Problems with Samsung 740N monitors

[EGuevarae]

Re: Problems with Samsung 740N monitors

I loss confidence on Samsung LCD mainly due to the bad cap and poor design they used, not because the design can't withstand my try, and i did realise it would burn the whole thing if i short the fuse, I just want the quick solution to proof the back light is still functioning.

As a so called veteran in forum, be patient when u post any reply, in this case, you are overreact.

He's not a "so called veteran". He is not a moderator just because he did not want to due to reasons out of the scope of this thread.
The problem with Samsung,and with all other manufacturers is (most of the time) not in the design,but in the implementation of the design or the parts chosen.
And as for the "overreact", how would you call your solution,shorting a fuse with one known bad/burnt component,that (the fuse) blew up trying to avoid what you forced (burn another component by bypassing the fuse)? That's not the bad thing here....the bad thing here is that you are blaming Samsung for your reckless approach to a "quick solution"
And as a so called Newbie, you should show some respect to other members ....if they call you like you were called it was for a reason,not out of the blue ....

[coolkwc]

Re: Problems with Samsung 740N monitors

He's not a "so called veteran". He is not a moderator just because he did not want to due to reasons out of the scope of this thread.
The problem with Samsung,and with all other manufacturers is (most of the time) not in the design,but in the implementation of the design or the parts chosen.
And as for the "overreact", how would you call your solution,shorting a fuse with one known bad/burnt component,that (the fuse) blew up trying to avoid what you forced (burn another component by bypassing the fuse)? That's not the bad thing here....the bad thing here is that you are blaming Samsung for your reckless approach to a "quick solution"
And as a so called Newbie, you should show some respect to other members ....if they call you like you were called it was for a reason,not out of the blue ....

I mentioned in my previous post already, i blaming the Samsung because the used of bad cap. I lost confidence once i opened the panel and saw those bulge caps inside. Is the structure of my sentence to make you guys misunderstood, really sorry for my poor sentences.

Here i say one more time, i didn't blame Samsung because of my 'quick solution' approach. Foolishness and reckless if i don't know what will happened but blindly do it, in fact I know the risk when i did that so i felt offended by his words. This argument won't ever happen if there is no accuses from him at 1st place.

[EGuevarae]

Re: Problems with Samsung 740N monitors

...., in fact I know the risk when i did that so i felt offended by his words....

Sorry buddy, but that's why he said what he said : it's even worse if you did it knowing the consequential damage ... truth hurts sometimes.
But move on, stay on topic.
And you did not answer what caps did you install as replacements ...

[Hannes]

Re: Problems with Samsung 740N monitors

Hello all of you!!!

I have to thank you all... for your constructive input. Couple of weeks ago my Samsung SyncMaster 931BW did fall into permanent sleep. All tries to reinitiate it failed to work (slapping, kissing, pushing strange buttons no one ever pushed before...). For a strange reason I hated giving up on that one, because the moitor was running OK, since one day it was only Game Over... Now I thought try and open it up to see if there is a fuse broken (like in older TV´s there I thought there was a retractable fuse), but no. No retractable fuse. Now I got eager and tried to find some information on the internet.
Just one question: did someone already try that? It was confusing work for 2 days at least to sort out all the crap that is written over Samsung LCD TV, broken, warraties, on/off problems and so on but no solutions. Now in the end I found your Forum --> Finally!!! I was about to quit on it. Then in this Thread I found some pictures of the powerboard which led me to mine. My powerboard is kind of different to the 740-line but still it´s a very similar construction.The rest is history. I changed the capacitors (not all, only the 4 biggest and the 2 fuses (there is no picofuse anymore in my board). Only 2 red round ones. One with 3,15 and the other with 2,1. Now I have my monitor back running and the one I bought 3 month ago, so I get to run my PC on 2 now. I added to old one as an extention. I tested the monitor now for 3 days in a row and it works fine. Hope it stays this way and it doesn´t lead to changing even more strange things I read on my way to the end of this thread...
Just one last thing in the end: it is perfectly right that not all broken capacitors are bulged, mine looked ok, but 2 1000uF´s had gone looking "Braindead".
So good luck to you soldering your board back to present. If I could (I am a total newbie to this) you can too.
See ya


Daniel

PS: Don´t worry about my english I´m from germany (and had already a couple of beers right now).

[soft1]

Re: Problems with Samsung 740N monitors

Just a thank you to everyone that provided valuable information. Even if the posts were just asking for help, the problem descriptions were very useful to me!

After reading the thread three times (or thereabout), I managed to revive 14 Samsung LCDs. Here are the repairs in case someone else might find it useful:

• Samsung 940T (9 units) All of which have the 820uF 25V (3 pcs) replaced, and all have the 3A picofuse replaced (all blown). In addition, one of them also had the AF4502C MOSFETs destroyed--although the MOSFETs did not look burnt to my untrained eyes, pins 3 and 4 were shorted. It was my first SMD job and the monitor did not catch fire... There are evidence that the MOSFETs were generating a lot of heat as the clear plastic under backing on a couple of the boards were melted. Although on those two boards the MOSFETs were OK. Whereas the board with the destroyed MOSFETs, the plastic was not melted.
• Samsung 214T (4 units) All of which have the 820uF 25V (2 pcs I think) and 330uF 25V (3 pcs) replaced. I used 330uF 35V replacements because I could not get 330uF 25V caps in the same diameter.
• Samsung 940BX (1 unit) one 470uF 25V replaced (this cap is soldered on horizontally), and one 1000uF 16V cap replaced. I think there were one other 1000uF 16V and one 1000uF 25V caps that were not bulging. I replaced the 1000uF 16V with a 1000uF 25V. I did not replace the non-bulged caps.

