Samsung monitor won't turn on. (Syncmaster 941BW)

[Joe Black]

Re: Samsung monitor won't turn on. (Syncmaster 941BW)

And also, there is a darker spot on the board as well, but I'm not sure if it's a burn mark, or just a stain of some sort. Any ideas?

Many components get hot during normal operation, and heat will darken the board as in your case. Sometimes it indicates overheated component... My guess is those diodes are OK in your case. Of course, when in doubt, you have to test component to be sure. In this case, leave them be for now.

And, if you find that fuse is open circuit, resist the temptation to replace it and power on the monitor. Just report back here.

[momaka]

Re: Samsung monitor won't turn on. (Syncmaster 941BW)

I could potentially just take the power supply from the other (working) monitor, and put it in the bad one and test it out that way.

If you don't mind opening the other monitor(s), then that would be the best thing to do, since then you will know weather it is the power supply board or the main/video board in the monitor that is not working

Would it be a safe option, as long as I'm grounded properly, and (of course) very careful during the exchange?

Yes, it is safe both for you and the monitor. Just take these precautions:
1: Never disassemble or work on the monitor while it is plugged in (except for measuring voltages - in those cases, just avoid touching any metal parts on the monitor or the circuit boards).
2: Discharge yourself before touching the boards on the monitors with your hands (especially if you live in a dry climate area). This can be done by touching the metal case of the monitor.

how long should I have the power off before removing the (good) power supply?

That depends on the power supply design. The best practice is to unplug the monitor while it is either in the Standby mode (i.e. monitor LED lit with no signal going to it, like when the PC is off) or turned ON. In this case, the cap should discharge instantly.

On the bad power board, the high voltage electro cap could sometimes hold a charge indefinitely.

Either way, just avoid touching the "HOT" side on the board, and you should be fine. On the board markings, there is a thick white line, near the yellow transformer. It separates the power board into a "HOT" and "COLD" sides.

Now, as far as troubleshooting the possibly bad power board (should you find that the dead monitor is not working due to a bad power board)...
First watch this video to get more familiar with your multimeter (if you already aren't):
https://www.youtube.com/watch?v=bF3OyQ3HwfU

The next thing you will want to do is check the HOT side fuse and thermistor, as Joe Black suggested. No need to test the bridge rectifier yet (if it is blown, this will almost always cause the fuse to blow as well... so unless the fuse is blown, don't bother checking it). You can check these components while they are on the board (i.e. you don't have to remove them). The fuse is that round red cylinder, right behind where the power cable jack is. The thermistor is to the left of that (using your second attached picture as a reference) - it is green in color, and sits right next to that white-box capacitors (an X safety cap, to be exact). The thermistor is marked on the board as "TH01".

What you have to do to measure the fuse and the thermistor is set your multimeter to continuity (beep) mode and make sure that you get a audible beeping sound when you put the multimeter probes on the metal leads of those components (first check the fuse, then the thermistor). Alternatively, instead of using the continuity mode, you could also use the lowest resistance scale on your multimeter (usually 200 Ohms on manual-range meters) and see that both the fuse and the thermistor read less than 5 Ohms. Regardless of which way you do this, make sure the monitor is unplugged! The only time you will ever need the monitor plugged in while troubleshooting is if we ask you to measure DC voltages. For everything else, keep it unplugged.

Once you get these troubleshooting steps done, we will continue from there.

[CapLeaker]

Re: Samsung monitor won't turn on. (Syncmaster 941BW)

When the power supply is plugged in, be very careful on the primary "hot" side of the PSU. There are lethal voltages. For now I would avoid it, just do all the measurements in dc volt.

You can swap power supplies if the other one is the same or a sufficient alternate.

[TheCockroach]

Re: Samsung monitor won't turn on. (Syncmaster 941BW)

And ohh... speaking of actually.. one of my other monitors, is the same kind. I could potentially just take the power supply from the other (working) monitor, and put it in the bad one and test it out that way. Although, I'm also a bit hesitant to do it that way also, knowing my luck.

Would it be a safe option, as long as I'm grounded properly, and (of course) very careful during the exchange? I'm always extremely careful anyway, but I'm also unaware of how sensitive these components can be. And I guess another concern being, how long should I have the power off before removing the (good) power supply? Better to know, then to take a shock because the capacitor is still holding too much charge.

