Samsung LN52A650A1F no backlight

[NUTIN2LUZ]

Here's another TV that I need help on. A friend of mine gave me this TV because the backlights went out, but there is still sound. I turned it on and there was no backlight. On a different day it worked perfect. Prior to giving me the TV, my friend replaced 2 transistors Q1815 and Q1816 and all the caps. But the problem still happens. You can see the image with a flashlight on the screen. I was thinking of replacing the caps again just to make sure. Also thinking it might be the ccfl. Any thoughts?

[kasfamily]

Re: Samsung LN52A650A1F no backlight

Please photo solder side.Is not CCFL- backlight LED.

[Shinju]

Re: Samsung LN52A650A1F no backlight

Please photo solder side.Is not CCFL- backlight LED.

No, this is CCLF UN are the LED panels.

I have had a few of these, check the 24v on the Power supply for the Inverter side. these power supplies have the inverters built in.

Sounds like you have a toasted inverter transformer or possible shorted FET. Also disconnect the main from the PS and plug the unit in and see if you get backlights.

[kasfamily]

Re: Samsung LN52A650A1F no backlight

Sorry about the mistakes, believed the description of this model on the Internet.

[NUTIN2LUZ]

Re: Samsung LN52A650A1F no backlight

Please photo solder side.Is not CCFL- backlight LED.

First picture are CM851, CM852, CM854, CM855. Second picture are CM856, CM858, CM859. Third and fourth pictures are the transistors Q815 and Q816.

[budm]

Re: Samsung LN52A650A1F no backlight

The inverter does not runs off 24V, it runs on Boosted Voltage from PFC Voltage booster around 390VDC, so verify first that the PFC Voltage is working or not but measuring the DC Voltage right at the two legs of the main filter caps. Check the solder joints on the board real well also.
Also verify that you do have BL_ON signal and Dim signal from the main board.

[Shinju]

Re: Samsung LN52A650A1F no backlight

The inverter does not runs off 24V, it runs on Boosted Voltage from PFC Voltage booster around 390VDC, so verify first that the PFC Voltage is working or not but measuring the DC Voltage right at the two legs of the main filter caps. Check the solder joints on the board real well also.
Also verify that you do have BL_ON signal and Dim signal from the main board.

You are correct, my mistake. I haven't torn into one of these in awhile I just went though a few stand alone inverter panels and got narrow minded!

Budm knows his stuff!

[NUTIN2LUZ]

Re: Samsung LN52A650A1F no backlight

No, this is CCLF UN are the LED panels.

I have had a few of these, check the 24v on the Power supply for the Inverter side. these power supplies have the inverters built in.

Sounds like you have a toasted inverter transformer or possible shorted FET. Also disconnect the main from the PS and plug the unit in and see if you get backlights.

I removed CNI803 and CN801 both from power supply to main board and no backlights turn on. Plugged in CNI803 with CN801 removed no backlights turn on automatic. Plugged in CN801 with CNI803 removed, no backlights turn on automatic.

Where am I suppose to measure the 24v? Do I check them after the inverter as shown in picture?

[NUTIN2LUZ]

Re: Samsung LN52A650A1F no backlight

The inverter does not runs off 24V, it runs on Boosted Voltage from PFC Voltage booster around 390VDC, so verify first that the PFC Voltage is working or not but measuring the DC Voltage right at the two legs of the main filter caps. Check the solder joints on the board real well also.
Also verify that you do have BL_ON signal and Dim signal from the main board.

CP803 & CP804 main filter caps I have 335VDC.

BL_ON 4.88V
DIM 1.117V

Will check all the solder joints on the power supply when I get back home from work.

[Shinju]

Re: Samsung LN52A650A1F no backlight

I removed CNI803 and CN801 both from power supply to main board and no backlights turn on. Plugged in CNI803 with CN801 removed no backlights turn on automatic. Plugged in CN801 with CNI803 removed, no backlights turn on automatic.

Where am I suppose to measure the 24v? Do I check them after the inverter as shown in picture?

Ignore the 24v I was mistaken! Follow budm's steps!

[budm]

Re: Samsung LN52A650A1F no backlight

CP803 & CP804 main filter caps I have 335VDC.

BL_ON 4.88V
DIM 1.117V

Will check all the solder joints on the power supply when I get back home from work.

How about the PS_ON (POWER ON) when switch is activated?
The boosted voltage ON the cap is only showing 335VDC? It should be higher than that per diagram.

[NUTIN2LUZ]

Re: Samsung LN52A650A1F no backlight

How about the PS_ON (POWER ON) when switch is activated?
The boosted voltage ON the cap is only showing 335VDC? It should be higher than that per diagram.

Sorry I've made a mistake at the filter caps. They are 390VDC when powered on and 162.4 when powered off.

PS_ON activated 4.3V

[NUTIN2LUZ]

Re: Samsung LN52A650A1F no backlight

Backlight just went out. I can't seem to see any video in the background with a flashlight.

Voltages when backlights off sound good:

CN801
-PS_ON 4.28V (backlights off, sound good)

CNI803
-ON/OFF 4.86V (backlights on), 4.88V (backlight off, sound good)
-PWM 5.17V (backlights on), 1.119V (backlights off, sound good)

[budm]

Re: Samsung LN52A650A1F no backlight

Please upload the pictures of whole backside of the TV. So the BL_ON is still present, that means the problem may be in the inverter section, the Balancer board, the lamps.

[NUTIN2LUZ]

Re: Samsung LN52A650A1F no backlight

Please upload the pictures of whole backside of the TV. So the BL_ON is still present, that means the problem may be in the inverter section, the Balancer board, the lamps.

Picture of the BL_ON.

[NUTIN2LUZ]

Re: Samsung LN52A650A1F no backlight

After my last post I've checked for cold solder joints and found some. After making those cold solder joints clean I've ran the TV for almost a month and have had no problems. Sold the TV and 12 days later the person that I sold the TV to told me that there is no picture, but the sound is there. He also told me that the screen is black with sound. What else could be the problem?