Samsung un55mu6500fxza no power

[itronic]

Had no standby light. After opening back up notice that the main fuse was blown On PSU. Unplugged main board cable CNM803 and led cable CNL802 and then Changed fuse and it blew again. So i ordered a new PSU. Board finally came and I installed it. Now i have a standby light . Tv shows to turn on but no backlight. I unplugged the leds cable at CNL802. Test the led string with a led tester. The top set lights up and shows about 110v on led tester. The bottom set lights up and shows about 110v on led tester.
Now i left led tester plugged up to top set and turn tv on. it shows the image and everything but dim. The bottom set plug into led tester and tv set turned on. The bottom led is really dim and you cant see any image. So am wondering is the bottom set down or is the top set brighter then bottom set. Any suggestion.

[itronic]

Re: Samsung un55mu6500fxza no power

These are my boards. no tcon

https://assets.shopjimmy.com/media/c...00807a-top.jpg

https://assets.shopjimmy.com/media/c...07a-bottom.jpg

https://assets.shopjimmy.com/media/c...12037a-top.jpg

[budm]

Re: Samsung un55mu6500fxza no power

Do you get backlights if you disconnect the cable between power supply board and the main board and then plug TV into the AC outlet?

[itronic]

Re: Samsung un55mu6500fxza no power

Thanks Budm for quick reply. No back lights with main board unplugged or when main board is plugin to PSU.

[itronic]

Re: Samsung un55mu6500fxza no power

Anyone else have anything to add on this matter

[neilc6]

Re: Samsung un55mu6500fxza no power

If the backlights appear dim on the bottom half, then you will need to open the panel and visually check the strips with your led tester.

[itronic]

Re: Samsung un55mu6500fxza no power

thank you for the reply. Most tv led strip are cut in half and have same brigtness. I figured thats what it was but wanted to ask you guys first.
Im guessing the old PSU could've blew them when it went bad.

thanks for the help. i will follow up.

[neilc6]

Re: Samsung un55mu6500fxza no power

Odd to see backlight failures in a newer model unless it was a store demo tv. Usually takes 4-5 years on Samsungs so seeing in EH and H series and seeing some posts on J series which should be the progression.

[budm]

Re: Samsung un55mu6500fxza no power

So right now the backlights do not even come on for seconds, correct?
The two LED strings are connected in series, so
1) TV off, Set meter to ba able to read 400VDC. keep Black probe of the meter on the chassis. Put red probe of the meter on 1+ (CNL802 pin 9) the turn the TV while keeping an eye on the meter to see how high the Voltage goes up to and wait 10 seconds to see how low it goes down to, then turn off the TV and repeat the same test on 1- , 2+, and 2-.

[itronic]

Re: Samsung un55mu6500fxza no power

With everything plugged up except power cord.
Black led on chassis red probe on each point and i plug and unplug power cord on each test point and discharge cap to be certain of readings.


Ac plugged in +1 77.1vdc
turn on +1 79.5vdc

Ac plugged in -1 1.15vdc
turn on -1 1.230vdc

Ac plugged in +2 174vdc
turn on +2 176.7vdc

Ac plugged in -2 77vdc
turn on -2 79.5vdc

Also i did the 10sec on each test but it would not change until i turn tv on then off.

[budm]

Re: Samsung un55mu6500fxza no power

Ac plugged in +1 77.1vdc
turn on +1 79.5vdc

Ac plugged in -1 1.15vdc
turn on -1 1.230vdc

Ac plugged in +2 174vdc
turn on +2 176.7vdc

Ac plugged in -2 77vdc
turn on -2 79.5vdc

The 2+ (Anode of the #2 string, this is where the output of the Boosted Voltage of the boost converter is fed to through R9030), the 2 - (Cathode of the #2 string) is connected to the 1+ (Anode of #1 string), the 1 - (Cathode of #1 string) is the connected to the PWM Controlled MOSFET Q9355 which is in series with current sensing resistor R9381 to GND.

I expect the DC V on 2+ to be higher than 176V, if you look at the Voltage chart printed on the board you will see that in 2d mode the Voltage will be 277V @100% Duty cycle, 3d is higher.
Remove the LED connector from the board and check the Voltage at 2+ (or at CH1 which is the leg of R9030) when TV is turned on, it should be higher than 277V.
https://assets.shopjimmy.com/media/c...00807a-top.jpg
https://assets.shopjimmy.com/media/c...07a-bottom.jpg

[itronic]

Re: Samsung un55mu6500fxza no power

led is unhooked

+2 stays at 176vdc when tv is turned on.

[itronic]

Re: Samsung un55mu6500fxza no power

Im guessing since im not getting the recommended 277vdc , the PSU i just brought is down to.

[budm]

Re: Samsung un55mu6500fxza no power

OK the Voltage is not being boosted properly, check the RESISTANCE in both directions of the Diode D9001C, 9002C: you'll need to lift one leg off the board to do the measurement.

[itronic]

Re: Samsung un55mu6500fxza no power

okay thanks i will removed and test. any certain way you want it tested.

[budm]

Re: Samsung un55mu6500fxza no power

okay thanks i will removed and test. any certain way you want it tested.

See post #14.

[itronic]

Re: Samsung un55mu6500fxza no power

Thanks Budm. I was doing checks and found this . Look like this is the problem. The board has a small crack all way down it.
Pic is below

[budm]

Re: Samsung un55mu6500fxza no power

You going to do lots of wire jumpers on that board.
So is this you TV or is it from some one else that worked on it before you?
You should also be able to see the hairline cracked on the top side, this is why it is important to show good clear pictures of the boards.

[itronic]

Re: Samsung un55mu6500fxza no power

This is for a business. So im just going to order another one. I rather it be 100% then messed up. Thank you for all your help. It was really helpful. I will follow up once I recieve PSU board. I will have 2 boards invested in this Tv. Im hoping i can learn what each components does on the board were i can repair it instead of buying board. Would be nice to understand what each thing do and be able to test it better.

History on tv.
Came from a business to be repaired
The first board was down due to the main fuse was blowing.
Second board was post of been new but it has the crack and wasnt putting out the right voltage.
Order new board to replace the previous board waiting on it now.

[budm]

Re: Samsung un55mu6500fxza no power

You just have to learn to section out the board, I.E. PFC section, Stby PS section, LED driver section, etc. and then understand how each section works, it just takes time with lots of readings and hand-on.