Samsung P2770HD Monitor; Brightness Setting Goes to Max after 10 - 15 Minutes

[whirligig]

This Samsung Monitor/TV is used as a computer monitor. Lately I've been dimming the brightness every so often but it will lose the setting and go max brightness. Now, after dimming the monitor, it goes to full brightness in about 10 minutes. When it is dimmed, I can hear a soft tone or buzz but when it goes to full brightness it's quiet. I suspect the chopper circuit for the CFL power supply is going. Hopefully, it's just a bad cap. What do you think?

Well, I checked my post from 3 years ago on Badcaps.net about another problem with this monitor where I replaced the step up transformer for the backlight. These monitors were not built to last. Well, I'll see what I can find when I open her up.

[samnmax]

Is it changing the brightness setting by itself, are you seeing the OSD brightness bar going to 100% on its own? I ask because I've seen this problem of phantom button presses on Benq and Samsung monitors before. The button switches go slightly conductive when not pressed (~5kOhm) and this is enough to trigger button presses because they cheaped out and used a single ADC line with multiple buttons to form a resistive divider.
However, I think your monitor uses capacitive buttons, in which case this will not apply, but they could also be giving phantom presses somehow.

[whirligig]

Yes, it will snap back to maximum brightness by itself. I will then dim it down and minutes later, it will brighten up by itself. The OSD will show 100% at max brightness. Hmmm, I'll see if this uses capacitive buttons or a resistive voltage divider.

I was thinking a bad cap in a PWM circuit that's chopping the voltage, but this should be easy to check.