[simonpaul64]

My TV (a Samsung le46m87bdx 46inch model) has started to intermittently dim the picture on the bottom 65/75% of the screen. With no warning the area goes dark so I can see the picture but not as bright as it should be. It seems like that is a problem with the ccfl tubes, but the area I am talking about must involve several of the tubes. I could understand one tube going wrong – but this is several all at once. The picture will return to normal within a few moments and this might continue to happen for up to a minute, then back to normal. This might not happen again for several days. Could this be the inverter starting to go wrong?

Any thoughts gratefully received. I’m trying to decide whether this could be economically repaired. I already one sale of goods act argument with the retailer and Samsung over this TV (the capacitor clicking issue), so honestly I wouldn’t be sorry to see the TV go – but I suppose I should repair it if it makes sense.

The diagram below is supposed to show roughly where the problem occurs (paste into notepad to see it in a fixed font). The B section generally remains bright and the D section is what dims. If anything the left hand side of the D section is dimmest. The B section yesterday did the same thing – so I think the problem is progressing.





------------------------------------------------
|BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB|
|BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB|
|BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB|
|BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB|
|DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD|
|DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD|
|DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD|
|DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD|
|DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD|
|DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD|
|DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD|
|DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD|
------------------------------------------------

[Nigel Goodwin]

It sounds like the LCD panel requires replacing, CCFL tubes or not, they aren't generally available as a spare, and are difficult to replace even if you can get them.

[simonpaul64]

Quote:

Originally Posted by Nigel Goodwin

It sounds like the LCD panel requires replacing, CCFL tubes or not, they aren't generally available as a spare, and are difficult to replace even if you can get them.

Sounds like a write off then. Thanks for coming back to me...

[chenks]

is it like this? http://www.youtube.com/watch?v=qd1wGwf8LcY

[coachtrip_fan99]

Quote:

Originally Posted by chenks

is it like this? http://www.youtube.com/watch?v=qd1wGwf8LcY

that doesn't sound anything like what the OP described?!

[chenks]

Quote:

Originally Posted by coachtrip_fan99

that doesn't sound anything like what the OP described?!

ignoring the colours, it shows part of the screen going wrong.
however, why don't we leave it for the OP to respond.

[coachtrip_fan99]

Quote:

Originally Posted by chenks

ignoring the colours, it shows part of the screen going wrong.
however, why don't we leave it for the OP to respond.

Quote:

My TV (a Samsung le46m87bdx 46inch model) has started to intermittently dim the picture on the bottom 65/75% of the screen. With no warning the area goes dark so I can see the picture but not as bright as it should be.

.... OK then. we will wait for the OP to respond.

[ProDave]

Interesting fault.

The ccfl tubes on some sets seem unreliable and / or prone to early failure. However when the fail they fail.

your problem you say comes and goes. so to me it sounds like a connection problem, rather than the tubes themselves.

Not that it helps you as to fix a duff connection still requires stripping the panel down which is not for the faint hearted and you can never be certain that you won't damage something else, like the fragile connections to the panel itself.

On some Samsung sets, the inverter connects directly to the tubes via a series of "prongs" on one edge of the inverter board. That might be repairable.

Do you hear any arcing or fizzing when the fault shows? or do you get an ozone smell?

What makes this very interesting is most inverters have protection circuits that shut the whole inverter down in the event of a tube fault, so for me the odd bit is why does it carry on working at all?

P.S my humble opinion is that you tube video shows a set with a tcon or panel electronics fault, not a tube fault.

[brillopad]

Quote:

Originally Posted by Nigel Goodwin

It sounds like the LCD panel requires replacing, CCFL tubes or not, they aren't generally available as a spare, and are difficult to replace even if you can get them.

To satisfy my curiosity I took apart a faulty Samsung panel to see how easy it might be to replace the CCFL tubes.
The tubes are similar in size to spaghetti and just as brittle.
I use the panels commercially and the chance of getting a tube and actually fitting it without creating further damage means I chuck them away.
Panels are mostly Samsung and I buy an LG TV - throw away all the TV bits and just use the panel.

I hate LCDs as they are a pig to try and repair if the fault is more than a failed cap of FET - I've got a collection of boards which failed to cure problems and I don't intend to add to it.

I mostly repair CRT monitors which some folk might think to be spawn of the Devil but they are much easier than LCD.

[simonpaul64]

Quote:

Originally Posted by coachtrip_fan99

.... OK then. we will wait for the OP to respond.

Sorry for the delay. No it isn't what mine is doing. Mine dims in a certain section although the picture is still there, just dark in that section (really just what you imagine if the ccfl tubes were turned off or flickered like a household Fluorescent tube).

[simonpaul64]

Quote:

Originally Posted by ProDave

Interesting fault.

The ccfl tubes on some sets seem unreliable and / or prone to early failure. However when the fail they fail.

your problem you say comes and goes. so to me it sounds like a connection problem, rather than the tubes themselves.

Not that it helps you as to fix a duff connection still requires stripping the panel down which is not for the faint hearted and you can never be certain that you won't damage something else, like the fragile connections to the panel itself.

On some Samsung sets, the inverter connects directly to the tubes via a series of "prongs" on one edge of the inverter board. That might be repairable.

Do you hear any arcing or fizzing when the fault shows? or do you get an ozone smell?

What makes this very interesting is most inverters have protection circuits that shut the whole inverter down in the event of a tube fault, so for me the odd bit is why does it carry on working at all?

P.S my humble opinion is that you tube video shows a set with a tcon or panel electronics fault, not a tube fault.

Thanks for this. I googled the inverter connections and although I know diddly about inverters (or TVs really) it looks like the connections are split out so you get horizontal sections lit by each ccfl. If that is correct it seems that a number of connections (the prongs) are all showing the same fault. That seems unlikely. IF on the other hand Samsung had two inverters (one for the top third of the screen the other for the bottom two thirds of the screen) then I would have a good clue why the bottom two thirds is affected.

No arcing or buzzing - just the sound of the wife whining to make me "fix it".

I'm very close to binning the TV. For a few hundred quid I can get something to replace it (probably not Samsung). Should I be advertising/donating the old one for spares? Anyone near Essex?

[Nigel Goodwin]

Quote:

Originally Posted by brillopad

To satisfy my curiosity I took apart a faulty Samsung panel to see how easy it might be to replace the CCFL tubes.
The tubes are similar in size to spaghetti and just as brittle.
I use the panels commercially and the chance of getting a tube and actually fitting it without creating further damage means I chuck them away.

You can obtain tubes for some Sharp LCD panels, and they aren't too bad to change either.

However, on the minus side, they commonly fail and need replacing - whereas it's pretty rare to get a tube failure in other makes.