Samsung LN40B650T1F won't power on

[MEB]

Re: Samsung LN40B650T1F won't power on

Update. Talked my friend into taking the back off his Samsung LED to check for obvious. He sent me some photos which I have attached. See nothing obvious to me. If I can get a little help, I will loan him a meter if anyone has any ideas. If I get any help, I will arrange to get more pictures of the boards. Symtoms are, works fine for 5-10 minutes, then loses video. Cycling power button brings back to normal for another 5-10 minutes and so on. Please help me get him started. The TV is too big to smuggle into work!

[MEB]

Re: Samsung LN40B650T1F won't power on

oooooops LCD not LED. Sorry

[tom66]

Re: Samsung LN40B650T1F won't power on

Ask your friend to check the screen in a dark room and see if it remains glowing or if it goes out.

[MEB]

Re: Samsung LN40B650T1F won't power on

Thanks, it is an honor. I emailed him and hopefully will get a timely response.

[MEB]

Re: Samsung LN40B650T1F won't power on

Had my friend power up his TV, shut off the lights and wait. TV had not been on yet that day. About 7 minutes and 40 seconds later screen flickered for a second and then went black. He examined screen as tom66 told him to do and reported absolutely no glow or any light whatsoever from the LCD. Audio works and able to change channels from remote, but screen is black. After cycling the power button, picture came on and appeared normal for about 15 seconds and then went black again. Several more tries, failure was observed approximately 15 seconds each try. I have read about using the flashlight to look into a black screen for repairing monitors to check for image. I guess that would apply to LCD TV's also? I told him to try that when he got home and report back.

[MEB]

Re: Samsung LN40B650T1F won't power on

My buddy called to update that when the LCD screen goes black, and he looked at the screen with a strong flashlight, he could indeed make out moving images. Please answer, at least this question. I really am trying to learn, but obviously my experience is lacking. I think this is telling us that the backlights are not receiving power or are losing the signal from somewhere telling them to stay on?

[Glitcher]

Re: Samsung LN40B650T1F won't power on

I had this model before: Common things that might cause your problem may be a bad transformer, or a bad ccfl lamp.

[MEB]

Re: Samsung LN40B650T1F won't power on

While respectfully waiting for some help, I emailed the following to my anxious friend. I don't know much, but I am trying to learn. Please jump in so I am not misleading him!

OK, Not getting much direction from the forum. We will go on while waiting for them. This is what I know so far. I am not even thinking about the line at the top at this time. We will worry about that later.
-Your Power supply is not dead. Part of it may not be functioning but most of it is. You have Audio (you can hear it) and you have Video (can see with the flashlight).
-Your Main board is not dead. Part of it may not be functioning but most of it is. You have Audio, Video, etc.
-I believe your LCD screen is fine. Not tab related I don't think.
-The problem is your backlights are shutting down. tom66 had us check for glowing I think for T-Con problems, but since you had success with the flashlight test also, maybe T-Con is OK. You have at least 4 (maybe more) CCFL tubes in the LCD Screen which illuminate so you can see the image. The image is there, thus your power and main boards are somewhat functioning possibly even 100%. budm has a test lamp idea I will look into for later.
-The CCFL lamps must have voltage to light and must have an input signal to tell them to light. You are losing power to the lamps or something is causing trouble and the main board is shutting the lights down. What could do that?
-Glitcher says, you could have a faulty or failing lamp which is causing current draw to rise, a faulty or failing transformer which is causing excessive current draw and shutting the lamp circuit down, you could be losing the signal telling the backlights to stay on or you could be losing the main voltage from the power board, to the portion of the main which drives the lamps.
-I really want to help, but I can't do this alone as my understanding of electronics and LCD monitors and TVs is limited so maybe if I post this someone will help us by agreeing or disagreeing with my very basic theories and understanding and direct us.
P.S. If you have an IR thermometer, maybe you can use it to see the temperature difference on the transformers indicated in the attached. See if 1 is running much hotter than the others while we wait for additional help and guidance. If we need to measure some voltages to post replies to suggestions, do you have a digital voltmeter? If not I can find one to loan you.

