Samsung LN40B650T1F won't power on

[MEB]

Re: Samsung LN40B650T1F won't power on

Thanks for the explanation. Got my feathers ruffled a bit. Sorry.

Cal called and the meter he borrowed does not go up that high to test the probable voltage you expect, so I am going to deliver mine to him. Will get back with the information later. Thanks for your help and staying with me. It is very much appreciated.

[tom66]

Re: Samsung LN40B650T1F won't power on

It would probably be a lot simpler for you to take the TV to your workbench so we werent't relaying communications over two separate channels, like Chinese whispers things get lost...

[MEB]

Re: Samsung LN40B650T1F won't power on

I know. My only workbench, other than my kitchen table, is not in my home and I can't take TVs to that location. And my friend wants to be involved so it must be the hard way this time. I may explain it more someday.

But anyway, I took my meter to his home and following your instructions,have the following to report. I got to laughing so hard I could barely keep the leads on the capacitor. You said you expected 390V. I saw 389.9 and 390 toggle back and forth and thought, this guy is a genius. I guess I am easily entertained.

But seriously, I got 390V DC at the capacitor and held it there for a minute or so till the backlights shut down and still had over around 390V afterwards. I left an old meter with him so he can measure things for you if I can't be there.

Thanks for helping and I await more instructions when you get time. Thanks again.

[MEB]

Re: Samsung LN40B650T1F won't power on

Have you guys forgotten me?

[tom66]

Re: Samsung LN40B650T1F won't power on

Post got bumped down; missed it. Sorry.

Anyway, as recommended by the previous poster, I would recommend the transformer test. You can do this by running the set until it turns off. Immediately unplug it, and feel each of the inverter transformers. If any one is significantly hotter than the other, there is a fair chance the transformer is bad.

Also, look around for discolouring, damage, etc. around the transformers, in particular any that seems to be focused around just one transformer.

After we think a defective transformer is found there is one final test which should confirm the theory.

[MEB]

Re: Samsung LN40B650T1F won't power on

Thanks. Will do and report back.

[MEB]

Re: Samsung LN40B650T1F won't power on

Called my buddy and he felt each of the 4 transformers and couldn't tell any difference. In case he forgot to calibrate his fingers, I will give him my thermometer, repeat tomorrow and post results.

[Glitcher]

Re: Samsung LN40B650T1F won't power on

Heres a useful video relating

https://www.youtube.com/watch?v=PflyJ4H51Fg

[MEB]

Re: Samsung LN40B650T1F won't power on

Thanks Glitcher, I am at work now and all streaming video capabilities have been blocked by the gestapo, but I appreciate the info and will watch it when I get home.

[MEB]

Re: Samsung LN40B650T1F won't power on

Gave my thermometer to my friend and had him check the transformer temperatures. From top to bottom:
TI801s = 72 degrees F
TI802s = 73.5
TI803s = 74
TI804s = 71
There was no evidence of change from before to after backlight failure. Am confused but very interested in your explanation.

[MEB]

Re: Samsung LN40B650T1F won't power on

I found this on the web then found the same in tom66's schematics. It will help me try to follow along with the future tests for this problem. I know this is elementary to others but what does OPEN1, OPEN4, etc. stand for?

[MEB]

Re: Samsung LN40B650T1F won't power on

Got a chance to watch video suggested by Glitcher last night. Very good stuff for me.

[tom66]

Re: Samsung LN40B650T1F won't power on

OPEN is a signal which will go HIGH (>2V) if a bulb goes open circuit.

[MEB]

Re: Samsung LN40B650T1F won't power on

OK, thanks. Did you see my transformer temp response in post 50? You mentioned one more test before. Could you elaborate?

[tom66]

Re: Samsung LN40B650T1F won't power on

The next step involves putting your multimeter on the 20000 ohm range across the transformers secondaries. For this a picture of the underside (green side) of the power board is required and I or someone else will highlight the secondaries...

[MEB]

Re: Samsung LN40B650T1F won't power on

Thanks for your help. Will get you a good picture and repost as soon as possible.

[MEB]

Re: Samsung LN40B650T1F won't power on

OK,

Here are some photos of the back of the IP board. The ones of half the board may be a little clearer. Am anxious for instructions. Thanks.

[budm]

Re: Samsung LN40B650T1F won't power on

Oh no, you are not supposed to remove that black plastic that has the lamp sockets attached to it, the board is supposed to slide out from the black plastic. I hope the lamps are not broken.

[MEB]

Re: Samsung LN40B650T1F won't power on

Oh No......

I had my buddy remove the board as it is his TV. But in his defense, I would have probably done the same thing as this is the first TV I've been involved with. Thanks for the response and the information. I will determine the damage and reply with the assesment.

[MEB]

Re: Samsung LN40B650T1F won't power on

Thanks budm for the pictures. It is very clear now what should have been done. I now have the board and easily slipped the black plastic piece containing the lamp sockets from the board as it should have been done initially. This is what I feel must happen now.

Continue testing the transformers as tom66 stated. Could someone mark up the board so there is no question as to what to do? I think by reading posts I could do it, but I'd rather be sure.

And I don't see any way to reliably reassemble the sockets to the lamps without disassembling the lcd screen. So I would appreciate any hints, advice, or documentation which might aid in this. I would also like to test all the lamps before reassembly as they were tugged on pretty hard due to the improper removal. Visually the tubes do not appear cracked, but having gone this far, I would want to be absolutely sure. Would it be possible to use a smaller lcd monitor with working backlights to test these much larger tubes? I have plenty of those around.

Any advice would be appreciated. It is almost an obsession now to fix this TV. But at least learning alot in the process. I tried to buy the set from my friend, but he still isn't ready to give up, so I guess I'm in it for the duration if you guys will stick with me. Thanks.