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Old 01-16-2022, 07:00 PM   #41
nomoresonys
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Default Re: Samsung LE40m87BD ... no backlight

First do this: One of the first and least expensive things you can do when you have an issue is take the powerboard out of the tv, flip it over and look the solder joints over with a magnifying glass if needed, add a little flux to make the solder flow well and add solder to any joints that look even a little suspect. You can practice on a scrap pcb board if needed, careful not to bridge any joints, and always let the board sit for quite a while or discharge the big caps with an appropriate resister before working on it (safety first) to try to keep from getting shocked, it doesn't take 1000 volts to KILL, a lot less can kill, so be careful, it's only a tv.
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Old 01-16-2022, 07:26 PM   #42
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Default Re: Samsung LE40m87BD ... no backlight

Then with tv unplugged check the fuse on the inverter board ssb400ha20v, then if you want to, follow this video at your own risk, there's more on youtube also, heed the warning at start of video 1000 volts can KILL instantly: https://www.youtube.com/watch?v=oE6K4xBVweA
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Old 02-20-2022, 03:47 PM   #43
goodpsusearch
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Default Re: Samsung LE40m87BD ... no backlight

Now that my other project is done ( https://www.badcaps.net/forum/showthread.php?t=102608 ) I think I am ready to try and fix this TV.

I will let you know about it. Wish me luck.
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Old 02-20-2022, 03:59 PM   #44
nomoresonys
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Default Re: Samsung LE40m87BD ... no backlight

check that video in post #42.
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Old 02-20-2022, 04:15 PM   #45
goodpsusearch
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Default Re: Samsung LE40m87BD ... no backlight

watched it carefully and I think this also talks about same kind of failure and troubleshooting steps:

https://www.youtube.com/watch?v=Dh01ZepjDp0

currently watching it
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Old 02-20-2022, 05:07 PM   #46
nomoresonys
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Default Re: Samsung LE40m87BD ... no backlight

For sure thats the other good one, the way he grounds them out til he finds the right one to bypass is the key I think.
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Old 03-05-2022, 07:35 PM   #47
goodpsusearch
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Default Re: Samsung LE40m87BD ... no backlight

Unfortunately, this didn't go well.

First tried the method of measuring AC voltage on every test point of every transformer feedback output and try to find the one that stands out.

Couldn't figure out the wrong one, maybe my multimeter was too slow to catch the peak voltage of the bad ccfl.

Then started shorting test points to ground one by one to find out the faulty ccfl from the test point that when shorted would cause the TV set's backlight to stay ON.

Nothing happened.

Something worth mentioning is that during all those tests I could hear a buzzing sound from ccfl lamps or ccfl transformers during the brief moment the lamps stayed ON. It could be some kind of arcing.

Then started thinking possible explanations of this. Thought of the possibility of more than 1 bad CCFL but the odds of this should normally be close to zero unless something else happened and caused them to go bad.

Anyway, then became impatient and carefully removed the plastic cover with the connectors/sockets off the CCFLs:
https://www.badcaps.net/forum/attach...1&d=1646526089

This was quite revealing (pun intended).

I found 2 physically broken ccfls as you can see on the pics bellow:
https://www.badcaps.net/forum/attach...1&d=1646526089
https://www.badcaps.net/forum/attach...1&d=1646526089

Disclaimer: I have absolute No experience with backlight issues on LCD panels.

Could I have caused this from removing the connector cover?

Could have this been caused due to TV set being dropped / been exposed to extreme physical shock?

Or is it possible that someone tried to fix the TV set before me?

Please notice the burn marks on the ccfl connectors:
https://www.badcaps.net/forum/attach...1&d=1646526089
https://www.badcaps.net/forum/attach...1&d=1646526089
They are NOT on the connectors that connect to the lamps that are physically broken.

Those burn marks could explain the buzzing sound I mentioned above.

At this point I didn't feel I have much to loose so I marked the places of the broken lamps with red lines, then tried to put the connector board back very carefully, because the alignment of all those lamps seemed to be impossible.

Then bypassed the transformers corresponding to the 2 broken lamps, following the YouTube videos posted above, and tried again.

Nothing changed again....

Then had another idea.

Kept the 2 transformers bypassed and at the same time started shorting test points to ground one by one of the remaining ones.

The TV set's backlight finally stayed ON when I shorted the feedback of a CCFL lamp.

Then bypassed this transformer too and let the TV ON for about 20 minutes. I could hear a buzzing sound like arcing again but it was more silent than before. Then, the protection kicked in again and the backlight turned OFF. I cannot say I was shocked when this happened.

Is it safe to suppose that running the set with 3 transformers/ccfl lamps bypassed put bigger stress to the rest?

Or maybe I failed to align properly the CCFL connectors with the cathodes and the silent arcing that I heard caused the cathode to heat up and destroy the CCFL lamp? or just carbonize the cathode and turn it to high resistance?

At this point I cannot even tell for sure if the 3rd CCFL that I bypassed to make the TV set work was indeed bad or just did not align properly to the connector...

I would love to hear from you guys.

Last, but I think this is important:

I found hairline cracks on the plastic Bellow the CCFL lamps (not the connector board), please check pics bellow:
https://www.badcaps.net/forum/attach...1&d=1646526089
https://www.badcaps.net/forum/attach...1&d=1646526089

How can this happen?
Attached Images
File Type: jpg 1.jpg (180.0 KB, 5 views)
File Type: jpg 2.jpg (305.3 KB, 5 views)
File Type: jpg 3.jpg (315.8 KB, 5 views)
File Type: jpg 4.jpg (349.8 KB, 5 views)
File Type: jpg 5.jpg (322.3 KB, 5 views)
File Type: jpg 6.jpg (394.3 KB, 7 views)
File Type: jpg 7.jpg (367.6 KB, 6 views)

Last edited by goodpsusearch; 03-05-2022 at 07:41 PM..
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