[TheCockroach]

Re: Samsung monitor won't turn on. (Syncmaster 941BW)

First you have to check if the PSU puts out STBY voltage 5V, which is always there. That goes to the main board. When you press the power button, the main board returns a PSon signal to the PSU and the PSU turns fully on.
Unfortunately I am not able to read the pin out on the PSU. Anyhow, this will get the ball rolling to determent what board is at fault.

I have someone bringing a multi-meter later, so hopefully I can find out then, thanks! Is there any good guides here for testing different components with one, though? I've only had to use a multi-meter a few times, and never on anything this complex. Just want to make sure I get it done right, obviously. I always like to be as knowledgeable as possible about things I'm trying to fix though, although I guess that's a good thing haha!

And also, there is a darker spot on the board as well, but I'm not sure if it's a burn mark, or just a stain of some sort. Any ideas?

Your monitor probably wont have V+ on the connector, and most likely main power board is down.

Take care all the time, that big cap can hurt. I am not sure if it has a bleeding resistor...
Maybe someone else will see it.

Check:
-Fuse (If blown should be replaced with 20-30W bulb in series for now, that's good practice for us beginners)
-NTC (Varistor)
-Both sides of graetz bridge for short (outer legs are output inner are input)
-Test graetz out of circuit
-Test switching transistor (U101 it seems)
-Good luck

Not exactly sure what ALL of that is, but I'll definitely find out, and test it all as well, thank you for the guidance! And also, where is the fuse at for the board? Is it what I'm pointing to in the below picture?

[Joe Black]

Re: Samsung monitor won't turn on. (Syncmaster 941BW)

Your monitor probably wont have V+ on the connector, and most likely main power board is down.

Take care all the time, that big cap can hurt. I am not sure if it has a bleeding resistor...
Maybe someone else will see it.

Check:
-Fuse (If blown should be replaced with 20-30W bulb in series for now, that's good practice for us beginners)
-NTC (Varistor)
-Both sides of graetz bridge for short (outer legs are output inner are input)
-Test graetz out of circuit
-Test switching transistor (U101 it seems)
-Good luck

[CapLeaker]

Re: Samsung monitor won't turn on. (Syncmaster 941BW)

First you have to check if the PSU puts out STBY voltage 5V, which is always there. That goes to the main board. When you press the power button, the main board returns a PSon signal to the PSU and the PSU turns fully on.
Unfortunately I am not able to read the pin out on the PSU. Anyhow, this will get the ball rolling to determent what board is at fault.

[TheCockroach]

Hello.

So, I woke up this morning, and my monitor won't turn on. This caused a horrible start to my day, as I had a lot of work to do. I use a three monitor set-up, but for what all I do, it's barely enough as it is, so having even one go out can be disastrous for me. I'll try and lay out exactly what happened, in hopes that someone is able to help me figure out if it's salvageable.

My PC is always running, but I turn my monitors off via the power button each night before bed (still plugged in though, of course), and then switch them back off when I get up. Well, I woke up this morning, and it seems my PC was actually OFF, so not sure what happened there.. But I'm fairly sure it wasn't a power outage, since my microwave time didn't get reset. So it was either shut-down by a windows update, or by a power surge in my room. (The monitor in question, WAS hooked up to a surge protector, though.)

So I went to turn my PC back on, and then hit the power button on each of my monitors. My far left monitor though, did NOT come back on. There is no indication of it receiving power whatsoever, and I've even tried different outlets. The power button doesn't flash at all, even when unplugging/plugging it back in.

Monitor: Samsung 941BW

I've taken it apart as well, just to check and see if a cap had went bad, but it "looks" as if they are all fine. I know kind of what to look for to know if one was bad, but I know sometimes you can't tell by just looks. Either way though, I thought I'd ask here since I'm not an expert on the topic. Just trying to figure out what went wrong, so I can order the part(s) needed to get it fixed. I've also included some pics of the board as well.

Please let me know if there is any other information that you need to know, in order to offer advice about this. Or if there is anything in particular that I can try. Thank you ahead of time, I will be checking back very frequently.