Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

[kfitz]

Thanks in advance for everyone's input.

I have a Samsung LED Model UN50EH5000F (version AJ04).

Upon turning the unit on, the backlights quickly flash on, and then stay off. I've used a flashlight to verify there is still a picture on the screen and I can hear sound from the HDMI input.

If I disconnect the cable from the main board (BN96-28946A) to the power supply board (BN44-00668A) the LED backlights DO NOT illuminate.

Here are the voltage readings from the connection at CNM803 when powered ON:

Pin 1 (B13V) = 12v
Pin 2 (P_DIM) = 0v
Pin 3 (B13V) = 12v
Pin 4 (B13V) = 12v
Pin 5 (Vamp) = 12v
Pin 6 (BLU_ON) = 4v
Pin 7 (Vamp) = 12v
Pin 8 (GND) = 0v
Pin 9 (GND) = 0v
Pin 10 (GND) = 0v
Pin 11 (B5V) = 5v
Pin 12 (A5V) = 5v
Pin 13 (B5V) = 5v
Pin 14 (PS_ON) = 3v

Here are the voltage readings from the connection at CNL802 when powered ON:

Pin 1 (D+) no wire = 325v
Pin 2 (D+) = 325v
Pin 3 (S1-) = 4v
Pin 4 (S2+) = 4v
Pin 5 (NC) no wire= 0v
Pin 6 (S2-) = 5v
Pin 7 (S3+) = 5v
Pin 8 (D-) = 6v
Pin 9 (D-) no wire = 6v

Here are the voltage readings from the connection at CNL802 when powered ON and cable to LED backlights is unplugged:

Pin 1 (D+) no wire = 325v
Pin 2 (D+) = 325v
Pin 3 (S1-) = 0v
Pin 4 (S2+) = 0v
Pin 5 (NC) no wire= 0v
Pin 6 (S2-) = 0v
Pin 7 (S3+) = 0v
Pin 8 (D-) = 7v
Pin 9 (D-) no wire = 7v

Any input is greatly appreciated. Thanks!

[dskall]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

For cnl802 did you power it on and off for each pin check and record max. voltage or all at one time?

[dick_barton]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

The legend on the power supply says 229V @ 470mA and you report that the boosted led voltage peaks at 325V, leds flash before collapsing.
Also your readings with the leds connected/disconnected would be indicative of a problem with one or more of the led strings.

What is your panel number as given on the rear of the lcd panel.

[kfitz]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

For cnl802 did you power it on and off for each pin check and record max. voltage or all at one time?

All at one time

[kfitz]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

The legend on the power supply says 229V @ 470mA and you report that the boosted led voltage peaks at 325V, leds flash before collapsing.
Also your readings with the leds connected/disconnected would be indicative of a problem with one or more of the led strings.

What is your panel number as given on the rear of the lcd panel.

Is the rear of the LCD panel this metal chassis in the pictures I attached or would I need to deconstruct more of the television. Trying to figure out where to get the part number. Thanks

[dick_barton]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

I can make some of the label out but not fully due to poor focus.


Edit
It looks like DF500BGA-B1 and if it is then it's made up of 2 interconnected led strips per row totalling 15 leds and 4 rows altogether. (15 * 4 leds)

I suspect they are all connected in series and you have a led(s) fault.

[budm]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

http://www.shopjimmy.com/catalogsear...?q=UN50EH5000F

[kfitz]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

Makes sense. ShopJimmy is out of the DF500BGA-B1 part, but they have alternatives so I'm going to order part T500HVF02.2. Thanks guys, I'll report back. This forum is amazing.

[kfitz]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

Okay, so the backlights came in today. Swapped them out with no problem, but when I test the lights (unplug cable from power board to main board), the lights are not steady. They are flickering. Not totally on and off, but the brightness difference is noticeable enough to consider it a flicker. Any idea what would cause this? I don't want to put the panel back together only to find out I have another issue.

[dick_barton]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

Check all the connection points where the led strips join one another and the side strip. One poor connection could be a cause. If all the leds are in series then another cause is a failing led.

[kfitz]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

All the connections are tight. I even tried using the cable that came with the lights just in case. I also ended up ordering a power board because I found one for $20 on Ebay as a backup in case I also had a P/S or LED driver issue. Same results with the backup P/S board.

[kfitz]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

How would I tell if one of the LEDs is "failing?"

[kfitz]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

Not sure if this helps to troubleshoot, but the new voltage readings from the connection at CNL802 when powered ON:

Pin 1 (D+) no wire = 154v
Pin 2 (D+) = 154v
Pin 3 (S1-) = 78v
Pin 4 (S2+) = 78v
Pin 5 (NC) no wire= 0v
Pin 6 (S2-) = 40v
Pin 7 (S3+) = 40v
Pin 8 (D-) = 2v
Pin 9 (D-) no wire = 2v

Also, when the LED strips are on and flickering, each strip is reading 38v

[kfitz]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

Would you recommend testing each LED?

[dskall]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

I would suggest testing whole strip at a time while still attached to panel

[kfitz]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

hmmm. What would I need for that? I rigged 2AA batteries to test the individual LEDs. Also, when you say "attached to the panel", do you mean leave each strip connected to the P/S board or just fastened to the panel?

[dick_barton]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

You should be able to measure the voltage across each led strip at the point within the red box (on each of the 4 strips) which should be identical and in the region of 1/4 the supply voltage. There may be a "+" and "-" sign within the box for you to take the readings.

[budm]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

Not sure if this helps to troubleshoot, but the new voltage readings from the connection at CNL802 when powered ON:

Pin 1 (D+) no wire = 154v
Pin 2 (D+) = 154v
Pin 3 (S1-) = 78v
Pin 4 (S2+) = 78v
Pin 5 (NC) no wire= 0v
Pin 6 (S2-) = 40v
Pin 7 (S3+) = 40v
Pin 8 (D-) = 2v
Pin 9 (D-) no wire = 2v

Also, when the LED strips are on and flickering, each strip is reading 38v

If you look at the VLED Voltage as printed on the board, it is 229VDC (LOADED), you have 60 LEDS total (4 STRIPS OF 8-LED, 4 STRIPS OF 7 LEDS) = 60 x 3Vf = 180VDC + VDROPS Vdrops on the PWM Controlled MOSFET and the current sensing resistor so 229V is about right for the circuit, you only have 154VDC so something is loading the LED drive Voltage.
Do you still get over 300VDC if the LED string is not connected?
If you look at the Voltage reading between 154 -78 = 76V. 78 - 40 is only 38V, 40 - 2 is also only 38V. I expect both of those two sets of strips to be a lot more than 38V.

[dick_barton]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

+1
In post#1 it is stated that the open circuit led voltage is 325V

[dskall]

Re: Backlight Issue on Samsung LED Model UN50EH5000F (version AJ04)

You can also test your strips with your boards hooked up and your panel off. Press your power button and watch if all strips/leds light up. They will only flash but you can determine if all are working. You can have bad connections between strips that testing one at a time won't find. Also you said they are flickering. What is the voltage across your main capacitor on your power board. The big blue cap and what is the voltage printed on it?