Problems with Samsung 740N monitors

[selldoor]

Re: Problems with Samsung 740N monitors

Hi, Welcome to the forum
Does the power light stay on when the backlight goes off?
If so you probably have 2 seconds to black and should read this guide by retiredcaps - start at post 19.
https://www.badcaps.net/forum/showthread.php?t=10419
As you say it is not likely to be the fuse.

We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246

Do you have a multimeter

16v instead of 10v caps is ok

[moondoggie]

Re: Problems with Samsung 740N monitors

Hello all,
stumbled upon this thread and forum while fixing a 740N for a friend.

As usual opening it showed 2 cap's 1000uf 10VDC blown up. Changed them just now, and the monitor turns on to stanby. Glad i fixed it, i put it to my pc to test it for a few hours.
than i saw what i didnt see at first. the monitor lights up, and after 2 secs kills the lams. the picture works but dark. i shut the monitor off, turn it back on, same thing happens.

i'm going to open it again tonight, and search for that blasted 3A fuse i didnt know about, BUT... if the fuse isnt working, should the light come on for 2 secs than shut down?

any ideas on whats going on ?

ty in advance
md

p.s. i'll be scrolling thru these 15 pages slowly today, to see if i find my answer, so if its there soz for asking

p.p.s. the capacitors that i put on are 1000uF 16V instead of 10V

[mufti_GT]

Re: Problems with Samsung 740N monitors

Hi, lightning on my Samsung 940B stopped working, but thanks to this thread I managed to find and fix the problem. It was the usual stuff, the three 820uF 25V caps were bulged on top and the PICO 3A fuse was blown. I replaced caps with 2x 1000uF 25V and 1x 470uF 25V Teapo SY low ERS caps. I replaced fuse with a new one. The monitor works fine now.

Thanks again to creators of this thread

[Drools]

Re: Problems with Samsung 740N monitors

Thanks, I should have looked at CN2 more closely.
Interesting, I only have 1 cap that is on the +13 trace while 3 caps were on the +5 trace, yet I have 2 caps at 25VDC. They must have used a 25VDC cap on the 5VDC trace.

[retiredcaps]

Re: Problems with Samsung 740N monitors

oops, they are not all 470uf there were 2 x 1000uf 10VDC that were identical in size as the 470uf ones however I removed the caps so where did the 2 x 1000uf caps belong?

1) Take your multimeter and set it to continuity mode.

2) Put one lead on the connector CN2 where it says 13V.

3) Put the other lead on the positive leg of the capacitor hole. If it beeps, that is where the 25V caps go.

4) Put one lead on the connector CN2 where it says 5.1V.

5) Put the other lead on the positive leg of the capacitor hole. If it beeps, that is where the 10V caps go.

[Drools]

Re: Problems with Samsung 740N monitors

I pulled a bone-head move!
I have 2 x 940b 19" LCD monitors with badcaps in both. I'm experienced with electronics and replacing caps but I pulled a stupid.
My power board is the exact same as the one pictured in post #4 of this thread.
PN: BN44-00128A, I have seen it called Rev2.
I identified the caps needed or so I thought, 470uf at 25vdc times 5....
oops, they are not all 470uf there were 2 x 1000uf 10VDC that were identical in size as the 470uf ones however I removed the caps so where did the 2 x 1000uf caps belong?
Interesting enough, on the first monitor I did not catch my goof and replaced all the bad caps with 560uf @ 35VDC and the monitor works fine. I will fix my stupidity when I can identify the proper location for the caps in question.
C242
C235
C263
C241

C319 is a 470@25vdc as it was a different color so I remembered where it went.

Thanks for the help.

[indrair3]

Re: Problems with Samsung 740N monitors

Ok - you are not going to get much help by bumping a post.
You would get more help if you didnt post pictures in line and if the front of the board picture was the other way up so the numbers could be read.
A quick look through this thread doesnt show a board like this one and I have tried to find the board but failed - didnt spend a lot of time as I cant really read the model no.
Please state the model number and revision of the board and get a magnifing glass and post any numbers off the burnt component that you can decipher.

This the model number of the board :
--------
! level3 !
! LR76377 !
--------
-----------------------------------
! MODEL :PWI1904SJ(A)(B)(C) Rev 1.0 !
! INPUT :100-240V ~50-60Hz.1.0A !
! OUTPUTPN201) +5.1V---2.0A !
! +15.0V---0.3A !
! (PN1.PN2.PN4) = 650V~7.5mA !
-----------------------------------
YB751904SJ(A)005251

[budm]

Re: Problems with Samsung 740N monitors

More likely to be low Ohm (18, if those are the colors) since it will be impoosible to have high enough voltage on the board to generate enough current through 1000M ohms to burn it up.

