Samsung UN48H8000AFXZA No picture Has Sound

[Gladiatorx]

Hi gents,

I was hoping for some guidance with a curved Samsung. It has sound but no picture. Tried too see if back lights are on, did not see anything. Tried the ShopJimmy menu/flashlight screen test could see nothing.

We did get an ebay main board, but when it was installed we didn't even get sound anymore, so suspect it was a bad ebay board. I've attached pics of the inside of the tv. There s hardly any voltage info to go by.

Did some voltage tests on the main board video driver. I put an arrow nest to the two plugs I tested for voltage. I got about 18 volts whether in standby or on. On one of the pins per plug I got about 18 volts. I then disconnected the two plugs and tested on the board again thinking I would still see the 18v and 38v and got 0v.

So not sure what board to look at.

[Gladiatorx]

Re: Samsung UN48H8000AFXZA No picture Has Sound

I forgot to add the model no is a Samsung UN48H8000AFXZA

[dskall]

Re: Samsung UN48H8000AFXZA No picture Has Sound

What voltages do you get on your cnm803 connector?

[attainteddragon]

Re: Samsung UN48H8000AFXZA No picture Has Sound

pin 16 of cnm803 is your power on command from the main board. does it change states when you try to power the set on?

[Gladiatorx]

Re: Samsung UN48H8000AFXZA No picture Has Sound

Attached are the voltages.

Also pin 16 on standby is about .12V then goes to 3.31v on power on

[dskall]

Re: Samsung UN48H8000AFXZA No picture Has Sound

In a dark room do you see any flash of backlights when first powered on? And you don't see anything on screen if you push menu button with flashlight.

[attainteddragon]

Re: Samsung UN48H8000AFXZA No picture Has Sound

your main and ps are good. now see if you can get some readings off of cn802.

as dskall mentioned, we are now looking towards the backlights.

[Gladiatorx]

Re: Samsung UN48H8000AFXZA No picture Has Sound

No flash of backlights, no menu with flashlight

Attached are the CNL802 voltage readings

[attainteddragon]

Re: Samsung UN48H8000AFXZA No picture Has Sound

might be time for some good pics of the under side of the ps board.

[Andrew F. Ali]

Re: Samsung UN48H8000AFXZA No picture Has Sound

This is atypical backlight issue. LEDs are open on strips. On plug with backlights did connected the LED driver did what it was supposed to do - Shutdown.

[Gladiatorx]

Re: Samsung UN48H8000AFXZA No picture Has Sound

I can take some pics of the boards underneath.

So even one bad led would not allow it to show picture?

Would there not be some kind of test to do at the driver to see if voltage goes up, then comes down?

I was just a bit trying to avoid opening the tv up to the leds.

[Gladiatorx]

Re: Samsung UN48H8000AFXZA No picture Has Sound

I dont suppose there is any way to activate the backlights without disassemble?

Also, On the driver board I testing again, to see if the tv would go into a shutdown mode, by applying voltage to CNL802, then backing it down. I saw no indication of this.

[Gladiatorx]

Re: Samsung UN48H8000AFXZA No picture Has Sound

Attached are pics of the back of the power supply. The main borad only has traces on the back side with nothing visibly burned out.

I still need to pull the tCon board out to get those pics.

[dick_barton]

Re: Samsung UN48H8000AFXZA No picture Has Sound

What voltages do you have on CNL822 pins 22, 24, 26 & 9?

[Gladiatorx]

Re: Samsung UN48H8000AFXZA No picture Has Sound

Before, I reassemble the boards since I have taken 2 out for pics of the back of the boards, any other comments regarding further dis-assembly to check the actual led strips?

I was hoping not to go there, but will, if there is no other way of testing them.

[Gladiatorx]

Re: Samsung UN48H8000AFXZA No picture Has Sound

So I took another look at what it would take to remove the screen on this curved tv to get to the backlights and boy...what bothers me is the curved screen when it's taken out and it flexing and cracking.

I'll post tcon back in a few min.

[Gladiatorx]

Re: Samsung UN48H8000AFXZA No picture Has Sound

T-conn Pictures attached. The black pad on back of T-conn is not removable.

[budm]

Re: Samsung UN48H8000AFXZA No picture Has Sound

You have 16 strings of LEDs with 16 PWM controlled Power MOSFETs for the Cathode return. I would expect that you will at least see some of the LED strings light up before going into shut down because it has 16 circuits so some should come on before the protection kicks in.
The LED Voltage as printed on the board is shown as 34V 2400mA so it does look like the Anode feeding Voltage is OK, and all the Cathode return pins are all showing around 17.5V or so. I seems to me that those MOSFETS are not being turned on.
Something like this the LED string should be check with the tester first.
Has any one fine any fast track for this model? I hate to see panel get damaged during taking or putting it back together.
I think something else is stopping the backlights to come on.
BTW, did you try disconnecting the cable between the main board and the power supply board and then power up the TV to see if you get backlights (it may need dim control signal too).

[Gladiatorx]

Re: Samsung UN48H8000AFXZA No picture Has Sound

Hi BudM thanks for the input. What did you mean by this?

"Has any one fine any fast track for this model?"

I didn't try to disconnect the cable between the boards yet, I can do that in a few min. When I do that normally would the backlights stay on or come on and go right out?

Also you mean just disconnect the ribbon cable only on the side I have the red arrow pointed to?

[budm]

Re: Samsung UN48H8000AFXZA No picture Has Sound

Most of the newer Samsung allow you to do the self test of the power supply/LED driver board by disconnecting the cable between the power supply and the main board, so when you power up the power supply board if the LEDs and the power supply board are OK then the backlights will come on and stay on as long as the TV is plugged into the out.
The SAMSUNG fast track is the trouble shooting guide to help narrowing down to find out which board is bad.
See PDF of fast track sample.
Try the main board side first then try the one on the power supply end.