Samsung Syncmaster 940BX backlight problem - Need help please.

[The ENIGMA]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

same here i used an old transformer still problem
guess the other board have the same transformer problem
any hope i do this without a new transformer it is not possible for me to buy it plus coast and repair return

[Randomish]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Good job on the repair.

I suspect the low cost isn't due to low postage prices (although it may be the case), but the cost of the transformer is really low. I recall seeing on a wholesale website that if you buy 100 transformers, they are less than $1 each.

On Chinese websites, such as their equivalent of ebay, I believe the transformers are even cheaper, but since I can't read Mandarin, I can't be 100% sure.

PS. North Amercian sellers charge $19.99 or $24.99 + $6 or $7 for shipping/handling for the same transformer. I suspect they get the parts from the same wholesaler.

There's a great deal going on right now (though slow shipping, since it's in China) ebay lots of 10 TMS92515CT for 18.88 GBP, which is just around 30 US. Since I've gone through 10 monitors already, with caps usually being the issue, it would seem I'll be needing a few of these to fix the remainder.

[retiredcaps]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Total Cost for part including shipping from China....$5.60

Can someone please explain to me how they can ship to me via China Post and US mail for that price?

Good job on the repair.

I suspect the low cost isn't due to low postage prices (although it may be the case), but the cost of the transformer is really low. I recall seeing on a wholesale website that if you buy 100 transformers, they are less than $1 each.

On Chinese websites, such as their equivalent of ebay, I believe the transformers are even cheaper, but since I can't read Mandarin, I can't be 100% sure.

PS. North Amercian sellers charge $19.99 or $24.99 + $6 or $7 for shipping/handling for the same transformer. I suspect they get the parts from the same wholesaler.

[DTLMG]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

I ordered 1 transformer from an Ebay Seller in China...It arrived today, Desoldered the old transformer, put the new one in...WALA..... Monitor working again!

Total Cost for part including shipping from China....$5.60

Can someone please explain to me how they can ship to me via China Post and US mail for that price?

[PlainBill]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

I tried known good CCFL's on monitor 2. and one lights for a couple secs and goes out... the other only half lights.

I have tried the panel on a "test inverter" that I have from a monitor that had a bad LCD and all lamps light.... so im thinking that its prob a bad transformer too. Dam I love this forum. Im not one for waiting... but looks like ill be ordering these from China! LOL...

Any tips on desoldering these buggers?

Everytime I visit my Electronics recycling center and grab all the same type of monitors..they all seem to have the same problems! LOL

Chip-Quik and a little flux. Use the braid to clean up the pads after removing the transformers.

PlainBill

[Th3_uN1Qu3]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Any tips on desoldering these buggers?

Braid and lots of flux.

[DTLMG]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Definitely on monitors on 1, 3, and 4. I'd be suspicious of monitor 2, but that's not as definite. Try swapping the Inverter / power supply from monitor 2 to monitor 4. If that results in one working monitor, replace the transformers on the other 3 and expect a bad CCFL on monitor 2. If swapping I/PS does not work, buy four transformers.

PlainBill

I tried known good CCFL's on monitor 2. and one lights for a couple secs and goes out... the other only half lights.

I have tried the panel on a "test inverter" that I have from a monitor that had a bad LCD and all lamps light.... so im thinking that its prob a bad transformer too. Dam I love this forum. Im not one for waiting... but looks like ill be ordering these from China! LOL...

Any tips on desoldering these buggers?

Everytime I visit my Electronics recycling center and grab all the same type of monitors..they all seem to have the same problems! LOL

[retiredcaps]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Monitor 1
A-B =1.19k
C-D = 2.6k

Monitor 2
a-b = 1.16k
c-d = 1.22

Monitor 3
a-b =6.73
c-d = 1.18

monitor 4

a-b=OL
c-d= 1.27

Am I victim of the transformer issue here too?

Yes. 1.2xy is probably correct. All others indicate that the winding is bad.

Monitors 1, 3, and 4 are definitely bad. 2 is out by more than 3% of each other.

Replacements are probably available ebay. Alternatively, if you don't want to buy replacements, reuse the ones that measure around 1.2xy.

edit: PlainBill beat me again! while I was in calculator mode for the 3% variation.

