Monitor doesn't display anything. EDID trouble ?

[Alex Deucher]

On Mon, Oct 24, 2011 at 4:49 PM, Xavier Bestel <xavier.bestel at free.fr> wrote:
> Le lundi 24 octobre 2011 à 15:16 -0400, Alex Deucher a écrit :
>> On Mon, Oct 24, 2011 at 3:01 PM, Xavier Bestel <xavier.bestel at free.fr> wrote:
>> > Hi,
>> >
>> > I know it may be off-topic, but the experience is there.
>> > I've just bought a used 30" monitor (HP ZR30w), and it doesn't display
>> > anything, even at BIOS time. The backlight is on, but I see nothing
>> > except a faint flickering at mode change times. Screen blanking works
>> > (the backlight switches off). I'm using a Radeon HD 5700 via DVI,
>> > debian/sid with kernel 3.1.0-rc7, Xorg 2:1.11.1.901-2 and radeon
>> > 1:6.14.2-2.
>> > After googling a bit, some people talk about a possible EDID problem
>> > (apparently it's possible to have the EDID somehow erased from the
>> > EEPROM ?). But Xorg.0.log does seem indicate that there's an EDID:
>> >
>> > [    21.829] (II) RADEON(0): Monitor name: HP ZR30w
>> > [    21.829] (II) RADEON(0): Serial No: CN4048041Z
>> > [    21.829] (II) RADEON(0): EDID (in hex):
>> > [    21.829] (II) RADEON(0):    00ffffffffffff0022f06e2801010101
>> > [    21.829] (II) RADEON(0):    3014010380402878ea8d85ad4f35b125
>> > [    21.829] (II) RADEON(0):    0e505400000001010101010101010101
>> > [    21.829] (II) RADEON(0):    010101010101e26800a0a0402e603020
>> > [    21.829] (II) RADEON(0):    360081902100001abc1b00a050201730
>> > [    21.829] (II) RADEON(0):    3020360081902100001a000000fc0048
>> > [    21.829] (II) RADEON(0):    50205a523330770a20202020000000ff
>> > [    21.829] (II) RADEON(0):    00434e343034383034315a0a20200066
>> > [    21.829] (II) RADEON(0): Printing probed modes for output DVI-0
>> > [    21.829] (II) RADEON(0): Modeline "2560x1600"x60.0  268.50  2560 2608 2640 2720  1600 1603 1609 1646 +hsync -vsync (98.7 kHz)
>> > [    21.829] (II) RADEON(0): Modeline "1280x800"x59.9   71.00  1280 1328 1360 1440  800 803 809 823 +hsync -vsync (49.3 kHz)
>> >
>> > ... and then:
>> >
>> > [    21.854] (II) RADEON(0): Output DVI-0 using initial mode 2560x1600
>> >
>> > Does anyone have an idea how I could pinpoint the problem ?
>>
>> The EDID looks ok to me.  Do any other modes work?  Try 1280x800.  Try
>> the other DVI port.  If the neither port lights up the monitor
>> (especially if the bios produces no display), it's probably a bad
>> monitor.
>
> OK, thanks to you I've found the problems:
> 1) this monitor is apparently unable to display anything but 1280x800 or
> 2560x1600, so no BIOS nor GRUB for me.

You should still get a BIOS image.  The vbios takes the preferred mode
from the monitor's EDID and uses the scaler to fake the legacy modes.
It's probably trying to use 2560x1600 mode which requires a dual link
cable.

Alex

> 2) my cable is single-link, so Xorg's default guess doesn't work.
>
> After hooking a second monitor, and choosing 1280x800 for the big one,
> everything's working (sort-of). I'll hunt for a dual-link or displayport
> cable, whichever is cheapest.
>
> Can Xorg/radeon detect that the DVI cable is single-link ?
>
>
> Thanks,
>        Xav
>
>