This section was not included with the install section because many times you can get through the install, but need help fine tuning it. Both of my monitors are not listed as choices during install, and the refresh rate for my given resolution was way too low. I found little clear step by step help for fixing this. To see what i mean please read the video timings HOWTO. You must know the Horizontal and Vertical rates for you monitor. If you do not know look in you manual or email the manufacturer.
First off let me describe my problem. I got through the install fine my diamond stealth 3d 2000 was correctly detected and i choose custom monitor and picked 1024x678 @ 70 since it was closest to what i needed for my CTX 1765 GMe monitor. This worked fine except that the refresh rate was 70 and not the 75 which my eyes could tolerate. I also have a packard bell 1411sl which does not even work right away unless i choose 640x480 @ 60. Through the following steps below you will get you monitor working at a comfortable refresh rate. If for some reason this does not work at all set up your system to use 640x480 at 60 as this will definitely work, and then go complain to RedHat who will gladly help you with your 30 day of free technical support. I am just going to tell you to do certain things and type certain commands that you may not understand, but don't worry you probably won't break anything.
I selected a resolution and Refresh rate that should work but it doesn't?
This is because you video timing in you XF86Config file have to be fiddled with. Take my situation, i choose custom monitor 50-100 vertical refresh and 1024x768 @70 since it matched my set up the closest. I assume you are now looking at a command prompt and are confused yes? Well do this type emacs /etc/X11/XF86Config. you are now in the emacs editor. scroll down with the down arrow to the monitor section and you will notice a bunch resolutions listed with number like 68 1024 1153 168 listed after them. You must now look for a predefined line which seems to be what you want. Remember i choose 1024x768 @70, well below that is a line for 1024x768 @76. Now delete the other resolutions you are not going to ever use or just comment them out with the # sign. Now the only line that is not commented out or deleted says 1024x768 @ 76 with a bunch of numbers. Also check at the top of the section and adjust you Horizontal and Vertical timing and make sure they match you monitor. Hit Control x, then Control c, and answer y. you have now modified your /etc/X11/XF86Config file. type startx and see what happens. nothing huh?? Well it didn't work for me either. Read the next section
Adjusting the dot clock or that number next to "1024x768"
Chances are your dot clock is set too high. You need to adjust the number after "1024x768" or "800x600", whatever your planning on using. At first I tried a higher number say 85 as opposed to 83 then typed startx and nothing worked. I than went in and changed it from 83 to 75. Please change your number based on my example with emacs /etc/X11/XF86Config, change the number, control x, control c, y, and startx. Holy cow it worked! but now my screen is off to the right or left or up or down or whatever and the refresh rate sucks. Hey stop complaining so much...just kidding. Now exit back out and reedit the file and start increasing the number by 1 or 2 and tying again. In my case 80 was the sweet spot , although it can very well be a half number like 79.5. Now your refresh rate should be nice and high and but your screen may be to the right or left or up or down. Read the next section.
Using xvidtune to adjust the image of you monitor
Now that you have a semi usable desktop, once in xwindows fire up a terminal and type exec /usr//X11R6/bin/xvidtune. Now acknowledge the warning and behold the xvidtune utility. Note that the numbers shown match the number in you XF86Config file. Also notice the bottom right number which shows your vertical refresh rate. Now if your screen if to the right click the "left" button box. Now hit test. Notice how your screen moved a little to the left. Keeping doing this to center to screen. Notice how the numbers are changing above the slider bars. This utility if only for testing purposes , it does not edit you XF86Config file as it goes along. You and bound to notice that if you say click widen like 10 time in a row and then hit test it screws everything up, you many even have to log out then back into xwindows. this is normal. They key is to do it one step at a time while making note of the numbers. after you get to the point where it is centered and maxed out to the point where one more adjustment messes everything up, you have just done your video timings. Edit your XF86Config file with the numbers that work and restart you xwindows. Note that sometimes no matter what you must go back and try a slightly different dot clock rate, but this hopefully will not be necessary. Also if you are using xvidtune and you really messed up just hit control alt backspace as this will kill you xwindows session. I hope you are now happy with your display. Like I said if this does not work email RedHat or post a question on the net. If you afraid of newsgroups try clubs.yahoo.com in the Linux section. You can join them and post easily. One last possibility is you can purchase a commercial xserver from XI Graphics, or Metro X which make this process even easier, Laptop users should note that for them this may be needed to even use Xwindows if your graphics chip is not supported in XFree86.