for shorts around those voltages to find potential issues with the subtending circuit, usually a shorted / failing smd capacitor on the bottom edge driver boards.

Last edited by budwich; 06-02-2020 at 07:59 AM..
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Old 06-02-2020, 08:07 AM   #47
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

Quote:
Originally Posted by budwich View Post
:-( I guess they used a different design in this board. Of course, don't run the tcon with out the heat sink / shield in place.

Based on my reads, there are a number of voltages (operational towards the panel) that are labeled on the tcon. Things like VcomXX, "VDD", etc. It is likely one of those has an issue which causes excessive draws on the supply 12v. Some people have found checking for shorts around those voltages to find potential issues with the subtending circuit, usually a shorted / failing smd capacitor on the bottom edge driver boards.
I have checked probably all of the capacitors on the driver boards and did not find any shorted ones.
Probably this evening I will disassemble the set and remove all of the plastic panels around the display to see if there are more things that I can measure.
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Old 06-02-2020, 08:50 AM   #48
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

you should give the "tape cutoff" method a try. It costs nothing and won't damage the set assuming you are careful with the cables and taping.
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Old 06-02-2020, 08:52 AM   #49
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

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Originally Posted by budwich View Post
you should give the "tape cutoff" method a try. It costs nothing and won't damage the set assuming you are careful with the cables and taping.
I will start with that. I don't know with which ribbon cable to start, but I will give both a try
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Old 06-02-2020, 09:59 AM   #50
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

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Originally Posted by dronerat View Post
I have checked probably all of the capacitors on the driver boards and did not find any shorted ones.
Sure enough I have missed one on the buffer boards... Here is the little bugger on the most right point of the right buffer board. It is dead shorted. Here is a picture. It is circled in red.

Now I am not sure what will happen if i remove it and start the set without that capacitor. Or what is the value of this capacitor if I try to find a replacement.

I need to get some tape and try that first. At least now I know which ribbon cable I should try
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Old 06-02-2020, 01:10 PM   #51
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

pull it first... and try a "quick test". Go from the result. Others have removed bad components on the driver for a bit and then ultimately replaced them. The set should function OK. The "tape cutoff" method could work also.... trace the tracks back to the cable to see which pins are involved to give you an idea of where in the cable you can start with.

Last edited by budwich; 06-02-2020 at 01:12 PM..
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Old 06-03-2020, 01:44 AM   #52
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

Quote:
Originally Posted by budwich View Post
pull it first... and try a "quick test". Go from the result. Others have removed bad components on the driver for a bit and then ultimately replaced them. The set should function OK. The "tape cutoff" method could work also.... trace the tracks back to the cable to see which pins are involved to give you an idea of where in the cable you can start with.
Turns out it was the resistor to the left of the capacitor that was causing the short. Removed it, the short is gone but the problem still persists. The TV started twice after that and I have not seen any artifacts/distortions of the picture.
Will get some clear tape to try and cut off some signals.

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Old 06-03-2020, 04:51 AM   #53
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

It might be a "zero ohm resistor"... is there a similar layout on the other half of the tv... ie. the edge board on the other side?
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Old 06-03-2020, 06:47 AM   #54
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

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Originally Posted by budwich View Post
It might be a "zero ohm resistor"... is there a similar layout on the other half of the tv... ie. the edge board on the other side?
I don't see the logic here because that way the capacitor will have both it's pads grounded. You can see the small trace between the resistor and the capacitor. I also managed to lose the resistor.

Nevertheless currently I have managed to fix the set using the "tape cutoff" method and it is working for 4 hours straight with occasional checks if it will start after powering off. Not really sure how long it will last, but that will do for now. If it dies again it will be sold for parts.

I want to thank everyone that gave ideas and tips for debugging. You are such a great community.

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Old 06-03-2020, 07:03 AM   #55
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

good work... glad you got it to function, save it from the dump. The method usually results in a functioning set for a long time (ie. years).
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Old 06-03-2020, 09:30 AM   #56
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

YEP, this right here is why I go to "tape method" first, then work out from there if no joy. Could have had it fixed 2 weeks and 50 posts ago but you learned a lot I'm sure.
__________________
1) https://www.youtube.com/watch?v=4F2J1Dkf4Is
HIGH VOLTAGE HAZARD demonstration. Video by Electronic Doberman.
2) https://www.youtube.com/watch?v=4v8DcqCNG4A
Power supply board voltage testing by shopjimmy.
BE VERY CAREFUL WITH POWERSUPPLY, VOLTAGE ON PRIMARY/HOT SIDE CAN BE DEADLY, THE CAPACITORS CAN HOLD A VERY BIG CHARGE LONG
AFTER TV HAS BEEN UNPLUGGED.
3) 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.
Donations accepted with a smile and a Thank you
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Old 06-03-2020, 09:37 AM   #57
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

The best clue was in your first post, shop said panel is dead, they didn't lie this time.
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Old 06-04-2020, 12:34 AM   #58
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

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Originally Posted by nomoresonys View Post
The best clue was in your first post, shop said panel is dead, they didn't lie this time.
Let me stress on "this time".

I have had bad experience with electronic repair services both official and not official.

The quote for the repair of this TV by an official service was ridiculous. 400 euro for the panel and about 75-100 euro labor. That is more than what the TV was bought 4 years ago.

Had one JVC which was diagnosed with bad main board. Turned out to be a dead LED strip (one LED was shorted and one was opened) Quote by the repair shop was 70 euro for the board and about 30 euro labor. I got a LED strip for 10 euros and replaced it. (I know I should have replaced all, but this TV was stored to be used as a backup so it's ok).

Had one Panasonic Plasma TV that was diagnosed with shorted panel again. Turned out to be blown transistors on the board that is responsible for the horizontal lines(Not sure how it was called probably P-Board it was long ago). It was even a known issue and repair kits were sold, but the repair kit costs more than a board from a dead TV. Total of repairs - 25 euro. This Panasonic is still working happily in my living room 4 years later.

My girlfriend is joking that we will never have a brand new TV at home.

Also had experience with a ridiculous quote from an official iPhone repair center which was about 200 euros for labor, shipping and replacement of the top speaker, which another repair service managed to do for 15 euro.

So all in all I don't really trust repair services either official or not and try and repair the thing until I am convinced that it is not repairable.

The TV is happily working in my bedroom now. The only difference I have found after I used the tape method is that the left side of the screen needs some time to fully light up when the TV is starting. It starts to light up from the center to the left, and it takes about a second for the screen to come up fully. That is no big deal and if you don't know that it should not do that you will never notice.

Last edited by dronerat; 06-04-2020 at 01:53 AM..
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Old 06-04-2020, 04:39 AM   #59
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

Indeed, that is definitely why I put this time, I should have put quotes around it. Some might not agree but I have seen about as many dishonest tv shops as mechanic shops, appliance shops etc. etc.
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Old 06-04-2020, 04:48 AM   #60
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Default Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

There isn't much worse than being screwed by a dishonest repairman, then finding out that you were, most suspect but never realize they were, that's why I diy fix it, if I can't then I buy it new. Think it was an episode of 20/20 or similar tv program that exposed dishonest repairmen, was funny how some of them tried to blame the customer once they were caught red handed.

Last edited by nomoresonys; 06-04-2020 at 05:12 AM..
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