Hi everyone,

I set up dual monitors (a 1920x1080 DVI monitor and an old 1024x768 VGA monitor) for Ubuntu 11.04, but one of them is flickering or just blank. However, either of them works fine in a single-monitor configuration. The output of "xrandr -q" is as follows:



And the video card is Radeon HD 6450. Could anyone please help? Thanks.

Some cards need you to use certain channels at a time, ie: the DVI and VGA channels may be the same channel, just a different plug.
Thats a poor way of explaining it, but just because the card has 3 outputs (HDMI, DVI, VGA) doesnt necessarily mean all 3 can be used..
Does the 1080 screen connected to the DVI, have a HDMI port on it? perhaps swapping that to HDMI, and trying again, and/or swapping the VGA to DVI (with an adapter)??

I remember having to do that with a NVIDA card a while back, i have 2x19" and 1x24" working on a HD 5770, with xrandr and fedora, but honestly, it worked out of the box with a fedora install. So ive had very little to do with xrandr..

Are you running the latest drivers? perhaps try swapping from the packaged drivers, to the proprietary drivers?

I don't have any DVI to VGA or HDMI to VGA cable off my hands, so I may not be able to try that. I tried the proprietary ATI driver, but somehow it just contaminated my system and made things break. Were you saying for your nvidia card, multiple monitors attached to one single video card worked?

Correct, in the case of the old nvidia card, was setup as follows

gpu0 (AGP) Geforce 6200 (i think) - 1 x 19" (vga), 1 x 19" (dvi)
gpu1 (PCI) Geforce 6200 (i think) - 1 x 24" (dvi), 1 x 42" plasma (vga)

This used to take some fiddling to get working, some distro's were easier than others.

in the case of my current Radeon HD 5770
gpu0 (PCIe) HD 5770 - 1 x 19" (DVI), 1 x 24" (HDMI), 1x 19" (DisplayPort, with active DP-DVI adapter)

This worked out of the box with Fedora 14/15.

shva, HD6xxx support is relatively new in the kernel. A lot of fixes for those GPUs went into the 3.0.* kernel, so you might want to try something newer than the default kernel in Ubuntu 11.04.

Hi, uhm.. flickering? I do think, without looking up the specs of your vga card, it being a radeon and my personal experience with them is good, in fact I have set up three screens with an extra pci nvidia for the third screen and set them up as one large desktop. iow i can move from screen to screen with mouse, the task bar stays on the middle screen.

my suggestion would be to see if you are not accidentally sending a to high a refresh rate to these screens, try a conservative 60Hz on all screens, and make sure you are not giving it a too high a resolution as well.

hope this will help somewhat

kind regards
Ron

wabbalee,
It sounds to me like adamk75, is on the money.

Perhaps try a few live cd's, id suggest FC15 (as it just worked, for me at least), pay attention to the kernel and driver versions, and see if you can copy the config and replicate on the ubuntu install.