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Help with laptop external monitor no display

Discussion in 'Hardware' started by leegibsonuk, Jan 16, 2003.

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  1. leegibsonuk

    leegibsonuk Thread Starter

    Joined:
    Jan 16, 2003
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    This is a real tricky one, any help would be greatly appreciated.

    Basically the problem is:

    We have a laptop, which like many laptops has an external display connector (standard 15 pin D-SUB VGA) but also like many laptops looks for an external monitor & if it can't find one (presume via the sense lines) disables the external output.

    3 Modern flat panel displays I have tried work fine but 3 older CRT's do not (they come up initially when the computer boots then at a point it the startup when it does the check the external signal shuts off). I have to get it working with one of the CRT's.

    Yes, I can force it to output with keys function/F12 but it has to be an unattended feature during power cycling.

    In the cable can I short a combination os sense pins to mimic the newer screens so that the external VGA output is always on.

    I have tried shorting pin 11 (Sense ID 0) to ground and pins 4/11/12 (sense ID 0,1 and 2) simultaneously to ground but still the laptop does not detect the monitor.

    This should be really simple but it isn't I have spent hours and hours researching on the Net to no avail.

    Hope someone can help.

    Regards
    Lee Gibson
     
  2. dvk01

    dvk01 Moderator Malware Specialist

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    First Name:
    Derek
    You have got the refresh rate on the graphics card set too high.

    A flat panel display works at a different refresh rate to most crt monitors. set the refresh rate to between 60hz /72 hz when you want to use a crt display that should solve the problems

    Derek
     
  3. leegibsonuk

    leegibsonuk Thread Starter

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    Jan 16, 2003
    Messages:
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    Thanks for the info, tried it but didn't help. It is definately a line sense issue. I set the display settings to external vga out only (and then mirror mode for both laptop display and external) and on 'aaply' it did what it should (also same effect via function F12) but on reboot not only does the external monitor not stay on (it comes on initially unitl the point of detect, I amguessing) but on going back into settings the they have reverted to internal only mode.

    I think:

    It boots up, senses what it thinks is no external monitor, terminates the external RGB output and the updates the display setting to reflect the new hardware settings (ie reverts back to LCD2 the internal display).

    Regards
    Lee
     
  4. dvk01

    dvk01 Moderator Malware Specialist

    Joined:
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    Messages:
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    First Name:
    Derek
    Have you actually tried altering the refresh rates

    If the crt monitor is showing when first booting, then it must be detected by the computer. If it goes off after post, then that is when the graphics card takes over and all it's settings come into play.

    When the refresh rates are outside of what a crt monoitor can display it just shuts down and displays a black screen.

    You say that external flat panel/lcd screns work, that is because they use a vastly different refresh rate and crt monitors will only work with clearly defined refresh rates.

    the safest to try is to set the refresh rate to either 60 or 72 hz, all crt monitors will work at that setting as will any flat screen.

    other settings such as screen size and resolution are not important, it is purely the monitor refresh rate.

    Derek
     
  5. Jedi_Master

    Jedi_Master

    Joined:
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    Messages:
    5,520
    Howdy there dvk01...

    On some Laptops you can force the CRT mode via the BIOS...

    Have you tried that ?
     
  6. leegibsonuk

    leegibsonuk Thread Starter

    Joined:
    Jan 16, 2003
    Messages:
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    I fixed this problem today!

    The sense lines issue was a red herring, although all the symptoms did seem to fit this.

    Although it was not to do with monitor synch trying this did set me on the right track. I tried all the different output Vsynch settings (60 Hz etc) and it made no difference. I then went one step further and change the colours to 256 instead of high colour and, rebooted and guess what it worked! I then tried again in the reuqired hi colour (and true colour) and it still killed the output on restart.

    I knew the card supported both internal and external in hi colour because I could set it manually, sounded like a VGA driver bug to me. I found out that the integrated GFX chipset is an Sis 630 so looked for a driver update. One had just been posted and although in the fix list it didn't list my problem I gave it a try and the problem was solved. What a pian in the backside! In hindsight had it not been a laptop (with the known kill the output if no monitor attached red herring) it would have been a lot more obvious I think.

    Thanks for all your help.

    Cheers,
    Lee.
     
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