Problems with Samsung 740N monitors

[Haktar]

Re: Problems with Samsung 740N monitors

Thanks to all the info on this tread i've managed to bring a new lease of life to an old IBM think vision monitor, turns out the 3 caps where bad, and also the fuse needed replacing happy days!

[SirDuck]

Re: Problems with Samsung 740N monitors

Sorry for raising a dead thread guys :/ I need some quick help, i have the same problem with the caps and the fuse, but I can't find the same fuse in any store in my town. Would a glass 3A fuse do instead? I am aware that this may be a dumb question, but I'm somewhat a newbie to electronics, and i don't want to mess thing up since I have no money for a new screen :/

Thanks in advance

[PlainBill]

Re: Problems with Samsung 740N monitors

Sorry for raising a dead thread guys :/ I need some quick help, i have the same problem with the caps and the fuse, but I can't find the same fuse in any store in my town. Would a glass 3A fuse do instead? I am aware that this may be a dumb question, but I'm somewhat a newbie to electronics, and i don't want to mess thing up since I have no money for a new screen :/

Thanks in advance

Both Mouser and Digikey are also good sources for fuses. This application requires low ESR caps which you won't find in Radio Shack.

PlainBill

[SirDuck]

Re: Problems with Samsung 740N monitors

Both Mouser and Digikey are also good sources for fuses. This application requires low ESR caps which you won't find in Radio Shack.

PlainBill

I don't live in USA, nor can I order from any of these shops. I asked if the pico fuse and the glass fuse are the same thing from the perspective of making this circuit work, not where can I buy fuses in the US

I also don't live in Germany or any other country Mouser branches out. So, the question stands, can i use a glass fuse instead?

[pedro]

Re: Problems with Samsung 740N monitors

I don't live in USA, nor can I order from any of these shops. I asked if the pico fuse and the glass fuse are the same thing from the perspective of making this circuit work, not where can I buy fuses in the US

I also don't live in Germany or any other country Mouser branches out. So, the question stands, can i use a glass fuse instead?

<rant>You really would help people to help you if your profile indicated where you are.</rant>

[SirDuck]

Re: Problems with Samsung 740N monitors

<rant>You really would help people to help you if your profile indicated where you are.</rant>

Belgrade, Serbia, how does that help you answer a theoretical question?
I don't want to find the pico fuse, I want to use a glass fuse. Can that be done?



They are also easier to replace if this thing happens again.

[PlainBill]

Re: Problems with Samsung 740N monitors

Belgrade, Serbia, how does that help you answer a theoretical question?
I don't want to find the pico fuse, I want to use a glass fuse. Can that be done?


They are also easier to replace if this thing happens again.

Theoretically any fuse with identical speed and current ratings and the same or greater voltage rating can be used provided it fits into the available space. In a practical sense, any fuse is better than using a jumper wire. From a professional point of view, using a 3AG fuse to replace a picofuse is a sign of an amateur, and I wonder what other shortcuts may have been taken.

PlainBill

[alexanna]

Re: Problems with Samsung 740N monitors

Belgrade, Serbia, how does that help you answer a theoretical question?
I don't want to find the pico fuse, I want to use a glass fuse. Can that be done?



They are also easier to replace if this thing happens again.

From past experience, it's always best to replace the fuse with the exact same spec.
On a really nice 24” monitor I replaced a 4 amp fast blow fuse with a regular 4 amp blade fuse.
The outcome wasn't pretty, I had a Mosfet explode and it did damage to the inverter Circuitry was damaged beyond repair.
So whatever you do, be careful the outcome may not be what want.

[SirDuck]

Re: Problems with Samsung 740N monitors

@alexanna, than you, I will see where can I get a pico fuse from. That info was all I needed

@PlainBill, bravo *clap clap*, you sure proved to me how smart you are. And also professional.

[jetadm123]

Re: Problems with Samsung 740N monitors

@alexanna, than you, I will see where can I get a pico fuse from. That info was all I needed

@PlainBill, bravo *clap clap*, you sure proved to me how smart you are. And also professional.

You can always try Ebay for pico fuses.

[SirDuck]

Re: Problems with Samsung 740N monitors

You can always try Ebay for pico fuses.

I've found them in my country in another city, but they don't have the 3A fast right now, so I'll just wait, it will be lot cheaper than e-bay. Thanks for the advice thou

[Randomish]

Re: Problems with Samsung 740N monitors

Greetings, one and all. My first post, and I would have edited my personal details but the User CP function doesn't seem to be enabled for me yet.

Regardless, I work in MA for a large company, and we've got scores of Samsung 740N failing now, after 42 months of use. At least, that's an estimate, as most were manufactured in April of 2008. All but one case I've come across was a simple matter of replacing the obviously burst capacitors, the classic 3 820uf 25v. I always want to improve my skills, so I'm redoubling my efforts on the one board I haven't been able to fix.

