Re: Problems with Samsung 740N monitors

Today I re-soldered all the remaining joints. Now when I did a cold start (after all the soldering)...the backlights remained on for an hour or so.

But again the flickering resumed. Although now i notice the flickering is less frequent.

Am attaching new pics of the solder side of the board.

Next I plan to physically check the lamps.

Please advise if any other checks need to be done to reach the core issue.

Thanks...

Re: Problems with Samsung 740N monitors

Hello Behemot,

The solder that i am using is TIn-Lead (60-40) composite. Hope thats good enough.

Have resumed now...will finish re-soldering the remaining joints and then post my board's pics.

Thanks...

Re: Problems with Samsung 740N monitors

Yes it was taken at different times....normally fluctuates 3-4V....for example during 1 reading 319V-323V...

Re: Problems with Samsung 740N monitors

@Behemot:

The drain voltage when the Lamps were on was shuttling between 11V-14V. Not sure if my multimeter was jumpy, or the voltage itself.

When I removed both the lamps completely, the voltage on 820uF remained steady at 13V.

Taking your advice I resoldered many points....especially since my monitor was manufactured in Feb 2006. The monitor turned on for atleast half hour without flickering. But soon the symptoms came again.

So am going to resolder, rest of the points and then give it...

Re: Problems with Samsung 740N monitors

Thanks Behemot for the speedy reply.

The solder joints are looking strange in the photos...due to the flash and resolution. Let me take a better picture in the daylight tomorrow.

With only 1 CCFL connected (either of them)...they were still blinking.

I will check again the voltage on the 820uF caps, without the CCFLs and post in my reply tomorrow.

By the transistors drain, do you mean drain pins on the 4502C? If yes please let know if the multimeter should be set on AC / DC ?
...

Re: Problems with Samsung 740N monitors

Hi there,

I have a Samsung 740N for which I had faced a problem with backlight in Dec2011. Changing the 820uF caps and the pico fuse had solved the problem them.

This time I have the same problem as described by many others in this thread. The backlight blinks (there is no pattern..and now it prefers to stay off longer).

Checked the secondary resistance of the inverters and found the resistance on both the windings to be 1338 ohms. I understand from a previous post that this is correct.
...

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...