Samsung TV - no backlight, except when mainboard disconnected

[nomoresonys]

Re: Samsung TV - no backlight, except when mainboard disconnected

OF COURSE resistors can fail short: https://www.allaboutcircuits.com/tex...lure-analysis/

[diif]

Re: Samsung TV - no backlight, except when mainboard disconnected

OF COURSE resistors can fail short: https://www.allaboutcircuits.com/tex...lure-analysis/

Have a read of this, there's no need for the all caps. https://www.eevblog.com/forum/beginn...-do-they-open/

They go high resistance or fail open in my experience.

[lotas]

Re: Samsung TV - no backlight, except when mainboard disconnected

And there are "they" (resistors) with low resistance and the multimeter will show a short circuit.

[nomoresonys]

Re: Samsung TV - no backlight, except when mainboard disconnected

have a read of this, there's no need for the all caps. https://www.eevblog.com/forum/beginn...-do-they-open/

they go high resistance or fail open in my experience.

i will put all caps wherever i feel it necessary but thanks for sharing your opinion, its definitely worth what i paid for it.

[Bigfoot]

Re: Samsung TV - no backlight, except when mainboard disconnected

Hi guys
I'm working on similar Samsung TV UN60J6200AF.
When I plug in power cord, the red light lights up.
I measured on the power supply board, and even without pressing the power on button in getting on CNM803 (which goes from Power supply to Main board):

UD = 2.3V
PMW_BLU4 = 3.3V
PS_ON = 4.4V
A13V = 12.75V

I looked at the manual and all the voltages are correct.
When I unplug the main board from the power supply, LED lights are supposed to come on. However, non do come on.

I then measured at the LED connector CNL802:

D+ to D - = 419V

And yes, that's 419VDC lol.
Is it safe to assume all my LEDs are burnt? Also CNL802 only has one positive and one negative connection. I'm assuming all the LED strips are connected in series.

Should I try to light up the LEDs with a tester next to verify they work?
Any other ideas what to try? Why is the DC voltage so high, is that normal?

This is the first time I have ever opened up a TV, but it's a lot more fun than just junking it.
All your help is much appreciated.

[Rajnhl]

Re: Samsung TV - no backlight, except when mainboard disconnected

check LEDs with tester. I think they are all burnt. 419 vdc s too high.check for a mosfet on solder side, i think D- is not directly grounded.

[Bigfoot]

Re: Samsung TV - no backlight, except when mainboard disconnected

Thank you, I will check LEDs today.
Correct D- is not grounded. Non of lines on the connector are grounded, which I thought was very strange.

But why do you think i immediately have fully operational voltage even when on standby mode? Bad main board perhaps?

[stefanodave]

Re: Samsung TV - no backlight, except when mainboard disconnected

Hi,

I am troubleshooting a Samsung ue48h6400aw. When plugged normally, trying to turn it on leads to blinking power light 7 times and no backlight. If I press buttons I see the corresponding power light flashing (that it acknowledged the action).

If I unplug the mainboard from the power board and plug in the TV, the backlight turns on.

Does this mean it's 100% the mainboard and I should replace that? Or it could still be the power board?

Would appreciate any input, thanks!
-Gil

hi, i have same your problem but with another tv samsung UE55H6670SZ

you have solve? Thanks

[nomoresonys]

Re: Samsung TV - no backlight, except when mainboard disconnected

@stefanodave. Start a new thread since you have a different model, read this: https://www.badcaps.net/forum/showthread.php?t=39740