Samsung UN85AU800DF

[Jason616]

TV won’t turn on there is no power light or standby light lit up .

The person I got the tv from said someone told her it’s either a bad board or a bad screen .

How do I tell what I need to replace like a power supply board or main board or the screen itself is bad ?

[EazyBone]

It's either bad power board or bad main board. High chance it's a power board. If you have a multi meter you turn it to beep beep mode (continuity) and check the fuse that's right by the plug. If it doesn't go beep beep then the fuse is blown. Then you know minimally the PSU is bad. Replace it by finding the board model number, usually bn44-xxxxx or bn94-xxxxx. Match that up on eBay or shop jimmy and likely you'll be back in business.

If the fuse isn't blown, then report back and can give more direction.

Not sure if your a newbie to these repairs or not.. can give more details if you are more versed.

[Jason616]

I'm new to repairing TVs
The fuse is good on the power supply board .
I get 13 volts on 4 pins of the connector that plugs in from power board to main board .
i also get 5 volts on 1 of the pins and 1 volt on another .

that's as far as I got since I don't know much about TVs

[EazyBone]

Unplug the main board from the PSU at the PSU connector. Then plug it in. The backlights should come on.

But since you get 13v at the connector, check all the other voltages and make sure they are present. But looking like main board problem then.

[Jason616]

Unplugged main board from power board and no backlights came on

[EazyBone]

Really... That's odd. Back to the PSU, what are all the voltages on the main board connector pins with it disconnected from main. Take closer picture of the legend.

I'm surprised the others haven't chimed in yet

[Jason616]

Pin 1:0.00
Pin 2:0.98
Pin 3:13.09
Pin 4:0.00
Pin 5:13.09
Pin 6:3.06
Pin 7:13.09
Pin 8:5.06
Pin 9:13.09
Pin 10:0.00
Pin 11:0.00
Pin 12:0.00

Please refer to the pic for the pin order

[EazyBone]

Okay now measure the legend for the LEDs. I know you're not supposed to use chassis ground to check voltage, one of the negative terminals there but it says for the 85-in it should be 135 volts. Because the back lights should turn on so something is missing the LEDs it appears or the LEDs are bad. Check the voltage with the PSU disconnected from the lights itself stand around.

[Jason616]

Pin 1:0.00
Pin 2:0.00
Pin 3:273.0
Pin 4:0.00
Pin 5:0.00
Pin 6:273.0
Pin 7:0.00
Pin 8:0.00
Pin 9:273.0
Pin 10:0.00
Pin 11:0.00
Pin 12:0.00

[EazyBone]

TBH I'm a bit stumped. If you unplug the main board from PSU and plug in the backlights should come on.... But you have correct voltages on PSU so not making sense.

But that has nothing to do with the standby light not being on which is the original problem.. but you have voltages from the PSU..

So I don't know how to further assist here. Hopefully someone else can chime in.

I personally would look for voltages leaving the main board near the ribbon and on the buffer boards.. because you have no stby light but you have 13v from PSU. I'm suspecting the main board is bad, which isn't giving you STBY. I'd assume replacing it would fix that issue.

That doesn't explain why backlight doesn't come on though... Maybe they are also bad.. or the PSU is bad running it.. tricky

These are my thoughts. I unfortunately don't know how else to assist more with this sorry.

[lotas]

What is the voltage on this capacitor with the motherboard turned off and the backlight connected? It should be around 135V.

[Jason616]

I get 0.00 volts on that cap with the leds plugged in and the main board disconnected

[EazyBone]

What about with the PSU not connected to LEDs, what's the voltage on that cap

[Jason616]

Without the leds plugged in I get 273 volts measured directly across the cap . With the leds plugged in I get 0.00 volts

[EazyBone]

My advice is to use a led tester and see if they all light up.. $15 on Amazon. That doesn't answer the no stby light still.

Lotas definitely 400x mor advance then me so maybe he has better advice.

[Jason616]

I don’t need to remove the panel in order to test the LEDs do I ?and do you happen to have a link for a good led tester on Amazon ? Sorry just new to all this

[EazyBone]

They all basically work, but heres a link. No panel removal needed to test

So if you look at the legend on the PSU it shows + and - spots for the connection. When you stick the PSU into that white clip. This is where I test them. Stick the probes in-between the white clip parts at + and - spots shown on your PSU. Do not do this with PSU connected! And obviously not doing it on the psu. The voltage will then raise to let's say 80v (random number) and then they should all be 80V and light up. It will show short or a higher/lower voltage such as 100v or 60v on one of the lines then you know it's bad.

For example in your picture, put ground in-between 1 and positive on pin 3. See voltage, then try 2/3 and see voltage. Then move to 4/5 and 6.

Should look like this (random number)

3 80v
6 80v
9 80v
12 80v

Bad would be

3 80v
6 80v
9 300v (short) or 60v
12 80v

These testers are usually safe if you short them out. As a note from experience....!! Don't shove the probes in very hard as you will seperate the contact points of the white clip and then the PSU pins won't make contact making you think something's wrong again! If you have needle probes that will stop it from doing this.

https://www.amazon.com/Backlight-Tes...146&sr=8-4

[Jason616]

Waiting on a led tester to make sure . I used an ohm meter to test black probe leg 1 red probe leg 3 and I get 0.04 ohms did the test on the other pins as well and get 0.03 ohms .

not sure if the ohm meter test works or
not but if so think I have bad leds .

If that is the case is there a safe way to remove the panel since it’s big and very fragile

[EazyBone]

So when you plug in TV and no stby light shows up, did you take a flashlight to the screen? Because sometimes when I plug in Samsung, not always, the TV turns on and no stby light is shown until I turn it off. Have you tried holding power button down after you turn off to get the stby light back? Have you tried turning volume up to hear sound after plugin also?

If it is bad LEDs my suggestion is two people and 4 of these in the picture. They're like eight bucks each from harbor freight. It helps to have two just in case one suction comes off you still have grip on the other. 2 for each person. The biggest I've ever done with two of these and one person was a 75 and it's slightly worries me but I've done it so much now that's no problem. I feel like an 85 would be too much flex and something would happen so I just recommend four maybe someone else has better way but that's how I do it.

Couple of notes that looks like a Samsung from Costco or Sam's they usually carry a 3-year warranty so check on the back of the TV and look at the manufactured date and pray it's 2021 November or later. If it is you can go to Samsung warranty and claim the warranty immediately. They usually come to your house and fix it for free I have done this even without a receipt since they go off the number on the back.

The next thing is that when edgelet Samsungs go bad for LEDs the diffuser shield behind the screen cracks or melts or warps so know that if you replace them you won't know if you're going to have defects until you take off the screen and inspect the diffuser sheet. If that doesn't bother you then carry on if you confirm that it is bad LEDs. The degree of how bad it is really just depends sometimes it's very very minimal with a small bright spot sometimes it's a giant line through the back of the screen that shows up in every picture.

[Diah]

he have Power_ON Pin 8 :5.06V for me are high and the front LED status didn't lit on, it tell there are short ( usually caps ) on MB..
so let see the main boards with out heat sink .