Hi guys! I’m using a Philips CRT monitor. When I was working on the computer, all of sudden the monitor brightness got changed and now the screen is too bright. The brightness can’t be control with the front side controller!! However the screen contrast can be changed! . After I got this problem, I saw a very bright light appears in the middle of the screen when the monitor is power off. ( just like a camera flash light) .; can you suggest what can be the problem ?



Monitor : Philips 104E

 

The monitor symmetric diagram is attached herewith. (http://www.4shared.com/document/cErzPYPO/Monitor_Philips_104S.htm)

 

When 'off' do you mean when unplugged or when the image is blank?

I suspect the HV voltage is higher than it should be. But HV should not be present (except as charge in the tube) when the monitor is unplugged.

 

When the monitor is turn off by power on switch

 

When unplugged does it exhibit the same symptoms? Can you take a picture?

 

I can adjust my monitors brightness, contrast, gamma, blah, blah, blah, from the "control panel" of my display options.

You may be able to also.

I would try unplugging the monitor to try and reset any custom changes. Some monitors do not save setting over an unplug.

 

It is NOT a problem with the HV.

Sounds like it has a problem in the CRT blanking circuit &/or beam current control circuit. When you turn a monitor off it's supposed to blank out the drive to the electron guns and there's a number of ways they went about doing that.

Sadly there's more ways to build monitors than you could count and the only way to properly service them is to have a proper schematic and a bench set up to service these type things - even then many weren't designed to be easily serviceable to begin with.

For now about the only temporary solution would be to look on the back for a G2 control, if it isn't there it would be inside, usually on the back of the flyback transformer but sometimes on the CRT PC Board. You can adjust the overall beam current down with this control at the expense of losing a bit of linearity in dark to bright response.

If you don't have experience in servicing TVs or monitors I'd step lightly, they can hold all sorts of voltages (even aside from the HV) long after they've been powered down. The actual metal chassis can be "floating hot" too so I wouldn't touch it while plugged in - operating or not.