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Old 06-27-2005, 09:50 AM   #1
hpladd
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LCD monitor works in Debian not Redhat


I have a dual boot machine: Debian -- kernel 2.4.27-2-386 and Red Hat -- kernel 2.4.20-8.

I recently acquired a LCD monitor and it works great when running Debian, but I receive a "Cannot Display This Video Mode" warning when trying to run X in Red Hat.

Interestingly, both the Red Hat and Debian xf86config files are still configured to work with the CRT monitor that was in place during the original install. In fact, I don't know why the LCD monitor works in either setup?

I'm assuming the Debian kernal has a module compiled into it that recognizes the LCD monitor and the Red Hat kernel does not.

I'm almost as interested in knowing why the Debian setup works as I am in knowing how to get the Red Hat to function.

Thanks All
 
Old 06-27-2005, 11:03 AM   #2
TheGiantPotato
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LCD under RedHat

To tell you more about hwy, I need to know which version of RedHat are Debian you are using. Providing the kernel numbers is great, but it doesn't tell me about the rest of the system.

It could be that your Debian is more recent than your RedHat. Nowdays the consumer version of RedHat is Fedora Core, as it accordingly comes with a glut of drivers and perifpheral recognition routines not ever seen in a RedHat release to date. For this reason, Fedora Core 4 recognised my hp mx70 monitor as exactly an hp mx70 (which totally shocked me), while RedHat 9 always called it a "generic XXXxXXX crt".

I had no problem displaying to an Envision lcd monitor with RedHat 9 on my other system, but it was not automatically recognized by its type. It was identified as a "generic lcd". I had to enter the refresh rate, resolution, etc. manually to confiure it to operate propely, and it took a little fine-tuning to make it display every graphic mode properly. I did, however get it to work eventually.

I suspect that your version of Debian is a little more modern than your version of RedHat, and can cope according to what hardware its recognizing.

Two questions: when you boot RedHat, do you at least get the basic text output as it starts up? Does GRUB or LILO display properly prior to booting one or the other? If the answer is "yes" to both of these, then your problem is nothing more than the parameters being fed to X. This would confirm my suspicion that your version of Debian is merely coping for bad parameters being fed to X, and RedHat is not. Fedora should, I believe.
 
Old 06-27-2005, 11:10 AM   #3
MasterCephus
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I am running Fedora and I was using a CRT Samsung monitor. Then I bought an LCD monitor and I kept getting errors that would say that the resolution wasn't right and would keep just turning off. Once I went in and changed it to the right monitor in the config file for X, it worked perfectly.

Hope that helps!
 
Old 06-27-2005, 11:37 AM   #4
Genesee
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have you tried copying over the config file for the working configuration to the one that doesn't work? (rename or move the orignal to backup) - and are you sure the horizontal/vertical refresh numbers are right in the config file(s) - check your monitor docs or search online for the right values.
 
Old 06-27-2005, 12:56 PM   #5
hpladd
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TGP,

I'm quite certain that my Debian is newer than the Red Hat, and that Debian somehow recognizes the LCD monitor. But how? The XF86config file for both distros read that the Monitor is a PHILIPS 107T with Sync rates which are correct for 107T. The 107T is the CRT monitor I used prior to the Dell LCD monitor.

(BTW, lilo and command prompt are fine in both distros. The problem arises only in using X).

Unfortunately, I'm not certain what version of Debian I am running as I installed it from the internet. The process failed many times, and I tried several mirrors/versions. Now I'm not quite certain which version actually succeeded. Red Hat is version 9. -- Thanks Much

Genesee,

I thought about copying over the config file as you suggest. Here's the rub -- the working config file shouldn't work. I know that sound like nonsense, but I can read the file, and it clearly identitify the wrong monitor!? So somehow Debian bypasses the XF86config file and runs the monitor with some other (perhaps generic) settings. But from whence those settings come, I do not know -- Thanks Much


MasterCephus,

Did you go into the XF86config file and manually edit? Perhaps you used xf86config? -- Thanks Much
 
Old 06-27-2005, 03:17 PM   #6
Genesee
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don't worry about the text strings used to identify things in the config files - it's the numerical values set that matter. sure you can just edit the config file yourself if you want - backup the old one by renaming it just in case.

another question is whether you are running xfree86 or xorg - the config file for the latter is xorg.conf. check if your debian install is running that instead - if it's reading xorg.conf, you can try just copying that over and renaming it to XF86Config if you want - they are essentially the same thing.
 
Old 06-27-2005, 04:08 PM   #7
MasterCephus
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Quote:
MasterCephus,

Did you go into the XF86config file and manually edit? Perhaps you used xf86config? -- Thanks Much
I am using Fedora, and I am using xorg....
 
Old 06-28-2005, 01:31 AM   #8
J3N7iL
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Thier is something funky going on with fedora and LCD's

My lcd has both DVI and VGA,
After loading my new Nvidia drivers, and rebooting (with DVI hooked up) I got squat, the LCD dident even hit a signal.
I switched to VGA, rebooted and everything works fine.

that, is not noraml.
 
Old 06-28-2005, 10:30 AM   #9
hpladd
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Genesee,

Well, I replaced the Red Hat XF86config file with the one from Debian and the LCD seems to work OK.

I have to confess -- despite mounting evedience to the contrary -- I'm still a bit sceptical.

What I'm most worried about is the HorizSync and he VertRefresh rates they are still set for the CRT monitor. I've read that setting those incorrectly will burn-out your monitor -- at least the CRT monitors.

Thanks for your help. I hope you don't misinterpret my caution as a lack of appreciation. Just don't want to burn-up me new monitor!

Thanks again.
 
Old 06-28-2005, 12:43 PM   #10
Genesee
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good to hear you're getting closer

note you can just edit the config file to include the correct values -- there are several sites online for monitor info, or check the manufacturer's site, etc., also the docs that came with the monitor should list proper sync ranges. then make a backup of the config, and edit the original file directly....

EDIT: I'm not sure about the monitor-burnout. I've heard the same thing regarding CRTs, but as to LCDs...?

Last edited by Genesee; 06-28-2005 at 12:46 PM.
 
Old 06-28-2005, 02:36 PM   #11
hpladd
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Yup definately getting closer.

I am unfamilar with xorg. Investigating it is my next step. Or perhaps I should compare the old config with the new and see what is different between the two.

The Red Hat side of my machine does not display text as well as the Debian side -- especially when working from the command prompt.

Thanks again
 
  


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