Samsung LN40B610A5F backlight problem

[tech2014]

Hey guys, I have a Samsung LCD TV with a backlight problem. When the tv is powered on, the chime comes on and the screen flickers for a second then nothing. The backlight comes on momentarily. When I do the flashlight test, I see no video.

I reflowed the solder on all of the transformers and most of the parts on the heat sink. I also get 390V at the main filter caps, so PFC seems ok. I also get 4.7V on the INV ON/OFF pin and I get 5v and 13V. Would this be a board issue or a bad bulb?

[dick_barton]

Re: Samsung LN40B610A5F backlight problem

Schematic attached.

[tech2014]

Re: Samsung LN40B610A5F backlight problem

I found on another thread that if I short pin 2 of UI801 to ground, the backlights should come on if the inverter board is good, so it may be bad lamp connection or bad CCFL bulb.

I also put the tv in service mode and checked the test patterns and I don't see any signs of a bulb problem.

[ReeceyBurger123]

Re: Samsung LN40B610A5F backlight problem

Unplug the mainboard see if the backlight comes on. Possibly the branch out connectors going to the lamps have worn contacts.

[tech2014]

Re: Samsung LN40B610A5F backlight problem

I tried unplugging the main board and the backlights come on now. I tried this before and it didn't work.

[ReeceyBurger123]

Re: Samsung LN40B610A5F backlight problem

So that means its the Psu/inverter. Remove it and add fresh solder to the lamp connections they tend to break down over time.

[tech2014]

Re: Samsung LN40B610A5F backlight problem

ok I cleaned them and added solder and still no backlights

[tech2014]

Re: Samsung LN40B610A5F backlight problem

so would this be a problem with the power/inverter board or a bad bulb connector or bulb.

[budm]

Re: Samsung LN40B610A5F backlight problem

The Boosted Voltage stays at 390V and did not dip down below 360VDC?
BTW, the high Voltage winding of the inverter transfomers tested OK?

[tech2014]

Re: Samsung LN40B610A5F backlight problem

I tested the transformers and they were fine. Yes, the PFC voltage did stay at 390V. I also tested the ESR of all the caps and they were all fine.

[dick_barton]

Re: Samsung LN40B610A5F backlight problem

Have you checked the voltage on Pin 16, ENABLE of the SEM2006
Enable => 2.0V

[tech2014]

Re: Samsung LN40B610A5F backlight problem

Its 4.36V on pin 16

[dick_barton]

Re: Samsung LN40B610A5F backlight problem

Dam it, so Enable to the chip is fine.

[tech2014]

Re: Samsung LN40B610A5F backlight problem

I am trying to decide whether or not to replace the inverter board first, but what are the chances that it could be a problem with one of the lamp connectors or a bad lamp itself?

[ReeceyBurger123]

Re: Samsung LN40B610A5F backlight problem

Never.... Sounds like its possibly got an intermittent connection in the screen between the lamps they just clip into each other. What does the error pin do when it fails ?

[tech2014]

Re: Samsung LN40B610A5F backlight problem

I assume you are referring to the CCFL inverter driver IC. What pin number?

[dick_barton]

Re: Samsung LN40B610A5F backlight problem

I had a problem with the backlights on a Samsung set recently and the backlight tester sorted out the problem really quickly. 2 tubes not lighting however the backlights were coming on. Testing the tubes using the tester showed them all come on so I knew it was not a tube problem. Soldered up the HV transformer that ptovided the HV to the tubes and fault fixed.
The unit saved me from having to open up the set to get at the tubes to check them out.

Bought cheap from Ebay but you do need a power supply to go with it and I already had a suitable one available.

CCFL LCD BACKLIGHT LAMP TEST TESTER 12V-24V DC INPUT 3" inch TO 55"

[tech2014]

Re: Samsung LN40B610A5F backlight problem

thanks dick_barton, I should invest in one. I measured the voltage on pin 17 (FAIL) and it measured 0.66V

[neilc6]

Re: Samsung LN40B610A5F backlight problem

I have the same model. The backlight flickers and does stay on for about 15 seconds and I can see a pinkish glow from one of the bottom ccfl bulbs. Is that a sign of a failed bulb?

Transformer impedance tested ok but I added fresh solder anyways with no improvement. PFC voltage is a steady 390VDC. Looks like I will need to take apart the panel to check out the bulb and it's connections.

[diif]

Re: Samsung LN40B610A5F backlight problem

I have the same model. The backlight flickers and does stay on for about 15 seconds and I can see a pinkish glow from one of the bottom ccfl bulbs. Is that a sign of a failed bulb?

Transformer impedance tested ok but I added fresh solder anyways with no improvement. PFC voltage is a steady 390VDC. Looks like I will need to take apart the panel to check out the bulb and it's connections.

The pink glow does indicate a failing ccfl.