qn75q70rafxza suiciding samsungs

[EazyBone]

These seem to always kill themselves lol.

Okay, I have picture but no backlight. Sort of, backlight randomly comes on for about 30 seconds then shuts off. Right when I turn TV on BL does not come on. I waited and eventually boom backlight on. Then shut off, few minutes later, backlight on boom. Then backlight doesn't come on, but person said if you wait a bit BL and picture comes back and on.

I checked power board, voltages as follows
From PSU to main
PSON 3.4
Vamps 18v
13v 13v

All seem correct.

From PSU to LED driver
All vdrv are 112v steady, as board says for stby (when BL came on this tested at 122 on all pints and all caps on LED driver as well, PSU says this is correct voltage also)
13v 12.87
FB 2.48 (don't know what this is)
Fault .061

From LED driver to main.

16 .015. 15 0
14 0. 13 .142
12 1.32. 11 .169
10 .006. 9 1.407
8 0. 7 2.76
6 1.407. 5 3.2
4 2.76. 3 0
2 .045. 1 0

So I could assume that the BLs work and there isn't a problem since the seem to turn on for a bit and turn off, but maybe that's wrong. Anyone have a clue where I should be doing next.

Feels like PSU is ruled out (correct me if I'm wrong) since voltages seem correct BUT I don't know what FB or fault is, and what would be correct voltage for them.

Thanks all!

Edit ALSO I disconnect main board from PSU and plug in, BL doesn't come on, BUT I'm assuming the main board is needed to send a signal or something. Just an observation. Maybe they should come on?

[petehall347]

Re: qn75q70rafxza suiciding samsungs

bad connection maybe

[Storyteller12]

Re: qn75q70rafxza suiciding samsungs

Samsung TVs will turn the backlights on when mb is disconnected from power supply and plugged in. If it’s not lighting up you have bad backlights or bad power supply. If you have backlight tester you can test lights.

[nomoresonys]

Re: qn75q70rafxza suiciding samsungs

Try just lightly tapping around on the back of the tv and see if the leds come on or blink, it does kind of sound like a bad/loose connection as mentioned, maybe also try heating the electorolytics with a hairdryer and try it, might be one that isn't quite doing what it should.

[Diah]

Re: qn75q70rafxza suiciding samsungs

you wrote.. you have picture but no BL. use torchlight and change the BL setting as low you can and try it again if the the 30 second increase to stay on

[EazyBone]

Re: qn75q70rafxza suiciding samsungs

@ story teller, is this true for Samsungs with LED driver board? I know it's true for the other ones, this is first led driver qled ive seen so I have no reference. How would I even test LED ribbons I of course have a tester.
Also Blu_on is coming from the MB, which is why I have the question

@ Sony I'll try this as well. I've reseated all connections I have access to. What do you want me to heat lol

@diah, that's a good idea. I'll get to menu and turn bl down. Not a bad idea

[Storyteller12]

Re: qn75q70rafxza suiciding samsungs

Yes it’s true even for the TVs with led driver boards. If I’m not mistaken you can disconnect mainboard from psu or disconnect wires from mainboard going to the led driver board it will power backlights on.

[nomoresonys]

Re: qn75q70rafxza suiciding samsungs

@ story teller, is this true for Samsungs with LED driver board? I know it's true for the other ones, this is first led driver qled ive seen so I have no reference. How would I even test LED ribbons I of course have a tester.
Also Blu_on is coming from the MB, which is why I have the question

@ Sony I'll try this as well. I've reseated all connections I have access to. What do you want me to heat lol

@diah, that's a good idea. I'll get to menu and turn bl down. Not a bad idea

Heat the electrolytic caps with a hairdryer for a couple minutes, then try it while it's still hot, just in case it's a marginal cap.

[EazyBone]

Re: qn75q70rafxza suiciding samsungs

@ diah, I have turned down the backlight which was pretty low to begin no change

As a note I disconnected the PSU to LED driver and the fault pin reads 4.5v at plug in. I reconnect the PSU to LED driver and then it reads .058 to 0 and goes back and forth. Is fault similar to BL ERR on Sony?

