fix (hack) for 30" Cinema HD display dancing pixels

Question

fix (hack) for 30" Cinema HD display dancing pixels

hi all,

Daniel Hartman seems to have figured out what's wrong with the 30" displays that show dancing pixels (or if he hasn't figured it out, he seems to have found a partial solution.)

Since the find is buried in 200+ posts about the problem, I thought I'd start a new thread to point it out. The whole discussion can be found here, but basically the crux of it is that there's a problem with one DVI channel that can be ameliorated by slightly slowing down the refresh rate. Read the post for more detail, but for those running OS X 10.3 or higher, you can use SwitchRes X to slow down the refresh. Here's how:

Install SwitchRes X, then from the SwitchRes Control Panel (located in System Preferences) click "new..." under resolutions>custom. Modify the vertical scan rate to 58 Hz, and make sure to press tab so that the setting 'takes' (little bug). Then click "OK", followed by "apply" in the control panel. Reboot and you'll have a 58Hz full-resolution setting as an option both from the drop-down SwitchRes menu bar icon, and from the Displays icon in system preferences. If you then decide to remove SwitchRes X (using the unistall option in the installer application), the 58Hz setting stays as an option under System Preferences>Displays.

Bear in mind this is a work-around, not an actual repair. For me this got rid of nearly all the pixel anomalies, but my screen will most likely still be sent in for repair/replacement at some point. But for those who can't live without their screen and need a fix now, this just might be the ticket.

Posted on Aug 30, 2005 8:32 PM

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Answer 1

Aug 30, 2005 9:09 PM in response to Gentry Underwood

Actually, I think someone else came up with this idea for on the PC (using powerstrip), but I can't remember what post that was. Glad to know it actually works though - I'll have my sis give it a try as well and see what happens on their rig.

Also, I'd be careful of setting too low of a refresh rate - at some point the monitor won't lock in on the signal, and you might get into a mode where its hard to get back to default. Unless you're feeling adventurous, I wouldn't go much lower than 58Hz.

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Answer 2

Aug 31, 2005 7:00 AM in response to Gentry Underwood

Solution:

Change the color options in preferences to, for example, sRGB and of blue pixels go OUT!!!

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Answer 3

Sep 1, 2005 1:08 PM in response to Francisco Jose Villegas Belo

I don't believe your solution of changing the color profile actually fixes the problem. The anomoly only occurs on certain colors, and the dancingPixels jpeg provided in the other thread really demonstrates this. By changing the color profile, you change the shade of gray transmitted to the monitor. I guarantee that if someone were to remake the image with the sRGB profile selected, then the pixel anomoly would rear its ugly head again.

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Answer 4

SEN

Level 1

15 points

Sep 5, 2005 8:37 AM in response to Gentry Underwood

This fix works great on the two 30" Apple Cinema Displays I tried it on. No more problems with dancing pixels after 3 days of testing.

I guess that's finally the solution to the problem.

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Answer 5

Brandon

Level 1

140 points

Sep 5, 2005 9:30 AM in response to Gentry Underwood

This hack sort of worked. It didn't remove all of the flickering pixels, just reduced the appearence of them.

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Answer 6

SEN

Level 1

15 points

Sep 5, 2005 9:37 AM in response to Brandon

What refresh rate did you set?

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Answer 7

Brandon

Level 1

140 points

Sep 5, 2005 10:08 AM in response to SEN

58hz. It did remove most of the flickering pixels, but some are still there.

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Answer 8

Sep 7, 2005 12:13 AM in response to Gentry Underwood

I did some more experiments to see the limits of what the monitor can sync on. The following settings will give even a bit more margin than the normal 58Hz george talks about.

Horizontal Vertical
Active 2560 1600
Front Porch 48 1
Sync Width 32 4
Back Porch 48 1

Then set the pixel clock to 252MHz and hit tab. Save the settings, reboot, and make sure you select the 58H refresh rate from your display control panel afterwards.

