Faulty Screens. Flickering to black. Syncmaster 940be and 940ux

[tungsten]

I have a 940BE and a 940UX that when turned on will very lightly flicker for a couple seconds then go black. I can view the screen with a flashlight, and the led power light stays on.

I also have a 940BE and 940UX that have this exact same problem, but after turning them off then on around a dozen times they will finally turn on and stay on for hours.

It's the screen part (see pic "screen") that is faulty. Because when the faulty "screen" is paired with known to be working boards, it has the same problem. But when I pair the boards from the faulty monitor, with a known to be working "screen" it works just fine.

Is the green board on the back of the screen in my screen picture the inverter board? Is this most likely where to problem lies? Any information would be very much appreciated. Also I can supply any pictures if needed.

Thank you!

[Rtech]

Re: Faulty Screens. Flickering to black. Syncmaster 940be and 940ux

Its probably the Lamps themselves and/or their assoiated wiring that is causing the probems

[tungsten]

Re: Faulty Screens. Flickering to black. Syncmaster 940be and 940ux

Its probably the Lamps themselves and/or their assoiated wiring that is causing the probems

I appreciate it. In the attached picture I disconnect what I assumed to be half of the lamps, and turned it on with the exact same outcome. I also reconnected those two wires, and unplugged the other two. Does this get me any closer to the problem, or am I completely wrong wrong about those wires? Also is the green board in the pic the inverter board, or is the inverter board under the metal casing?

Thanks!

[tungsten]

Re: Faulty Screens. Flickering to black. Syncmaster 940be and 940ux

I forgot to add the picture.

[tungsten]

Re: Faulty Screens. Flickering to black. Syncmaster 940be and 940ux

I'm so sorry. I was having troubles uploading, and I could not find a way to delete posts, or edit a post to add a picture.

My apologies.

[re-atari]

Re: Faulty Screens. Flickering to black. Syncmaster 940be and 940ux

I appreciate it. In the attached picture I disconnect what I assumed to be half of the lamps, and turned it on with the exact same outcome. I also reconnected those two wires, and unplugged the other two. Does this get me any closer to the problem, or am I completely wrong wrong about those wires? Also is the green board in the pic the inverter board, or is the inverter board under the metal casing?

The inverter board is the one you connect the pink and light blue wires to. This board contains the power supply as well. The wires lead to the lamps, 2 on top and 2 on the bottom of the screen assembly. They carry high voltage (about 800V), so be careful when handling them. You need to connect all of the pink and light blue wires for the screen to switch and stay on, otherwise the inverter's protection circuitry will kick in.

The board under the metal shield on the topside of the back of your screen is the T-con board. Be careful with this one, the brown plastic 'flatcables' on top of this board are glued onto the PCB and the panel. If they get damaged your screen is de facto a total loss. If that's the case the screen will display discolored vertical lines.

For starters you could try bringing the first 2 monitors back to life by replacing the caps on the inverter board. They are relatively inexpensive (compared to replacing the lamps), and it will reduce the number of possible causes for your fault. The second 2 monitors appear to suffer from caps that are well underway to their grave. Replace them before they do so and possibly take out other components as collateral damage.

Post some hires/close-up photo's of the component side of the inverter/PSU board to show the state the caps are in. A shot cap is not always visibly damaged, though, but the opposite (bulging caps) is a clear indication that they need to be replaced ASAP. Rtech's advice as suggested in post #2 (faulty lamps or wiring) is a good one to check out while you're at it.

re-atari

[tungsten]

Re: Faulty Screens. Flickering to black. Syncmaster 940be and 940ux

Thanks for all the great information! I opened up the two monitors that only work for a second, and found that the CCFLs were broke on the top of each. I was able to salvage the bottom assembly on one and reverse it and use it as a top assembly on the other!

About the monitors that go out after a couple hours. Since I am able to swap out the two boards with good working boards and the same problem happens, that rules out the caps right?

Thanks!

[tungsten]

Re: Faulty Screens. Flickering to black. Syncmaster 940be and 940ux

Ok, now the monitor I just fixed by replacing the CCFLs is getting super hot. I can even smell the heat. Is there any chance something on the boards is overheating and may have caused the CCFL to crack?

[re-atari]

Re: Faulty Screens. Flickering to black. Syncmaster 940be and 940ux

Ok, now the monitor I just fixed by replacing the CCFLs is getting super hot. I can even smell the heat. Is there any chance something on the boards is overheating and may have caused the CCFL to crack?

That doesn't sound good, I bet it doesn't smell OK either
I think it's wise to investigate what's causing this before something (your monitor, room, house) gets a chance to go up in flames.
Speaking from experience: I have a PSU board from a 931BW laying around, where 2 8-pin mosfets literally burned themselves up and in doing so burned a hole straight through the PCB! The fuse intended to protect this circuitry was still intact, naturellement
I'm glad this happened when the monitor was still in the hands of the previous owner.

An inverter with one or more caps that have developed high ESR over time, and/or CCFL's that have reached the end of their life, will put a lot of strain on the inverter circuitry that was certainly not calculated in when it was designed. It will run hot as a result. You need to find out which component(s) get this hot, and then deduct what's causing it. I'd take a good look at the caps, and just replace them all the same. Easier and cheaper than replacing those flimsy CCFL's. If those are gone, their inside will be blackened on one or both ends. You should be able to spot that on your monitor, the left and right side of your screen will then be lit considerably less.

I'd start with fixing the second 2 monitors and make sure they work flawlessly. That will give you a reliable platform for swapping boards or CCFL's when fixing the other 2.

re-atari

[re-atari]

Re: Faulty Screens. Flickering to black. Syncmaster 940be and 940ux

About the monitors that go out after a couple hours. Since I am able to swap out the two boards with good working boards and the same problem happens, that rules out the caps right?

That would indeed seem to rule out the PCB as the culprit, unless it shuts down after a few hours because of overheating. I'd still take a good look at the caps on the inverter, if only to eliminate them as the cause of all your trouble.

re-atari