I had a Compaq/HP tc4200 with a dim screen after installing Windows 7. It was barely readable and causing considerable eyestrain. The function keys, that should have adjusted the brightness, did not work. I wondered if it was a issue with the graphics driver.

In addition, there is an issue with the ambient light sensor. In fact the two issues are very closely related, and could be entirely due to the ambient light sensor.

The Drivers

Confusingly, there are two distinct device drivers pages on the HP support website, with one page offering older drivers than the other.

From the HP Compaq tc4200 Tablet PC landing page, selecting XP 32 bit takes you to the HP Compaq tc4200 Tablet PC – XP 32 bit support page, under Driver – Graphics, one can download sp36236.exe, version 4631.FBC (18 Jun 2007), with a size of 5.2 MB. The contents of which is the Intel 915GM Video Driver (Intel 915GM Graphics Driver (American, International)).

However, on another page (HP Compaq tc4200 Tablet PC), different, older, drivers are provided:

  • For Vista 32 bit, Intel 915GM Graphics Driver for Microsoft Windows Vista, the file is sp34749.exe, from the HP tc4200 support page for Windows Vista 32-bit, version 4704, Jan 30, 2007, with a size of 8.4 MB.
  • For Wind0ws XP 32-bit, HP Notebook Display Driver, the file is sp29947.exe, version 3992 A, Mar 10, 2005, with a size of 6 MB.

Description of sp36236.exe

Intel 915GM Video Driver for Microsoft Windows XP

Hardware enabling driver for video graphics subsystem.

PURPOSE: Routine
SoftPaq NUMBER: SP36236

EFFECTIVE DATE: 18 June 2007
CATEGORY: Driver – Graphics


HP Compaq nc4200 Notebook PC
HP Compaq nc6110 Notebook PC
HP Compaq nc6120 Notebook PC
HP Compaq nc6220 Notebook PC
HP Compaq nc6230 Notebook PC
HP Compaq nx6110 Notebook PC
HP Compaq nx6120 Notebook PC
HP Compaq tc4200 Tablet PC

Microsoft Windows 2000
Microsoft Windows XP Home Edition
Microsoft Windows XP Professional
Microsoft Windows XP Tablet PC Edition


Resolves an issue where display could turn a single solid color after idling for varying amounts of time


1. Download the SoftPaq .EXE file to a directory on your hard drive.

2. Execute the downloaded file and follow the on-screen instructions.
Copyright (c) 2007 Hewlett-Packard Development Company, L.P.

I had installed this driver, along with the many others for my laptop after a reinstall of Windows 7. However, I found my screen going very dim and the brightness keys did not work.

After removing the Intel 915GM Video Driver from Programs and Features control panel, and rebooting the screen brightened considerably, and the brightness function keys (F9 and F10) began to work again.

Ambient Light Sensor

I found that even though the new graphics driver had improved the brightness and that the Function keys (F9 and F10) relating to the increase/decrease of the screen brightness, now worked, the screen was still rather dim, and that it was causing me eyestrain. However, I also noticed that the screen was considerably brighter during the day than at night time, when the lights were on. I, then, realised that there was an ambient light sensor positioned in the top left hand side of the screen surround.

[photo of light sensor]

If a light was shone into the light sensor then the screen became much brighter, to a comfortable and usable level.   It seemed to me that it would be a good idea to disable the light sensor.

I came across Ideas to hack NC4200 LCD ambient light sensor?

Some software for the asus EEE,  called EEECTL, can control the fan, CPU speed, and LCD brightness (on the EEE), and can be downloaded here: http://www.cpp.in/dev/eeectl/. Even though the software is intended for an ASUS, it can be used to control the brightness of a HP Compaq tc4200.

A hack of the software is available at http://pages.infinit.net/thief/Eeectl.zip. To quote:

Here’s the modified version of Eeectl that does not have the speed, fan and temp modules.

It allows you to control the brightness of your laptop LCD via software ! Note that you have to disable the ambient light sensor in order for it to work (it’s Fn+f11 on my model)


I have included the modified source code so you can take a look. I basically have commented the modules’ header and removed the corresponding .c and .h from the project.

The default configuration file (the .ini file) has the system tray icon display the current brightness in %, you can adjust the brightness using CTRL+UP and CTRL+DOWN. The program starts at 100%.

If you have any NCxxxx or TCxxxx laptop, I suggest you give it a try, you might have a display that is crippled at 75%.

I’m curious to see if it works on many laptops. Maybe just on intel video ?

I hope this thread helps somebody else that is looking for an answer regarding this issue.

 Normal operation

In theory, it should be possible to disable this ambient light sensor, assuming that the Quick Buttons software is installed, by using the F11 key – see Hp tablet compaq tc4200.The screen is very dark cannot adjust brightness in control panel. However, this software only appears to work with XP or Vista.
From the newer (see above) Drivers page, for Windows Vista Business 32 bit, looking at the Quick Launch Buttons software, under the Drivers – Keyboard, Mouse and Input devices (3) section, sp 38266.exe (28 Jan 2008). However, this is an older version, 6.30 J1, than I already have installed as I have 6.50 N1.As I downloaded 6.30 from the newer site, I am no sure where version 6.50 came from, unless it was automatically updated.

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