Member Avatar for ggeoff

Hi

I have managed to establish that my Dell laptop 6400 does not have a problem with generating display data. Connecting an external monitor provides a perfect picture. There is data going to the LCD screen but it is very dark. A web search suggests that I replace the inverter. I have done that but still have the problem. I have checked to see whether the new inverter was connected up properly and it is. I have run Dell Diagnostics and there is an error: "2000-0322 Error accessing the LCD inverter" On reflection, I should have run the diagnostics before buying a new inverter!

Whilst checking to see whether I had pushed the connecters to the new inverter fully home I managed to get the display working, but I lost it again. This suggests to me that the new inverter is working ok and maybe the old one was as well! I also checked the connections behind the LCD display, they are OK. So I am now thinking of what I need to do to check whether the power supply to the inverter is stable.

If my reasoning is correct what do I need to do to check the power supply to the inverter? But also, is there some other factor that clouds the issue?

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Dani AI

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Quick practical summary and what to try next. A dark internal LCD with a perfect external display usually means the image data is fine and the fault lies in the backlight power chain (inverter, backlight tube, or the wiring/connector that feeds them). As eventually discovered here, an intermittently loose video/backlight connector is a very common cause and will produce exactly the on/off behaviour you described. 's suggestion to try the brightness keys is a good quick check, but you still need to follow the hardware checks below before buying parts.

  • Confirm it is a backlight problem: boot to BIOS or POST and shine a bright flashlight close to the screen. If you can faintly see the desktop/menus, the LCD is receiving video but the backlight is not lighting.
  • Try brightness controls in BIOS and OS (quick, low-risk test). If the screen never brightens, move to hardware checks.
  • Inspect and reseat connectors. Remove the bezel carefully, reseat the inverter-to-panel plug and the inverter-to-board power/logic plug, and inspect the cable where it passes the hinge for broken wires. Intermittent contact here is the most common fault and matches 's final finding.
  • Check the inverter low-voltage input with a DMM (DC): power the laptop, set the meter to DC, and confirm there is DC present on the small power/logic connector when the display should be lit. If the LV input has no DC, the inverter will not run even if it is new.
  • Do not try to measure the inverter high-voltage AC output to the CCFL with a standard DMM. That output is high-voltage and often high-frequency; DMMs (including many Fluke handhelds) will not measure it correctly and it is dangerous without the correct HV probe or oscilloscope and safety precautions.

Safety and prevention: disconnect battery and AC before connector work, use antistatic precautions, and secure the cable after repair (small piece of tape or a strain relief) so the thick cable cannot pull out again. If reseating and confirming DC present does not fix it, either the inverter or the CCFL/backlight is defective — swap with a known-good part or seek professional repair.

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Member Avatar for dee101g

You could be having an invertor problem, but have you tried looking for the key that has a blue circle with an arrow pointing up and clicking it a couple times while holding down the Fn key? That's what mine needed when it gave the symptoms you are recounting.

Member Avatar for ggeoff

Thanks dmcaarison,
"You could be having an invertor problem, but have you tried looking for the key that has a blue circle with an arrow pointing up and clicking it a couple times while holding down the Fn key? That's what mine needed when it gave the symptoms you are recounting."

Yes, I have used the screen brightness keys. I have seen though, that when the screen is dark, the brightness menu is missing. The Error message provided by Dell Diagnostics also refers to the inverter.

Member Avatar for ggeoff

Hi

I have managed to establish that my Dell laptop 6400 does not have a problem with generating display data. Connecting an external monitor provides a perfect picture. There is data going to the LCD screen but it is very dark. A web search suggests that I replace the inverter. I have done that but still have the problem. I have checked to see whether the new inverter was connected up properly and it is. I have run Dell Diagnostics and there is an error: "2000-0322 Error accessing the LCD inverter" On reflection, I should have run the diagnostics before buying a new inverter!

Whilst checking to see whether I had pushed the connecters to the new inverter fully home I managed to get the display working, but I lost it again. This suggests to me that the new inverter is working ok and maybe the old one was as well! I also checked the connections behind the LCD display, they are OK. So I am now thinking of what I need to do to check whether the power supply to the inverter is stable.

If my reasoning is correct what do I need to do to check the power supply to the inverter? But also, is there some other factor that clouds the issue?

My reasoning is correct, the video cable plug had come disconnected. This was most likely to be caused because the cable is quite thick and could exert enough force to loosen the plug. I might also, which is quite likely, have moved the video cable when I replaced the inverter.

Incidentally, I couldn't manage to use my Fluke 110 multimeter to take a Hz measurement, as mentioned by Morris Rosenthal of Foner booksto, to check whether an inverter is working or not. If I can find out why, maybe my DMM is defective, I'll post back as that technique could be usefull for a lot of PC users, whether they are Dell owners of laptops or not.

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