That is all. I think I did OK for a mechanical engineer wielding a soldering iron. I hope this can be some encouragement to someone else. If anyone is interested, I took some pictures.

[jpxavier]

Re: Problems with Samsung 740N monitors

Samsung 740N: I replaced the 3 caps that were bulging. Waiting for the pico fuse to arrive. the one on the board looks okay. But not sure how to test for blown fuse. Anyways, the question when assembling back, I forgot how the two cables on the side are connected? the one pair with green at the top or otherway ? the pictures that I found on a service manual shows the bottom cable and top cable connected differently. But a picture on this forum shows both cables connected the same way.

[retiredcaps]

Re: Problems with Samsung 740N monitors

But not sure how to test for blown fuse.

Set your multimeter on the lowest ohms setting. Put your red probe on one side and black on the other.

With power off and lcd unplugged, a good fuse should measure less than 1.0 ohms on your multimeter.

[jpxavier]

Re: Problems with Samsung 740N monitors

Thanks retiredcaps for the quick response.
To add clarity to the second question of my post, I am referring to the first picture from this post #62: https://www.badcaps.net/forum/showpo...4&postcount=62
Look at the two (or four) cables on the left hand side. Both have the green cable at the top. One of the PDF that shows the disassemby had it differently.

[PlainBill]

Re: Problems with Samsung 740N monitors

Thanks retiredcaps for the quick response.
To add clarity to the second question of my post, I am referring to the first picture from this post #62: https://www.badcaps.net/forum/showpo...4&postcount=62
Look at the two (or four) cables on the left hand side. Both have the green cable at the top. One of the PDF that shows the disassemby had it differently.

In most cases it doesn't matter. In virtually all monitors the CCFLs are identical.

PlainBill

[bsweasel]

Re: Problems with Samsung 740N monitors

Thanks retiredcaps for the quick response.
To add clarity to the second question of my post, I am referring to the first picture from this post #62: https://www.badcaps.net/forum/showpo...4&postcount=62
Look at the two (or four) cables on the left hand side. Both have the green cable at the top. One of the PDF that shows the disassemby had it differently.

If your referring to the power cables that go to your CCFL backlights, it shouldn't matter. Each of the 4 lights have a positive and negative. Wether the pink or blue/green are on top or bottom is irrelevant from what I've seen, the polarity is inherent in the connectors. Someone correct me if I'm wrong.

[PlainBill]

Re: Problems with Samsung 740N monitors

If your referring to the power cables that go to your CCFL backlights, it shouldn't matter. Each of the 4 lights have a positive and negative. Wether the pink or blue/green are on top or bottom is irrelevant from what I've seen, the polarity is inherent in the connectors. Someone correct me if I'm wrong.

In the vast majority of cases you are right. It might be possible that someone has produced an LCD display with CCFLs of two (or more) different lengths, but I have never heard of one.

PlainBill

[jpxavier]

Re: Problems with Samsung 740N monitors

Awesome! What can I say.. After 3 820uf 25v caps, 1 3A pico fuse, monitor is back to life!! Thank you all...
Purchased all components from digi-key - Excellent place to shop.. all arrived within 2 days of placing the order.

[jpxavier]

Re: Problems with Samsung 740N monitors

In the vast majority of cases you are right. It might be possible that someone has produced an LCD display with CCFLs of two (or more) different lengths, but I have never heard of one.

PlainBill

BTW the order did not matter in my case: 740N. It worked either way..

[ivanlee05]

Re: Problems with Samsung 740N monitors

Hi.

Does anyone here has a copy of Samsung's IP-35135B power+inverter board schematic diagram? The one that included in the Samsung *40N/T service manual does not match the parts on the board. I badly needed this one. I'll be thankful if you can share it with me.

Thanks

[wanyf]

Re: Problems with Samsung 740N monitors

Guys, I just replaced the 820uF caps and the pico fuse and it works. Testing it 24hours now. Cheers.

[Kampfwurst]

Re: Problems with Samsung 740N monitors

Hello

I have a 2.5 year old Samsung 740B. The Backlight is not working. I replaced the 3 820uF capacitors but still nothing. Before it stoppt working the monitor was making a noise like a transformer station.

Is there anything what i can check. With the flashlight i can see the explorer but the backlight is still dark.

Christoph

[jetadm123]

Re: Problems with Samsung 740N monitors

Hello

I have a 2.5 year old Samsung 740B. The Backlight is not working. I replaced the 3 820uF capacitors but still nothing. Before it stoppt working the monitor was making a noise like a transformer station.

Is there anything what i can check. With the flashlight i can see the explorer but the backlight is still dark.

Christoph

You'll have to post some photos of your board so that members can see what you're seeing. Trained eyes may spot something that you overlooked. At this time, I would suggest checking the fuse of the 13V output. The 13V output powers the inverter section.

[Kampfwurst]

Re: Problems with Samsung 740N monitors

i copy the picture from another Thread



I replaece the 3 capacitor

where is this fuse. is it the brown one next to the power plug?

[alexanna]

Re: Problems with Samsung 740N monitors

The pictures are not the best in this thread, if you have a decent camera use it. you will get more help.
If your board is identical as the one in this thread look at post #25

[Kampfwurst]

Re: Problems with Samsung 740N monitors

i found the Fuse. The fuse is broken. ( 800 ohm ). Can i use a glas fuse??