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-   -   Two Quadro 5600 cards yield different brightness over DVI-D?? (http://www.nvnews.net/vbulletin/showthread.php?t=132170)

stuartlevy 04-29-09 01:08 AM

Two Quadro 5600 cards yield different brightness over DVI-D??
 
1 Attachment(s)
Setup:
Linux x86_64 system (RHEL5.3).
Tried both nVidia 177.70.35 and 180.29 drivers.
Quadroplex model IV -- two Quadro FX 5600 cards.
Two JVC 4K projectors.
Each 5600's two DVI-D outputs go to two of the 4 inputs of
one projector.

All four outputs run in 2048x2400 @ 60Hz (dual link) mode.

The cards are identically configured as far as I can see.
A G-Sync card is attached to them both, but the symptom
below appears whether I enable sync or not.

X configured as two separate 4096x2400 screens,
with each card driving one screen. No Xinerama.

Problem:
Even when feeding the same image to both cards,
one output is about 70% of the brightness of the other.

I'd assumed it was a projector problem, but no:
when I swap projectors, and swap cables, the dimness
follows the graphics card.

I can test the relative brightness by simply dimming
all pixels on the brighter card to 70% of normal
(I do this using XF86VidModeSetGammaRamp().),
and showing e.g. grayscale ramps on each projector.
When dimming the brighter to 70%, the two ramps
look pretty similar across their ranges.

What could cause this? It's especially weird
since it's not an analog problem -- all the signal paths
are DVI-D. "nvidia-settings -q all" shows nearly the same
settings for both cards as far as I can tell. Only differences
seem to be:
'FSAAAppControlled' is 1 on one card, 0 on the other;
'FrameLockSyncReady' is on 1 on one card, 0 on the other;
'MultiGpuDisplayOwner' is 0 on one card, 1 on the other.
Dunno whether this is a clue.

As noted above, I've tried both 180.29 and 177.70.35 drivers;
both give the same results. I'm attaching the nvidia-bug-report.log
from the 177.70.35 installation.

What on earth could cause this?


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