You can probably go a bit lower on the pixel clock (my monitor goes down to 248MHz before totally losing its mind), but its best to leave some margin.

Also, if you want to slow down just a bit but maintain 60Hz refresh (if for some reason you think it matters), use the above porch settings with a 259MHz pixel clock.

Further indication that the dvi channel is flaking out: When I take my pixel clock up to ~278MHz, I finally get dancing pixels with the image George posted, which gets really bad about 280MHz. Anything slower than that is absolutely fine. Above 282MHz, my monitor refuses to lock.

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Answer 9

Sep 7, 2005 11:25 AM in response to Daniel Hartman1

Whoops - sis reported an improperply centered screen with those settings. One should probably use a larger back porch value like 64:

H Active: 2560
H Front Porch: 48
H Sync Width: 32
H Back Porch: 64
V Active: 1600
V Front Porch: 1
V Sync Width: 4
V Back Porch: 1

Pixel Clock: 252 MHz
(this will result in a refresh slightly lower than 58Hz, I believe)

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Answer 10

Sep 10, 2005 6:17 PM in response to Gentry Underwood

Gentlemen and Ladies,

I recently purchased a 30" ACD, ordered a ATI Radeon X800XT card. Once installed, I was happy to see everything working fine until I too became victim of the "dancing pixels" syndrome. This occured approx 30 minutes into turning the monitor on.

I had been researching buying the monitor for quite some time and had followed this thread. So I downloaded SwitchRes X and created a new profile running at 58Hz as the default was set to 59.9Hz.

To my amazement the pixels have not shown their ugly faces again. It has been 5 days of non-stop testing. Zilch.

When I do set the resolution to 2560x1600 at 60Hz they all magically reappear.

Thank you very much Daniel for brining this solution to light. If I had not found this FIX I would have been very disappointed after having spent so much money.

Regards,
Max - One happy 30" ACD owner.

P.S. The monitor is worth every penny 🙂

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Answer 11

SEN

Level 1

15 points

Sep 11, 2005 8:37 AM in response to SEN

Another week went by and it still works flawlessly on both displays.

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Answer 12

Sep 27, 2005 11:41 AM in response to Gentry Underwood

Outstanding Fix!! Thanks for the post. My 30" had all kinds of dancing pixels on the screen especially in my black areas when using Final Cut Pro & After Effects. The SwitchRes 58Hz did the trick!!

What did we ever do before user forums?

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Answer 13

Oct 2, 2005 2:30 AM in response to Gentry Underwood

I'm thinking about buying a 30" display to replace my old 23" display, but after reading all these posts... geesh!

Is the Switch Res solution still working for those of you who tried it?

Has anybody had success using the ATI Display 4.5.5 download?

This sounds like something that could be easily cleared up in driver update from Apple with updated drivers from ATI & Nvidia.

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Answer 14

SEN

Level 1

15 points

Oct 3, 2005 11:37 AM in response to My_Monster_G5

Yep, still works flawlessly for me after all this time.

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Answer 15

Oct 5, 2005 8:28 AM in response to Gentry Underwood

Thanks for the info Gentry and thanks to Daniel for the work-around! I to am having trouble with the dancin` pixels. It is not bad and not all the time. At first I thought the it would start up when the monitors would get warm, but it also disappears after the monitors been on for a while. I have two 30" displays and only see it on one of them. I purchased them at the same time I purchased my G5 so I also purchased the extended warrantee. Unfortunately...Apple will only let you have the extended warrantee on one monitor and not both...which is sad after spending that much money for a system. So what I am getting at...is this something that will get worse as time goes on and can I expect my second monitor to start having this problem after time? I still have about 5 months on my standard warrantee so I assume I should have this looked into. I made the purchase from the Apple store and hate to ship the monitor back, but I am not sure if they will let me take it to the local Apple dealer (Comp USA)...has anyone went through the same scenario on a return?

Thanks,
Mark

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