Problems with Samsung 740N monitors

[selldoor]

Re: Problems with Samsung 740N monitors

We really need pictures of your boards - both sides - the one you have posted
tells us little of your problem and cannot be effectively enlarged.
The 12v is less regulated than the 5v and if the lamps are not lighting the voltage would rise a little.

Do the lamps flash at all

[agun82]

Re: Problems with Samsung 740N monitors

Hi guys,

I'm new here, so nice to meet you all.
I'm facing problems for 740N as well:

1) Power Led is not on at all, even if I push the power button several times.
2) I changed all three 820uf bulged caps with 1000uf/25v, and changed the 3A pico fuse (broken) , but the power led still not on.
3) I already changed the TL431, power led still not on.
4) All rectifiers are ok.
5) 3.15 fuse is ok
6) I have checked all CCFL with CCFL testers, all lamps light normally.
7) Although the power led is not on, but when I measure the voltage of the output pins (as shown in the pic below, circled.. I borrowed photos from kharr)
the readings are 5,1V and 14,8V. I know this should be 13V. Does 14,8V normal?




Any help please? Thanks a lot.

[j00j4nt200]

Re: Problems with Samsung 740N monitors

Thanks to this thread I managed to fix my Samsung 940b

There was a noise when blue led is blinking on standby and monitor wasn't waking up.
- first I changed 3 820uF/25V caps - no results.
- visual check - everything look ok.
- checked 2 AF4502C mosfets - ok
- checked t3.15a fuse - ok
- checked small fuse - ok
- checked some diodes - ok
- changed 3 1000uF/10V caps - Monitor is Working, I hope it will stay that way

[Behemot]

Re: Problems with Samsung 740N monitors

You can check the transformer easily: set ohm meter to 2K and measure both secondary windings. Both should be within few % of each other. If one is much lower or much higher, it is bad and you'll have to replace the whole transformer.

[Rtech]

Re: Problems with Samsung 740N monitors

LuSID....your transformer is the same as the one we are referring to.HOWEVER you have not said what fault symptom you have ???/the other problem with your board can be caused by failure of one or more of the 4 Big black diodes.

[LuSiD]

Re: Problems with Samsung 740N monitors

Hey guys,

Am i the only one that has this powerboard in my Samsung 740N?

See the attached pictures. The caps seem fine and are labeled 'JH'. What should I do? Does anyone knows what this board is and if it has the same problems with the common ones?

Thank you

Anyone?

Hey above posters. Did you reply to me or someone else?

[budm]

Re: Problems with Samsung 740N monitors

I agree with Rtech, check the resistance reading of the high voltage windings of the inverter transformer.

[Rtech]

Re: Problems with Samsung 740N monitors

The TMS Inverter transformers do fail,you need to check the secondary resistance of them

[LuSiD]

Re: Problems with Samsung 740N monitors

Hey guys,

Am i the only one that has this powerboard in my Samsung 740N?

See the attached pictures. The caps seem fine and are labeled 'JH'. What should I do? Does anyone knows what this board is and if it has the same problems with the common ones?

Thank you

[Behemot]

Re: Problems with Samsung 740N monitors

I'd take KY again, last time I checked, they've been somewhat cheaper than other series (LXZ, LXY). They also seem to have highest capacity in every particular diameter with 20 mm height.

[bowlofpudding]

Re: Problems with Samsung 740N monitors

before i order, anyone have any opinion on the chemi-con lxy series?

[bowlofpudding]

Re: Problems with Samsung 740N monitors

just got the 25mm height caps today, test fit them and theyre too big by like 2mm. they hit the top of the cage. probably shouldve done my homework before i ordered. so i guess ill be looking for the same caps but at 20mm height

[bowlofpudding]

Re: Problems with Samsung 740N monitors

the ones i ordered were 565-1553-ND from digikey. chemi-con KY series 25mm height (hopefully theyre not too big) i figured they would be a suitable replacement, since the ones were a bit bulged on top i figured wouldnt hurt to replace them, i would at least like to get a little more life outta this monitor even though i bought it used, and for cheap.

[Pentium4]

Re: Problems with Samsung 740N monitors

Hmmm....I forgot the other bad series....c_hegge would know

[Behemot]

Re: Problems with Samsung 740N monitors

KM is good series, mostly used as big high-voltage caps (often on primary side of PSUs or dispalys).

[Pentium4]

Re: Problems with Samsung 740N monitors

Or maybe it's KM...I've never actually seen them in person, just bad ones on the net

[Behemot]

Re: Problems with Samsung 740N monitors

Oh yeah, GK, too, booth green and very similar, I usually take them as the same Not familiar with KF though…

[Pentium4]

Re: Problems with Samsung 740N monitors

Most likely Samxon GF, their only bad series I am aware of. Replace on sight. Samxon GT is good substitute. Other than that, I source Chemi-Con KY's from Digi-Key with 20 mm height.

I believe KM and GK aren't very reliable either, if I remember correctly

[Behemot]

Re: Problems with Samsung 740N monitors

Most likely Samxon GF, their only bad series I am aware of. Replace on sight. Samxon GT is good substitute. Other than that, I source Chemi-Con KY's from Digi-Key with 20 mm height.

[bowlofpudding]

Re: Problems with Samsung 740N monitors

this is a pretty old thread but thought i would add to it. i have a syncmaster 930b, with the same board that everyones having capacitor troubles with (ip-35135b). the monitor made a buzzing noise, the backlight dimmed and i just got around to taking it apart to take a look. on the board the 2 8-pin mosfets going to the inverter transformer looked like they had a tiny hole burned through the center. when the monitor died it let out the fried electronics smell but since i waited so long to look at the problem the smell was long gone. i just ordered a new set of mosfets and am waiting for them to arrive and hope that fixes the problem. after reading all these posts im surprised the caps weren't swollen. the 820uf caps are samxon branded and the 1000uf caps are capxon branded. im starting to think i should preemptively replace them. im also curious why the mofsets just burned up in the first place, these things shouldnt burn up if the circuit was properly designed. i tested the resistance on the transformers and the readings on both were nearly identical. anyway thought i would share my experiences here since this forum gave me some insights

oh and i only find 1 fuse on the board labeled f101, cylinder shaped orange thing in line with the ac plug. i looked where everyone says the pico fuse is and i never found it. everything else on the board seems to be working fine though, i still see an image on the screen when i hold a light up to it. would be strange if they didnt include a fuse on this board but might explain why the mosfets blew

and 1 last edit. i just looked more closely at the 820uf samxon caps and the top isnt flat, its kinda of pushed out a little so im thinking it will be a good idea to replace these