Having replaced the capacitors, I put the board back, fired it up, and I have a blinking blue light for normal standby mode. When I add signal, the light turns to a solid blue, but I still have no display. Pressing the OST button yields no menu. Having just learned about the picofuse from previous posts, I did test it with some ohm leak while still soldered (compared to 0.0 when checking the other fuses), and after I removed it, it didn't zero out using the digital multimeter. I ordered a 5 pack from ebay for $6 which I should see Wednesday. if there is another part I should be checking during the wait, please feel free to let me know.

That being said, I've seen plenty of people refer to the 18v bridge, or the 5v, etc, and I have no clue what that's about, as I have yet to successfully download the service manual for the IP-35135B using any of the links I've seen posted by other members. Once I have that in hand, I plan to look up how to actually USE a multimeter, and I would appreciate any suggestions on links for newbies in that regard.

Incidentally, ALL of the other boards I have seen are of a different model than this one- I distinctly remember not seeing the scores of resistors between the CCFL leads on those models.

[retiredcaps]

Re: Problems with Samsung 740N monitors

Once I have that in hand, I plan to look up how to actually USE a multimeter, and I would appreciate any suggestions on links for newbies in that regard.

http://www.youtube.com/watch?v=bF3OyQ3HwfU

[guestxx]

Re: Problems with Samsung 740N monitors

I wanna thank you all for helping me also. Changed the caps. it wasn't working, saw this thread, it showed me the position of the fuse, replaced it and it works again! 740B

[tom66]

Re: Problems with Samsung 740N monitors

If so, why does a company like Samsung use caps from a known bad supplier? Maybe this doesn't surprise you guys but it is going to turn out to be a big warranty issue for Samsung. It seems that a company of their size would not slip up like this. Your thoughts on this subject are welcome.

From what I have seen of Samsung, I do not like it. Samsung don't want their products to last, why would they? You're unlikely to upgrade your LCD monitor every 2 years so making it fail every 2 years is an easy way to get people to buy more monitors. Otherwise they wouldn't make as much money. Products aren't designed to last, unfortunately.

We are steps away from seeing software lockouts or deliberate bugs being introduced into firmware (like leap year bugs... *cough* PS3 *cough* ... at least they fixed it) which stops boards working after a number of hours (Epson printers stop printing after a number of pages have been printed, because they think the ink sponge is clogged up, and you can only reset it by hacking the firmware.)

[raokd]

Re: Problems with Samsung 740N monitors

Hello, I am from India and was really frustrated, when after coming back from a weekend outing, my monitor (Samsung 740N) refused to show the images even though the power led turned on.

Thanks to all the experts on this forum and the pictures posted by other members, could find out the swollen caps. Didnt suspect the fuse though, till I replaced the caps (with 25V 820uF) and the monitor still would not show anything except for the power led lighting up. Finally replaced the fuse as well.

Thanks once again to all the message writers on this forum.

[Behemot]

Re: Problems with Samsung 740N monitors

I got two 940B together with 240B, all three have the same symptoms.

The 240B and one 940B work after complete recap and fuse change, second 940B has image but no backlight. When I tried to measure output voltage on invertor there is 0. My multimeter reads only up to 600 V but still it should at least show "1", no? Already swapped displays so the problem is in the inverter itself, not in CCFLs.

It has fine 13 V input, I can read 5 V on the small cap on inverter side (swapped for Nichicon HE 33 uF/35 V). Fuse did not blown again. May the transformers or driving circuitry be bad?

ADD// Outputs of both inverter transformers read some 950 ohms on resistance test. Transformer input reads 33,5 V AC when turned on. I expect the inverter transformers are bad if there is input on primary but nothign on secondary, right?

I have similar looking transformers from one LG where probably data board was bad. Do you think I can use them here?

[retiredcaps]

Re: Problems with Samsung 740N monitors

It has fine 13 V input, I can read 5 V on the small cap on inverter side (swapped for Nichicon HE 33 uF/35 V). Fuse did not blown again. May the transformers or driving circuitry be bad?

Post a picture of your boards.

Check any mosfets in the inverter section for shorts.

[Behemot]

Re: Problems with Samsung 740N monitors

Same board as in posts #12 and #17. If U need higher res, I will be taking photos of motherboard for review tomorrow, can photo this too.

I found no shorts so far. Anyway, if there were some, I would probably not get fine 33,5 V input into the inverter transformer, isn't that so?

[pedro]

Re: Problems with Samsung 740N monitors

I got two 940B together with 240B, all three have the same symptoms.

As these are NOT 740N's, it would have been better to start these as a separate thread so that others with those models would have more chance of finding this discussion.