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Reg Hack/INF Fix: LCD Backlight fix


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Original Topic Desc: Gets the backlight to turn on/off when the lid is opened/closed

EDIT: I thought I had this fixed. I will try again and see if I can get it to resolve but I was sure it was working properly. I tried it recently and found that the backlight would not come back on without a restart so I dropped both keys for now. I'd rather it not work at all rather than only partially work.

EDIT (1/7/08): I'm going to give this another go real quick by adding back all of those keys from the post as well as my stuff. I will see if that restores functionality again and then try to reduce it down later.

The following keys are likely to affect the behavior: LidBehavior, ModesetBlankDelay, UseSingleSurfaceSemaphore, EnablePersistenceStorage, WidePanelBehavior, UseCVTReducedBlanking, dynEngCtrlEnabled

I know that LidBehavior will be required to make it work at all. This key alone is missing from the inf file.

EDIT *again*: I just checked it again. Same result now. Even with all of those keys. Something changed in my computer that caused this fix to break as I had it working fine before I made this post. Otherwise I wouldn't of gone all that I did. The below information will remain as information use only. I cannot support it anymore and it isn't endorsed by LV2G. Basically the result here is that the backlight will go off but will not turn back on. There is either a key that needs changed or added that is not in my original information.

Anything below this point is part of the original post information. The original slated "fix" that I thought would work. Anything above this point is additional information that I have added on since.

This is for those of you that are having this issue.

Ever since I started using any of the 1xx.xx drivers I noticed that the lcd backlight did not turn on and off when I opened and closed the lid. This is the automatic one that someone posted the infamous fix where you change LidBehavior to 11 and it took care of the issue on older drivers. With the newer ones this did not work. Adding LidBehavior allowed it to turn off and restored behavior as it would of been on 84.69 except that simply changing it to 10 did not resolve it. Upon changing it to 10 then the lid would close but only a restart got the backlight back on. This did show that the drivers support this functionality and now it was to find the other missing keys. Through alot of research I managed to find out which key was missing beyond LidBehavior and restore this functionality 100%. In addition dual screen support appears to be working properly although there may be some oddities. If you find any issues then let me know.

WARNING: These steps include instructions that require editing the registry. It is highly recommended that you backup the registry before proceeding.

NOTE: This fix is only tested on a Dell Inspirion E1705 with a Nvidia GeForce Go 7900 GS running Windows XP. Driver version 169.28.

Step 1: Open Registry Editor (obviously -- this is a reg hack)

Step 2: Navigate to the following location -- replace <CLSID> with the one for your card (I only had one):


Step 3: Add a DWORD key labeled LidBehavior and set it to 11

Step 4: Add a DWORD key labeled EnablePersistenceStorage and set it to 1

Step 5: Reboot and test!

Please note that you can have this fix integrated into the inf by adding these lines under [Mobile_Tweaks]

;Fix Lid Behavior
HKR,, EnablePersistenceStorage, %REG_DWORD%, 1
HKR,, LidBehavior, %REG_DWORD%, 0x11

Unfortunately due to the fact that the clsid may vary from system to system I could not create an easy registry patch for this one. You have to add them to the registry yourself following the instructions, insert the above lines into your driver inf file or use the attached nv4_disp.inf file. The inf file is for driver version 169.28 only!


This post --> http://forums.laptopvideo2go.com/index....post&p=1772

It pointed me to the 6 keys that were not already in the registry. I added them and found it fixed the issue. The actual keys that did fix it 100% were found via trial and error. I attached my hack log that I wrote while doing it so you can see what I had done. You can see what I had done to find this.

Known Issues:

Dual screen mode may not be restored properly when you re-open the lid. On mine it is not. In addition the second screen takes over as primary (an expected effect) but then it goes to clone mode rather than going to dual screen mode. It may be due to the UltraMon Program I am using. I will reboot without it and retest. Updates to follow...

EDIT: If you have UltraMon installed then it seems to cause an issue with this. Probably a driver / application interaction issue.



Edited by shinji257
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