My latest project is a Dell Studio One 1909, it's a 19" all-in-one computer/monitor. The problem is when you turn it on the screen comes up for about 5 seconds and then goes black. If you connect an external monitor the system works fine, so I know the problem isn't the computer side of things. If I shine a flashlight into the screen after it goes black I can still see the image. So the problem is the CCFL backlights.
Taking the back off I first looked at all the caps, especially those on the power supply and inverter boards (less concerned with the caps on the computer motherboard). All caps test fine on my ESR meter. The inverter board is a small board with a 6-pin connector to the motherboard. The pins aren't labeled, but I ran tests and figured each out.
1 and 2 - Both have a solid 12.1 volts during operation.
3 and 4 - Both ground.
5 - When you first turn it on the volts are 0, then after a few seconds it goes up to 3.2 volts and remains steady. I suspect this is the signal from he motherboard to turn on the backlights.
6 - When you first turn it on the volts are 1.6, then after a few seconds it goes up to 3.3 and remains steady. I suspect this is the backlight brightness level.
Since the signals from the motherboard to the inverter look right, I'm pretty sure the problem is either the inverter or the CCFLs. I'm looking for ideas on how to test/diagnose this further. I have two similar sized CCFLs salvaged from another monitor. The connectors are different, but if I adjust the connectors to fit can I just plug those in and try it? I've never swapped CCFLs between monitors before, so I don't know if this will work.
I fear the problem is the CCFLs. When the backlights are on, there is a slight buzzing noise from the monitor.
Attached a picture of the inside of the computer, as well as close-up shots of the inverter.
Taking the back off I first looked at all the caps, especially those on the power supply and inverter boards (less concerned with the caps on the computer motherboard). All caps test fine on my ESR meter. The inverter board is a small board with a 6-pin connector to the motherboard. The pins aren't labeled, but I ran tests and figured each out.
1 and 2 - Both have a solid 12.1 volts during operation.
3 and 4 - Both ground.
5 - When you first turn it on the volts are 0, then after a few seconds it goes up to 3.2 volts and remains steady. I suspect this is the signal from he motherboard to turn on the backlights.
6 - When you first turn it on the volts are 1.6, then after a few seconds it goes up to 3.3 and remains steady. I suspect this is the backlight brightness level.
Since the signals from the motherboard to the inverter look right, I'm pretty sure the problem is either the inverter or the CCFLs. I'm looking for ideas on how to test/diagnose this further. I have two similar sized CCFLs salvaged from another monitor. The connectors are different, but if I adjust the connectors to fit can I just plug those in and try it? I've never swapped CCFLs between monitors before, so I don't know if this will work.
I fear the problem is the CCFLs. When the backlights are on, there is a slight buzzing noise from the monitor.
Attached a picture of the inside of the computer, as well as close-up shots of the inverter.
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