[PlainBill]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Definitely on monitors on 1, 3, and 4. I'd be suspicious of monitor 2, but that's not as definite. Try swapping the Inverter / power supply from monitor 2 to monitor 4. If that results in one working monitor, replace the transformers on the other 3 and expect a bad CCFL on monitor 2. If swapping I/PS does not work, buy four transformers.

PlainBill

[DTLMG]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

This is a classic example of the 'two seconds to black' problem. Yes, it takes 18 seconds, it still the same problem. The flashlight test is definitive.

There are some discrepancies in your description. It appears this uses four CCFLs, ganged up in two connectors. In the picture of the top you seem to be indicating that one set is not working. Is this correct, or is only one CCFL of four not working?

I've marked up the picture of the bottom. Check the resistance from terminal A to B, C, and D The from C to D. Also, some of those solder joints don't look very good; touch them all up.

I'd say you either have a bad solder joint, or a bad transformer.

PlainBill

Hi guys... do want to beat a dead horse, but

I have four of these monitors all doing the same thing. I measured the transformer as you indicated in this post and my readings are:

Monitor 1
A-B =1.19k
C-D = 2.6k

Monitor 2
a-b = 1.16k
c-d = 1.22

Monitor 3
a-b =6.73
c-d = 1.18

monitor 4

a-b=OL
c-d= 1.27

All caps look fine, i even replaced one board with new Rubycon caps.... Am I victim of the transformer issue here too?

[Ilfirin]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Hello.
I had the same problem on Samsung SyncMaster 940N lcd monitor.
Measured transformator, as is written here, and found C2D resistance about 12k ohm.
Changed transformator and it's working again.

Thank you for excelent instructions

[pamr4]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

On 932MW you can use 2 lamps instead of 4 and it works. The same procedure works on 940.

[retiredcaps]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Anyone have a datasheet on the "famous" TMS91429CT???
I suspect this part is foulty so i need to measure it. Thanks

See this thread

https://www.badcaps.net/forum/showth...ght=TMS91429CT

[Aleksandar]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Anyone have a datasheet on the "famous" TMS91429CT???
I suspect this part is foulty so i need to measure it. Thanks

[Gianni]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Today I received the TRAFO so I finished the job, here some pics.
Following your suggestions I replaced the caps with good Rubycon ZL for 1000uF 25V, Rubycon YXF for a small 47uF 25V. The only one I didn't replace was the input bulk capacitors because I have not such kind of caps but it should be no a problem AFAIK.
The TRAFO has the marking code in black ink on black tape!!! It was hard to verify it was correct.

Thanks again to Badcaps and all members, another good and fast job thanks to the infos posted here.
Gianni


New TRAFO with Ruby ZL



Rubycon ZL



Small Rubycon XYF



Samsung is working again

[PlainBill]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Thanks to this thread I saved time: today I have received a TV Samsung 932MW that stays on for few seconds and then becomes black.
I thought it was due to usual bulging/leaking caps but I was wrong: one secondary of the TMS91429CT is open.

I have already ordered a replacement for 21.4Euro.

On the inverter/PSU board all caps are Samwha rated at 105°C; AFAIK they are not the best caps but they looks good, at least they are not bulging or leaking: do you think I should replace them?

TIA
Gianni

It's your call. IMHO, Samwha caps are overly maligned. Samwha has a serious problem with certain date codes (production runs) of caps failing early. For the most part they are a fine capacitor.

PlainBill

[Gianni]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Well... you are right since the TV is already opened it is better to replace the caps.

Thanks
Gianni

[Th3_uN1Qu3]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Since you bothered to spend money on a new transformer, a couple more $$ for better capacitors won't hurt.

[Gianni]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Thanks to this thread I saved time: today I have received a TV Samsung 932MW that stays on for few seconds and then becomes black.
I thought it was due to usual bulging/leaking caps but I was wrong: one secondary of the TMS91429CT is open.

I have already ordered a replacement for 21.4Euro.

On the inverter/PSU board all caps are Samwha rated at 105°C; AFAIK they are not the best caps but they looks good, at least they are not bulging or leaking: do you think I should replace them?

TIA
Gianni

[hotdig]

Re: Samsung Syncmaster 940BX backlight problem - Need help please.

Never mind

I see there on the aution now.

I couldn't find them on E Bay when I wanted one last year.