[Behemot]

Re: Problems with Samsung 740N monitors

I have it but the restistor is totaly burned and reads as wire :-D I have replied in the thread of his…

[selldoor]

Re: Problems with Samsung 740N monitors

Better Idea - PM Bocca and ask him he has the same board and is working on it now.

[selldoor]

Re: Problems with Samsung 740N monitors

@behomot
Hi - have you taken it out - can you see the colours on the underside?
What does it measure?

Here is another board http://obrazki.elektroda.net/58_1284496626.jpg

Is that Brown Grey Black Gold - 18ohms 5%

Or Brown Black grey silver 1000M ohms 10%

[Behemot]

Re: Problems with Samsung 740N monitors

Here it is again as an attachement.

Anyone has the board shown in my earlier post (#304)? What is the R316 value please?

[selldoor]

Re: Problems with Samsung 740N monitors

Having enhanced your pic I think it might be one of these
http://ndft.com.ua/sites/default/fil...ic/stu407d.jpg

[budm]

Re: Problems with Samsung 740N monitors

@INDRAIR3:
Service manual:
http://elektrotanya.com/?q=showresul...oria=&kat2=all
That DUAL MOSFETs are badly burnt out, you need to look at the service manual for the P/N first. The IC (on the bottom side of the board) that drives the MOSFETs may be damaged also.

[Behemot]

Re: Problems with Samsung 740N monitors

This board does not look very good to say. It seems there is no fuse at all, thats usually the reas for half of the components to burn. Also thre are ordinary diodes instead of bridge rectifiers.

Anyway, to me, the component looks more like manual (re)soldered/changed to me. Is that some kind of dual transistor in one package?

[selldoor]

Re: Problems with Samsung 740N monitors

Ok - you are not going to get much help by bumping a post.
You would get more help if you didnt post pictures in line and if the front of the board picture was the other way up so the numbers could be read.
A quick look through this thread doesnt show a board like this one and I have tried to find the board but failed - didnt spend a lot of time as I cant really read the model no.
Please state the model number and revision of the board and get a magnifing glass and post any numbers off the burnt component that you can decipher.

[indrair3]

Re: Problems with Samsung 740N monitors

Dear all.
I have 740N and totally dead, led off dan smell something burn before it's dead. Before dead my 740N can be displayed but need about 5-10 minutes. I cek, one component, i don't know what it's melt, i can identified the series because the mark is missing, anyone knows what the cmponent it's?.
I'm also already change the 3 cap (1000uf/16v) and 1 470uf/25v, but it's not working. and where is the 3A pico fuse found? am i must change this fuse too??

Thanks for help.

up..up.. help please

[indrair]

Re: Problems with Samsung 740N monitors

Dear all.
I have 740N and totally dead, led off dan smell something burn before it's dead. Before dead my 740N can be displayed but need about 5-10 minutes. I cek, one component, i don't know what it's melt, i can identified the series because the mark is missing, anyone knows what the cmponent it's?.
I'm also already change the 3 cap (1000uf/16v) and 1 470uf/25v, but it's not working. and where is the 3A pico fuse found? am i must change this fuse too??

Thanks for help.

[jetadm123]

Re: Problems with Samsung 740N monitors

I have an 740N with a IP-35155A board. After switching the screen on the backlight is on for about two seconds and then goes off. The screen itself is still displaying, i can see it with a flashlight.
I replaced all capacitors which didn't help. The board has both transformators in one shell instead of two separate ones. The resistance on output side between 1 and 2 is about 1kohm, between 3 and 4 about 7.5kohm. So i think the transformer is faulty. On the upperside it has printed TM-1017, on the downside SEM1852. Where can i get a drop-in replacement for this transformer? I'm in europe.
Thanks.

TM-1017 is readily available on Ebay.

[sowi]

Re: Problems with Samsung 740N monitors

I have an 740N with a IP-35155A board. After switching the screen on the backlight is on for about two seconds and then goes off. The screen itself is still displaying, i can see it with a flashlight.
I replaced all capacitors which didn't help. The board has both transformators in one shell instead of two separate ones. The resistance on output side between 1 and 2 is about 1kohm, between 3 and 4 about 7.5kohm. So i think the transformer is faulty. On the upperside it has printed TM-1017, on the downside SEM1852. Where can i get a drop-in replacement for this transformer? I'm in europe.
Thanks.