Hope you can hang on a little longer before taking it in to the shop.

[Glitcher]

Re: Samsung LN40B650T1F won't power on

I read over the thread again, and I think it does point to a failing ccfl lamp. But I would test for all the other possibilities first since its a very delicate task getting to them.

The model I had would turn on for a minute or a couple of seconds and then flicker and go off. I did read somewhere that one of the transformers on this psu would run just a little hotter than the rest. Here's a photo of what I found after I opened up the panel (wasn't easy).

[tom66]

Re: Samsung LN40B650T1F won't power on

At this point I believe a volt meter would be a good idea.

[MEB]

Re: Samsung LN40B650T1F won't power on

Thanks Glitcher and tom66. I will get him a volt meter and/or kidnap his TV, whichever he feels more comfortable with and reply when ready. So from the photo, the LCD screen has 14 backlights or lamps? And the reddish one I guess is not right? Thanks again!

[MEB]

Re: Samsung LN40B650T1F won't power on

My buddy Cal now has a meter to use and surprised as I am, he is ready to dig in. I think he just got bit by the same bug that bit me when I found this site. So if you guys are still willing, we are standing by for instructions! Thanks for spending the time to help us learn. I know this will be a bit challenging for us, but our lack of knowledge should be offset by our enthusiasm. He will keep the TV at his house for troubleshooting and the boards will come to me for component removal/replacement, etc. Thanks again for your knowledge and willingness to help us.

[tom66]

Re: Samsung LN40B650T1F won't power on

OK, see pic attached.

• Set voltmeter to highest DC range, usually 500, 600 or 1000V.
• Note DC is marked with a solid line and a dashed line. Do not confuse this with the AC mark (a squiggle like this: ~)
• Make sure red probe is in VOLT/OHM jack, black probe in COM.
• TV should be turned ON and showing picture.
• On each of the two exposed terminals of the highlighted device, test the voltage.
• I am expecting about 390V with it working. Note HIGH VOLTAGE so be very careful not to touch the terminals, or any part of the power board while in operation or if plugged in.
• See if voltage drops out when the backlight cuts out.

[audiofreak19]

Re: Samsung LN40B650T1F won't power on

Sounds exactly like a bad ccfl bulb. They will turn on initially and if te tv senses a break in connection on a bulb then it will shut the backlight off. I had the same issue with another lcd samsung and if you take the lcd screen out and the diffuser sheets and power the tv on right when the backlight turns on you will see what bulb is not fireing.

[MEB]

Re: Samsung LN40B650T1F won't power on

OK. Thanks so much tom66, do you sleep much? Cal will get home in an hour or so and I will have emailed him picture and instructions. Will get back to you as soon as I can.

And thanks audiofreak19. I will keep your test in mind if/when we get to that point.

[tom66]

Re: Samsung LN40B650T1F won't power on

No work, no university, no coursework, and no one else in the house...

[MEB]

Re: Samsung LN40B650T1F won't power on

Congratulations again on your new job adventure. You must be proud and excited!

[RJARRRPCGP]

Re: Samsung LN40B650T1F won't power on

oooooops LCD not LED. Sorry

Misleading, because "LED" is not a type of screen.

And "LCD" does not mean CFL.

[MEB]

Re: Samsung LN40B650T1F won't power on

Thanks for the enlightenment. I came here to learn, not to be insulted. So while you are so good with letters and abbreviations, you probably know what FU stands for.

[tom66]

Re: Samsung LN40B650T1F won't power on

LED TV is Samsung's misleading term for LED-backlit LCD. Please note this is different from CCFL backlit but only in the backlight. They both have LCD screens and produce near identical picture quality (LED screens have slightly improved colour rendition, and sometimes higher brightness, at the expense of poor contrast.)

I doubt he (RJARRRPCGP) meant any disrespect.