LCD Desktop Monitor Fading to White, then Black

Can you observe discrete jumps in the fade, ie stepped. Is it a backlight problem? if so perhaps find the brightness control line to the inverter and break there and add your own subcircuit perhaps. First monitor that line as maybe a fault inside the inverter chip

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Thanks for the quick response. I do not observe discrete jumps in the fading--it seems very smooth to me.

I do not know if it is a backlight problem; how can I tell?

I don't think it is a backlight issue My bet is a circuit problem with something common to all colors.

The brightness increases to max, then it goes negative to black. Then it pops back to normal.

A lot of monitors have everything wrapped up in one chip. Some ICs may drive the monitor directly.

Look for unstable supply voltage. If the voltage is going on/off abruptly but has a big cap on the line that would explain it.

on

A backlight gives general brightness to an image. if it is out, the video will still be there and u can see the image if u shine a light on the screen - effectively replacing the backlight.

your issue looks like the video is changing - not a backlight issue.

check the PS voltages first.

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The problem isn't occurring at the moment. When it returns, I will try shining a light at the screen to determine if the problem is the backlight.

Regarding the supply voltage: both monitors (as well as the computer itself) get their power from an APC UPS. When the problem returns, I will try using the outlet directly on the wall.

/watch?v=3DW7YpFZVRjcE

One thing I forgot to mention about the video is that it is not demonstrating the typical "end" of this problem.

Typically, the monitor fades to all white, then to all black (as captured in the video), and that's it; it will stay black. It typically does not cycle the way it does in the video, at least not indefinitely. It may cycle several times, but within 1 and ~5 cycles (usually just 1 cycle), it will stay in the "black" state.

What brand/model monitor? What brand/model card with NVidia chip?

Does the monitor have a DSUB I/O? Does the video card have a DSUB I/O

The symptoms don't describe an inverter problem to me but rather an LCD matrix drive, possibley PSU derived.

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Both monitors are a Samsung SyncMaster 204B. The video card is a ASUS EN7600GT.

The monitors have 1 DSUB I/O port and 1 VGA I/O port. I've only ever used the DSUB I/O. The video card has two DSUB I/O ports. Each one is connected to a monitor.

As I mentioned in the OP, when the monitor is malfunctioning, I have swapped the DVI cables between the monitors. When doing so, the malfunctioning monitor continues to malfunction while the other monitor (the one which has never malfunctioned) continues to function properly. So from this, I believe the computer & video card are functioning properly. Am I making a valid assessment here?

Is the PSU typically isolated from other circuitry in the monitor such that it can be replaced?

Does this monitor have buttons on the front to control brightness? Could one of those be stuck or shorted?

David

on

If it is the backlight, you can still see a picture in strong ambient light, try different viewing angles and light angles. If you can still sortof see a picture, it is the backlight. The slow fade suggests the invertor,or its powersupply circuit.

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I don't have any suggestions, but it is definitely Not the backlight. With a fading backlight the picture would just get darker and darker, there would be no video reversal such as shown in the video.

The problem indicates an problem with the video controller IN THE MONITOR. The Samsung 204s (and other Samsungs) have a bad reputation for this reason. A slow fade to white can be a problem with the power to the LCD panel itself, a fast fade to black can be caused by the inverter. A slow fade to black MUST originate from the video controler.

Open up the monitor, using all applicable precautions. On the video controller should be several three terminal devices, but labeled with a U number (as a hypothetical example, U404). Those are voltage regulators. It is remotely possible that one of those may be putting out an incorrect voltage. The last two digits in the part number will be the output voltage. Again, a hyprtetical part number - L117N33B is a 3.3 volt regulator.

PlainBill

Thank you for supplying the maker and model number.

This might be of interest:

I've seen both problems on the bench with similar Samsung models.

My usual method is to replace *ALL* the large value electrolytic capacitors. The labour is less to do it at one time, than to spend any time finding which one or two is the culprit. Make sure you buy

105C or 125C replacement caps as the 85c variety don't last. Larger values and voltage ratings are fine, but watch out for package sizes and lead spacing.

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As I mentioned in the OP, when the monitor is malfunctioning, I have swapped the DVI cables between the monitors. When doing so, the malfunctioning monitor continues to malfunction while the other monitor (the one which has never malfunctioned) continues to function properly. So from this, I believe the computer & video card are functioning properly. Am I making a valid assessment here?

Yes, of course -- that's Troubleshooting 101.

What's going on is that the video information is being lost, and the pixel "twist" is being forced all the way one way, then all the way the other way. As to the cause...

Are you connected to a Laptop ? is power saving kicking in an option available in your LCD if the battery is getting low? Maybe we went over that already, I'm too tired to look back.

I like the 'crazy LCD controller' idea -- bad connection somewhere making it cycle through the brightness range -- doesn't seem like faulty components could make an LCD smoothly cycle brightness how you describe?

So I think the culprit is the controller PCB in the LCD, unless bad power is provoking the thing to craziness?

Grant.

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http://bugs.id.au/

Agree with you, there's usually room to squeeze in higher voltage caps, and, with switching regs you could drop capacitance a little bit[1] and not harm the circuit performance -- ripple current rating of the caps is more important than the capacitance value of replacement cap.

[1] Got some 390/63 and 820/25 105'C low ESR caps I'd use instead of 470/35 and 1000/16 in a repair.

Grant.

--
http://bugs.id.au/

I was thinking capacitor too. In the old analog days one would searching for a leaky coupling cap in the video amplifiers :)

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It has buttons on the front, but not to control the brightness or contrast directly--those are available a couple levels deep in the menu. When the problem returns, I will try adjusting the brightness & contrast via the monitor to see what happens.