Samsung 245bw flickering

[COASTER19]

Hi all! I have a Samsung Syncmaster 245bw which has the common flickering/horizontal lines problem. I've gone through the forums and found many threads on this monitor, most similarly to my problem this one.

Here's the whole story:

Before starting, The monitor partially worked, backlight present and flickery lines across the image. When I opened it up I saw that CB809 and CB876 were bulging, so I replaced them (along with the also known to fail CB872) with FM caps. I also tested the 68 ohm resistors which commonly fail on this monitor, and all were fine. When I reassembled it, the monitor wouldn't turn on at all. No lights anywhere. The 5v rail for PS_ON reads ~3v, but switches between that and 2.5v more or less at random, so something is clearly wrong leading to there. Furthermore, connecting it to PS_ON doesn't turn the other rails on as it's supposed to, but I think the problem is happening at some point before that.

Here's where this gets odd: I replaced the FM caps with the old bulging caps, and it partially worked again with the flickery image, but an image nonetheless. I thought I may have had some bad FM caps, so I replaced them again with new ones, but that wasn't the case, as I'm back at ~3v. The revision of the board I have doesn't have much of that partially conductive glue that some have, but I removed some of the glue on the board anyway as I wanted to eliminate that possibility.

Where do I go from here? I don't understand why the blown cap produces an almost working result but the new one doesn't produce the correct output at all.

Thanks in advance!

[COASTER19]

Re: Samsung 245bw flickering

I've been retracing the circuit using the attached PDF diagram, and found RB801 open circuit. I replaced it, but still no signs of life with the new capacitors.

[1supertech]

Re: Samsung 245bw flickering

Hello coaster do you have an ESR meter if not replace all caps and resistors RB807,RB805,RB806

[COASTER19]

Re: Samsung 245bw flickering

I've measured RB807, RB 805, and RB806, but all read 68 ohm as they're supposed to (and when measured in circuit read 200 ohms so they're all properly connected in series as per schematic)

I don't have an access to an ESR meter this summer, but should really just buy one at this point. Either way, I replaced all the caps I've seen other people have trouble with on here apart from CM802, as that's harder to find but also unlikely a problem as it's not in circuit with anything leading to the SB_5V rail.

I've probed lots of points and sometimes the rail does get the correct 5v output without any load, but then stops for a few seconds at 2.5 before going back to 5 every once and a while. When attached to the control board this period of 5v is so short my multimeter doesn't detect it, constantly reading somewhere from 2.5-3 volts. Therefore, I think it's somehow a problem with a component that's only appearing when current is being drawn.

More concerningly, I noticed that pin 7 of icb801S doesn't read any voltage despite it being the IC's vcc pin, so something before that likely causing this problem, but as far as I can tell it's all fine before there. I've not probed anything on the side of the transformer with BB801 and BB802 because mains, but I'm a little concerned that the transformer is somehow dead at this point. I don't understand how that makes it so it partially works with the bad caps installed, but I don't know what else to look for at this point. Suggestions?

[budm]

Re: Samsung 245bw flickering

So did you remove all the glues?
Did you replace capacitors CB806, 808, 810, 872?

[COASTER19]

Re: Samsung 245bw flickering

Fixed!

I had replaced CB872 at the time of the last post since it has been a problem for others. CB806 and 808 had no bulging (they're the type with vented tops where it would probably be partially visible), and since I didn't have any replacements on hand I left them. I didn't, however think to replace CB810. It's a 1uF 50v cap, and I have those on hand. Replaced it and all works great! Thanks!


Tl;dr - add CB810 to the list of parts that fail in this monitor.

[budm]

Re: Samsung 245bw flickering

Bad cap can look normal with no sign of bulging, glad to hear you get it fixed but I would still replace the rest of those caps the list I gave on post 5.