Samsung LN46C750R2F/ Sound but No Video

[shamwow]

Hello all. I'm having an issue with my Samsung LN46C750R2F LCD TV. Just recently the picture went out. I still have audio on the TV and when I turn off the lights and shine a flashlight at the screen on an angle - I can see the image. I can change the source without an issue as well.

After reading various threads and viewing a few youtube videos - I concluded that the Backlight Inverter is bad. I purchased a new one from an online retailer and installed it when received. The same issue remained... The retailer even sent me another one in case the original was faulty. The second new inverter yielded the same result.

I have checked the power supply and I do not see any bulging capacitors. The TV powers on without an issue it's just the screen is dark.

I saw a video in which the tech jumps the connector off the power supply in order to power on the inverter. Would anyone be able to provide me with details on how to jump this model's inverter? I suppose if the backlight inverter goes on than the issue is with the mainboard?

I thank you all in advance and look forward to any and all responses.

Cheers!

[budm]

Re: Samsung LN46C750R2F/ Sound but No Video

First, you need to upload good clear pictures of the whole back side of the TV and the boards so we can see what we are dealing with.
Did you replace the Balancer board of the power supply/inverter combination board. The board connected to the lamp socket is the balancer board.
http://www.shopjimmy.com/catalogsear...ng+LN46C750R2F
So which one did you replace?

[shamwow]

Re: Samsung LN46C750R2F/ Sound but No Video

Thanks budm for the response!

Here are the pics as requested:









The only part I replaced was the backlight inverter - piece to the far right in picture #1. It is under the black cover.

[budm]

Re: Samsung LN46C750R2F/ Sound but No Video

That is not the inverter board, the correct name is the Balancer board, it is for balancing the backlights lamp so they run with the same amount of the current.
The light brown board is the power supply/inverter board combination.
I cannot read the P/N of that power supply board, it should be BNXX-XXXXX, we need that P/N.
The common failure on this board is that white rectangular cap in the middle of the board, it is right next to the white fuse.
You need to find out if you do have PS-ON and the BL-ON signal or not first, then you need to check the DCV between the two legs of the main filter caps to see if you do have >360VDC or not when the TV is turned on, if you do then the PS-ON is OK.

[shamwow]

Re: Samsung LN46C750R2F/ Sound but No Video

Thanks for the clarification.

I will get the part number for the power supply.

Sorry but I am a bit unfamiliar with those terms... What do you mean by PS-ON and BL-ON? Power supply and backlight on?

How can I check for PS-ON and BL-ON?

[budm]

Re: Samsung LN46C750R2F/ Sound but No Video

You can do the quick check by measuring the DCV between the two legs of the main filter caps to see if the Voltage is >360DVC when TV is ON, if you do, then the PS-ON (Power supply on) signal form the main board is OK.
BL-ON is the signal from the main board to turn on the backlights circuit.
You should read the basic LCD TV troubleshooting guide (in your case, your TV does not use 24V for the inverter circuit, but the required signals are still the same). You do have proper tools and know about safety when working on the PRIMARY HOT DEADLY side of the circuits, right?

[shamwow]

Re: Samsung LN46C750R2F/ Sound but No Video

I will say that I have never worked on a TV or power supply before.

I have printed out and am reading the Basic LCD repair guide... I do have a Fluke multimeter but do not have an isolation transformer.

I do appreciate the help and guidance as I really do enjoy solving and fixing my own problems.

Perhaps I can take a better pic of the power supply and someone can help guide me in the right direction for measuring the DCV between the main filter caps?

[shamwow]

Re: Samsung LN46C750R2F/ Sound but No Video

Using this thread as a reference: https://www.badcaps.net/forum/showthread.php?t=32881

My unit does have the BN44-00341B Power Supply...



After I disconnected the PS Cable to the Mainboard and supplied power to the TV - the backlight did not come on.

Unplugged the power, reconnected cable and applied power - the TV turns on but no backlight.

Upon closer examination of the PS...



a lil bit closer...



Something not right with CI818 cap...

Hope to order a new one tonight and see how it goes. Any recommendations on a site to order?

[shamwow]

Re: Samsung LN46C750R2F/ Sound but No Video

Having a hard time finding a replacement cap ...

Anyone know where to find the .47uf 450v cap for this Samsung?

Thanks in advance.

[budm]

Re: Samsung LN46C750R2F/ Sound but No Video

Post 4: 'The common failure on this board is that white rectangular cap in the middle of the board, it is right next to the white fuse."
High frequency/current Polypropylene type:
http://www.digikey.com/product-detai...202-ND/1981474

[shamwow]

Re: Samsung LN46C750R2F/ Sound but No Video

Thanks budm... I just checked your link and the specs appear OK but the lead spacing does not look correct. I have the bad cap in hand and the lead spacing that I measure is 15mm...

I also saw you recommend a 630V or higher on another thread. What's the reasoning for that? Thank in advance.

[shamwow]

Re: Samsung LN46C750R2F/ Sound but No Video

http://www.digikey.com/product-searc...art=PCF1607-ND

The two I found that meet the specs... Going to order the one in stock...

http://www.digikey.com/product-detai...606-ND/3844528

Looks ok?

[budm]

Re: Samsung LN46C750R2F/ Sound but No Video

Thanks budm... I just checked your link and the specs appear OK but the lead spacing does not look correct. I have the bad cap in hand and the lead spacing that I measure is 15mm...

I also saw you recommend a 630V or higher on another thread. What's the reasoning for that? Thank in advance.

Higher Voltage rating is better, you can just bend the legs to fit into the board. The power supply Voltage feeding that circuit is around 400VDC so the original one does not have much safety head room.

[budm]

Re: Samsung LN46C750R2F/ Sound but No Video

http://www.digikey.com/product-searc...art=PCF1607-ND

The two I found that meet the specs... Going to order the one in stock...

http://www.digikey.com/product-detai...606-ND/3844528

Looks ok?

They are fine if you want to stay with 450V.

[shamwow]

Re: Samsung LN46C750R2F/ Sound but No Video

Thanks budm...

New caps were sent to my house today... question regarding installation.

Is there a positive and negative side on the cap? I checked the board and did not see an indication of positive or negative.

Thanks.

[shamwow]

Re: Samsung LN46C750R2F/ Sound but No Video

the bad cap I removed had no indication of positive or negative. I know the round tall caps have an indication on them...

[budm]

Re: Samsung LN46C750R2F/ Sound but No Video

No polarity for that cap.

[shamwow]

Re: Samsung LN46C750R2F/ Sound but No Video

Thanks. Hope to report back later with some good news.

[shamwow]

Re: Samsung LN46C750R2F/ Sound but No Video

Just wanted to say thanks to budm for the guidance with my TV issue.

Replaced the CI818 cap with a new capacitor from digikey.com

I used a 630VDC as per budm's suggestion.

MFG P/N --- ECW-FA2J474J

http://www.digikey.com/product-detai...574-ND/3088042


Thanks again! Feels great to have the TV back!

[budm]

Re: Samsung LN46C750R2F/ Sound but No Video

Thank you for the follow-up on the repair.