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Old 04-02-2012, 05:51 PM   #1
blasteroo
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Default dead samsung 940bw

Hi all,

I'm new to this forum and I've got a dead samsung 940bw monitor that went completely dead a few weeks ago, and I was hoping not to give up on it just yet and hopefully bring it back to life.

When I turn the power switch on then hit the frontal power button, a blue led lites and I get a faint grey on the screen, almost unnoticeable.

If it hit the frontal power button again, the blue led shuts off and the screen goes completely black.

I already changed: (2) 1000uf/16v and (2) 1000uf/25v capacitors on the power board with no avail.

I don't want to spend any more money on parts without having a more clear direction where to start from.

Could you help me troubleshoot it?

Regards,

Paulo
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Old 04-02-2012, 05:58 PM   #2
Jasgriff
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Default Re: dead samsung 940bw

Hi blasteroo,

Can you see an image on your screen if you shine a flash light at it?

Does the screen come on normally for a few seconds before turning off?

And welcome to the forum.
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Old 04-02-2012, 06:32 PM   #3
blasteroo
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Default Re: dead samsung 940bw

Jasgriff,

Thank you for the reply and for the welcoming message.

Regarding your questions, the faint grey image (without graphics) is only noticed in a really dark environment. In a well-lit room you can hardly see a change.

The screen doesn't come on at all, except for the faint grey image.

When I press the frontal power button I either get:

- No image + no led light

- Faint grey image with no graphics + continuous blue led light

Best,

Paulo
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Old 04-02-2012, 07:41 PM   #4
blasteroo
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Default Re: dead samsung 940bw

Jasgriff,

I think I understood what you meant when you asked "Can you see an image on your screen if you shine a flash light at it?".

Yes, I can see windows desktop if I shine a flash light really close to the screen.

Any advice?

Thank you,

Paulo
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Old 04-02-2012, 09:56 PM   #5
retiredcaps
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Default Re: dead samsung 940bw

If the backlights don't come on, check for

1) blown fuse in the inverter section
2) shorted mosfets in the inverter section

Both components could be on the back side.
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Old 04-03-2012, 01:53 AM   #6
Jasgriff
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Default Re: dead samsung 940bw

that's good it tells us that its your back light not coming on or not staying on that's the issue.

If you are not even getting a flash of light then this looks like the inverters which drive your back lights are not getting any power at all. This is why retired caps is asking you to check for a blown fuse or mosfet. As he explains these will be on the underside of you main board.

This is difficult to point out without really good clear pics of the top and the bottom of you board.
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Old 04-03-2012, 04:29 AM   #7
blasteroo
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Default Re: dead samsung 940bw

Thank you so much for your help!

Please see attached pic of power board.

I've checked the FH602 and FH601 fuses for continuity with a multimeter
and it seems to be ok.

Could you assist me in testing the mosfets?

Paulo
Attached Images
File Type: jpg samsung_940bw_powerboard.jpg (891.1 KB, 53 views)
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Old 04-03-2012, 08:12 AM   #8
Nocta
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Default Re: dead samsung 940bw

http://www.youtube.com/watch?v=fsdQtcd9tDs

VocÍ fala portuguÍs.

Or

http://www.youtube.com/watch?v=YsJXFLnA62s

PS: Is it me or the plastic BN26-00012A is fried? It look to me that the plastic has been exposed to really high temperatures.
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Old 04-03-2012, 02:23 PM   #9
retiredcaps
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Default Re: dead samsung 940bw

Quote:
Originally Posted by blasteroo View Post
I've checked the FH602 and FH601 fuses for continuity with a multimeter
and it seems to be ok.
I don't recommend using continuity as a good way to reliably see if a fuse is good or not. A good fuse should measure less than 1.0 ohms.

Some multimeters will beep continuous if the resistance is less than 1800 ohms. No fuse is good when the multimeter beeps and the resistance reading is 1795 ohms.

Quote:
Could you assist me in testing the mosfets?
As I mentioned, the mosfets could be on the backside. A procedure for testing is at

http://www.badcaps.net/forum/showpos...4&postcount=19

Last edited by retiredcaps; 04-03-2012 at 02:42 PM..
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Old 04-26-2012, 09:00 AM   #10
blasteroo
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Default Re: dead samsung 940bw

Hi guys,

thank you so much for the help you provided.

I've decided to order a used powerboard from ebay, I've received and installed it today and the monitor came back to life.

All is good now.

It cost me around 19 euros and it solved the issue.

Thanks again for your selflessness and support.

Best,

Paulo
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Old 04-26-2012, 01:13 PM   #11
Jasgriff
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Default Re: dead samsung 940bw

Hi Paulo,

Glad you got it up and running. Shame we didn't manage to get the olf board up and running.
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