Folks,
I am trying to figure out why this Dell shuts off the backlight in a few seconds (sometimes as long as 7 seconds if from a cold start).
Nothing seems to be blown or burnt. No swollen capacitors. No blown fuses. All voltages are present. All 7 CCFLs light up uniformly, no purple hue, no hissing noise from their terminals.
I have attached a file with pictures and a table of voltages on the boards.
Several things seem to be out of the ordinary.
1. The big electrolytic capacitor "C605" on the PSU shows 168v DC when the power LED is OFF. When I turn the monitor ON (power LED is ON) its voltage spikes to about 417v DC and immediately falls to around 292v DC.
I also measured the AC voltage across this cap. It shows 60mv AC when the power LED is OFF. When I turn the monitor ON its voltage rises to about 2.5v AC and in a few seconds (after the CCFLs go out) the voltage falls to around 164mv AC.
2. The "ON/OFF" voltage on the Inverter PCB is 0v DC when the power LED is OFF. When I turn the monitor ON its voltage rises to about 3.25v DC and in a few seconds (after the CCFLs go out) the voltage falls to around 0v DC.
3. The "DIM" voltage on the Inverter PCB is 0v DC when the power LED is OFF. When I turn the monitor ON its voltage rises to about 3.25v DC and in a few seconds (after the CCFLs go out) the voltage falls to around 2.87v DC.
4. The inverter controller OZ9966SN has a mystery chip resistor R015 next to it that shows open circuit. It is slightly larger than the other resistors and does not have any markings on the body except for two parallel thin lines looking like this: ||. Could it be a blown SMD fuse?
5. There is a mystery 2-pin connector (CN002) on the Inverter PCB that goes to the T-Con PCB (LTM240CS05FFCC4LV0.4). I don't know what it does.
Please share any thoughts that you might have. Thanks much!
I am trying to figure out why this Dell shuts off the backlight in a few seconds (sometimes as long as 7 seconds if from a cold start).
Nothing seems to be blown or burnt. No swollen capacitors. No blown fuses. All voltages are present. All 7 CCFLs light up uniformly, no purple hue, no hissing noise from their terminals.
I have attached a file with pictures and a table of voltages on the boards.
Several things seem to be out of the ordinary.
1. The big electrolytic capacitor "C605" on the PSU shows 168v DC when the power LED is OFF. When I turn the monitor ON (power LED is ON) its voltage spikes to about 417v DC and immediately falls to around 292v DC.
I also measured the AC voltage across this cap. It shows 60mv AC when the power LED is OFF. When I turn the monitor ON its voltage rises to about 2.5v AC and in a few seconds (after the CCFLs go out) the voltage falls to around 164mv AC.
2. The "ON/OFF" voltage on the Inverter PCB is 0v DC when the power LED is OFF. When I turn the monitor ON its voltage rises to about 3.25v DC and in a few seconds (after the CCFLs go out) the voltage falls to around 0v DC.
3. The "DIM" voltage on the Inverter PCB is 0v DC when the power LED is OFF. When I turn the monitor ON its voltage rises to about 3.25v DC and in a few seconds (after the CCFLs go out) the voltage falls to around 2.87v DC.
4. The inverter controller OZ9966SN has a mystery chip resistor R015 next to it that shows open circuit. It is slightly larger than the other resistors and does not have any markings on the body except for two parallel thin lines looking like this: ||. Could it be a blown SMD fuse?
5. There is a mystery 2-pin connector (CN002) on the Inverter PCB that goes to the T-Con PCB (LTM240CS05FFCC4LV0.4). I don't know what it does.
Please share any thoughts that you might have. Thanks much!
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