Samsung 940BW won't turn on

[delturcious]

A number of months back my Samsung 19" widescreen stopped working after a lightning strike. I haven't had the time to mess with it until now, but I'd really like to get it working again. I'm no expert at component level repair (nor surface mount soldering) and at this point I'd be happy just to narrow the problem down to the controller or the power board. Components on the power board are large enough that I could probably replace them myself, but if the controller is fried, then I'll just have to replace it.

Neither board has any visibly-damaged components, but they never do, do they? The fuse on the power board still has continuity but I can't find one on the controller... maybe I'm not looking hard enough. At least some of the caps on the power board are charging. I'm not reading a voltage between the ground and any other pins on the harness that goes between the 2 boards.

The front control panel connects into the logic board. Is there a way to fool the power board into powering up the inverters and backlights? Pins on the harness between the boards are labeled B-Dim, +13V, GND, +5.1V, A-Dim, and O/F. Any ideas would be greatly appreciated

Decent-sized photos attached, but if you want the REALLY big ones, they're linked below... I figured 4MB each was too big to embed.

http://delturcious.net/samsung/IMG_1044.JPG
http://delturcious.net/samsung/IMG_1047.JPG

[Scenic]

Re: Samsung 940BW won't turn on

are you getting any voltage (DC) on the main filter cap?
that's the huge one.
be careful though, as it holds (or should hold) roughly 1.4 times the line voltage (around 170V DC for 120V and around 320V for 230V countries)

if not, the bridge rectifier (flat black box next to the huge main filter cap) might have failed.
the MOV (green disc in the bottom left of the PSU pic) looks like it's intact. they usually explode pretty violently or burn up if something goes wrong with them.

[delturcious]

Re: Samsung 940BW won't turn on

are you getting any voltage (DC) on the main filter cap?
that's the huge one.

Yup, getting ~165-170V according to my $3 multimeter and the MOV is intact

[Rtech]

Re: Samsung 940BW won't turn on

You can plug the Power Supply into the mains,plug in the backlights,and apply approx 3volts minimum(from a battery perhaps),between theO/F pin (positive) and GRound(neg).If all is well then the Lights should come on.

[retiredcaps]

Re: Samsung 940BW won't turn on

I'm not reading a voltage between the ground and any other pins on the harness that goes between the 2 boards.

If you are not getting secondary voltage as per above, the SMPS hasn't started. It could be the small cap around the SMPS is bad or the SMPS controller is bad.

1) What is the DC voltage across the small electrolytic capacitor just above JP104? Is it stable or fluctuating?

2) What brand and series is this cap?

3) What is the uF and voltage rating on the cap?

I figured 4MB each was too big to embed.

I'm especially grateful.

[stray77]

Re: Samsung 940BW won't turn on

Well I don't know if this will help or not but my Samsung SyncMaster 940BW died during storm as well. My solution was pretty simple though as C30 and C205 were obviously blown. They were C30(25V 470uf, CapXon) and C205(16V 1000uf, SAMWHA). Simply replacing these 2 capacitors was all it took for me.

[retiredcaps]

Re: Samsung 940BW won't turn on

They were C30(25V 470uf, CapXon) and C205(16V 1000uf, SAMWHA).

Capxon has a poor reputation with forum members here. The standard recommendation is to replace all the electrolytic capacitors, except the largest one which rarely fails, with quality low ESR ones like

https://www.badcaps.net/forum/showthread.php?t=2280

[tombshot]

Re: Samsung 940BW won't turn on

hello everyone, just want to ask if there is a schematic diagram of this samsung 940bw? (because i, too, also own one). I would like to learn it somehow....

My lcd 940bw problem is that when my pc is turned on, the monitor wont start... it takes too long for it to show visuals (before it ony takes 5-30 minutes, but seems like getting worse coz it took hours 5-12 hours before before it shows visuals...

Ive been told that inverter is the problem and some caps... but i dont know exactly where it shows...

highly appreciate for all your assistance....

(my first post here in BadCAPS.net :-))

[retiredcaps]

Re: Samsung 940BW won't turn on

Ive been told that inverter is the problem and some caps... but i dont know exactly where it shows...

Your symptoms sounds like bad caps. As the lcd gets warm, the ESR (ohms) of the caps decrease. When the lcd is off for a while, the cap's ESR is high and doesn't allow the lcd to turn on.

Take it apart and see the picture in post #6 showing bad caps. We do, however, want to see pictures of YOUR lcd.

PS. Capacitors die from age, heat, and shoddy build quality. Capacitors DO NOT have to be visibly bloated in order to bad. They can be out of tolerance uF (a 1000uF measures 20uF) and/or have high ESR (ohm). A multimeter will be insufficient to test for ESR. For that you need an ESR tester which costs between $50 and $300.

Most members here will recommend that you replace ALL capacitors with reputable brands from reputable sellers. Brands like Rubycon, Panasonic, and United Chemicon are suggested. A list of recommended caps can be found at

https://www.badcaps.net/forum/showthread.php?t=2280