@story, any combination of disconnect ribbons and clips all combos tried BL doesn't turn on.

@anyone, does anyone know if the LEDs are blue on this TV?

Anyone know how I can test the LEDs with a LED tester?

Edit, I have found how to test them I believe using ribbons. Will put results

[EazyBone]

Re: qn75q70rafxza suiciding samsungs

So I measure each ribbon has 14 LED test points on each each one lights up to 131v per tester.

All seem to be working, yes I know the whole sometimes it's not enough current deal,

So when psu not connected to LED driver fault is at 4.5v and when connected fault is at .056, is there something here? Hints? Thanks

[EazyBone]

Re: qn75q70rafxza suiciding samsungs

I also found this on LED driver board. Says should be 3.3v and its 1.408 with everything connected tv on
They are all zero TV off stby. Maybe I'm onto something here?

1 1.408
2 .002
3 .001
4 0
5 0

[Diah]

Re: qn75q70rafxza suiciding samsungs

take it out the boards lol... who knows you could see issue as the other set... if nothings as i think.. its MB / firmware... you can do after inspect the driver boards the following
1- put the TV in STB and from it you log in Service menu to make hard reset.
2- you force the panel to turn on... by connect the 2 point close the top LVDS socket ... see if the BL will remain ON

[lotas]

Re: qn75q70rafxza suiciding samsungs

I also found this on LED driver board. Says should be 3.3v and its 1.408 with everything connected tv on
They are all zero TV off stby. Maybe I'm onto something here?

1 1.408
2 .002
3 .001
4 0
5 0

This is a connector, control points for connecting the programmer so that you can program micom, and there should be between 1 and 4 pin 3.3 v.
And if the power is too low, the controller will not work, and therefore nothing will work.

[EazyBone]

Re: qn75q70rafxza suiciding samsungs

Haha diah I took the boards out now lol I don't see anything wrong.

I'm gonna see how I can do service menu as I don't have Samsung service remote.

Lotas, oh so shouldn't be any concern then I assume?

Diah I don't know what I'm connecting with 2 point above lvds. Like 2 points on the MB? Jump them?

[lotas]

Re: qn75q70rafxza suiciding samsungs

To power the controller you need 3.3v, it is greatly underestimated, which means 1. the DC/DC converter is not working well (not fixed) 2. At the output of the converter (3.3v) there is a short or low resistance, this can be a diode, zener diode, ceramic capacitors or The controller itself runs out of power (then it should get very hot).

[Diah]

Re: qn75q70rafxza suiciding samsungs

yes need connect them together ... they are to force the panel to power on = force BL to turn on
samsung normal RC enough to log in service menu

[EazyBone]

Re: qn75q70rafxza suiciding samsungs

To power the controller you need 3.3v, it is greatly underestimated, which means 1. the DC/DC converter is not working well (not fixed) 2. At the output of the converter (3.3v) there is a short or low resistance, this can be a diode, zener diode, ceramic capacitors or The controller itself runs out of power (then it should get very hot).

So are you saying the problem is the LED driver board? Since the PSU is giving correct voltages minus the fault, which I'm not sure about. Cause the board says that point should be 3.3v not 1.4.

And diah, I will test this when home again.

[lotas]

Re: qn75q70rafxza suiciding samsungs

13v comes to the board, in order to power the controller there must be a dc/dc converter whose output should be 3.3v.
There is also a controller on the motherboard and they communicate with each other and give commands to each other.

[nomoresonys]

Re: qn75q70rafxza suiciding samsungs

If it's too hard to fix, there's some led driver boards on ebay for around 40 bucks.

[EazyBone]

Re: qn75q70rafxza suiciding samsungs

There is 12.8v coming from PSU to LED driver, there isn't 3.3 v going to the LED driver board from PSU or main board. FB sends 2.4 and scl LED, whatever that is only hits 2.6. I'll search some more voltages in LED driver when I get back. Thanks