Syncmaster 740N PSU problem

[Hallucin]

Hi, I have a problem-have monitor Samsung 740N..I first noticed the buzz from the monitor. After research on the internet have changed the 5 capacitors (marks on the picture) worked 2 hours normally and then the picture disappeared. (power led stay on) When you turn off and restart the monitor, for a few seconds so the images begin to lose contact and then goes out. and so always.when the screen turns off to reduce the buzz. these days, the monitor is turned off so only when it is half lit ... you have any idea what to substitute for the power supply? I have noticed that the heat capacitors and transformers ...

here is picture and video link. any help or same problem? Thanks in advance

image:

caps: 2x 1000uF/25V and one 1000uF/35V (in line)
bottom: 2x1000uF/16V

video:
http://www.box.net/shared/dnqpyii5oq

[seanc]

Re: Syncmaster 740N PSU problem

What replacement capacitors did you install?
They need to be low ESR.

[Hallucin]

Re: Syncmaster 740N PSU problem



35V is jamicon, others are "NA" :S
I doubt that is the reason, because until I changed the capacitors are known quenched but only if the monitor stayed lit half a day... Oo

[Bobdee]

Re: Syncmaster 740N PSU problem

Looking at that video link, indicated to me possible faulty CCFLs due to the pinkish looking screen

[Hallucin]

Re: Syncmaster 740N PSU problem

no, screen colors are okay, my mobile camera su*ks, that is the reason for pinkish looking screen.

[Hallucin]

Re: Syncmaster 740N PSU problem

gosh: S I noticed that the backlight turns off after only a few seconds, I see the picture when direct light close ... I am totally confused now: (

[Hallucin]

Re: Syncmaster 740N PSU problem

when the brightness decreases, surprisingly it works Although little is heard some noise. When i enhance brightness buzz noise becomes louder and louder and then back lights goes off after a few seconds. Even I'm starting to suspect that the sound coming from the transformer and that with him something was wrong .... has anyone any advice what to try to replace?

[seanc]

Re: Syncmaster 740N PSU problem

Change all caps for low ESR caps.
Jamicon are general purpose. Who knows what those 'NA' are.

[sofTest]

Re: Syncmaster 740N PSU problem

Agree with seanc, symptoms is typical for high ESR caps (even new).

[Hallucin]

Re: Syncmaster 740N PSU problem

I'll try to find here, I'll probably have to order because it is in Croatia all electronics completely "Made in China" -.-'. again, I doubt that it is up to it. Please note, the monitor had the same symptoms before changing the capacitors even though none of it seemed suspiciously. Thanks for your answers.

[EGuevarae]

Re: Syncmaster 740N PSU problem

I'll try to find here, I'll probably have to order because it is in Croatia all electronics completely "Made in China" -.-'. again, I doubt that it is up to it. Please note, the monitor had the same symptoms before changing the capacitors even though none of it seemed suspiciously. Thanks for your answers.

Caps can look OK and yet have problems, like in this case, more ESR than needed, either because failure (original ones) or not being the proper specs or GP (Replacements).
You can not troubleshoot unless you are sure caps are OK. That's what I do, at least ...

[Hallucin]

Re: Syncmaster 740N PSU problem

I ordered new capacitors and still waiting to arrive. Currently there are jamicon capacitors that I put another a week ago. Today I tested a bit, I first tried to turn on the monitor with the lower light (I exclude upper) and after 3 seconds lamp turned off the immediately (I guess this is some protection as a sign that I need to include both) I also tried it with the same upper and same happened. After that, I'm going to try both again and now works smooth like new. still do not know what was the problem? Is it important? xD I hope that the lamps will not turn off once again after one hour.