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

Top-ranking reply

Daniel Hartman1

Level 2

455 points

Posted on Sep 7, 2005 12:13 AM

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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32 replies

BSteely

Level 5

7,643 points

Feb 7, 2006 7:59 AM in response to Craig Isbell

Nah, if it is only harm to the monitor you are concerned about, don't be concerned at all. There is no added stress to the electronics in the same way that can happen on a CRT monitor if you change the sync timing without care.

There isn't a whole lot of downside to this mod. I suppose when watching a DVD you will have a couple dropped frames every second, but that shouldn't be apparent at all.

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.

Jan 28, 2006 2:01 AM in response to Daniel Brown

I dont know if im right, but since i installed the Mac OSX 10.4.4 i dont see any dancing pixel on my 30"...... ¿?

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.

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.

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.

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

Oct 26, 2005 2:34 PM in response to Gentry Underwood

I just got a new 30" a few days ago. I'm running it on my old Dual 800 G4 with an ATI 9600 pro and I've got dancing pixels galore. Either my video card/G4 combo is not really up to driving this thing or Apple is still shipping units with the issue.

Lawrence

yayolabs

Level 1

30 points

Dec 26, 2005 7:28 AM in response to Rusty Potts

RE: ATI Hotfix

I had the problem when I got my X800XT a few days ago, the fix works. (Running a Dell 2001FP).

So I'm gathering some of you guys are running an ATI card if you're getting the dancing pixels?

blastula

Level 1

0 points

Feb 1, 2006 2:02 PM in response to Gentry Underwood

i returned a 30" that had the flickering blue problem.
got a replacement that's been working swell for a few weeks,
and last night the problem started on the replacement.

this time the flickering blue problem is accompanied by a fun new problem : the monitor actually goes black for in instant (it flickers off and on)....It was sporadic last night...but started coming on hot and heavy this morning...rendering the display unusable.

what's odd is the flickering stops once i tell the computer to restart and the screen goes to blue....also there is no flickering when the computer is booting up.

Feb 6, 2006 11:25 AM in response to Gentry Underwood

I have a 30" CD with the dancing green pixel problem The SwitchRes X solution described in the forum worked flawlessly. My question I guess, is if this works, why should I get my monitor fixed by Apple? Other than a warranty issue, which I know I'm better of sending it in, is there an inherent benefit to running this montior at 60 Hz that I should get it fixed right now or could I run at 58 Hz for the rest of this monitor's life cycle and just be happy?

Anyone know the answer to this? I'm not looking for just an "because it's under warranty stupid" kind of answer. I'm looking for a technical answer, why it would benefit me to run "at full speed" so-to-speak and if it hurts the monitor to run at 58 Hz, etc.

Thanks.

SEN

Level 1

15 points

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

What refresh rate did you set?

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.

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.

Dec 21, 2005 11:58 PM in response to Rusty Potts

Well, but the ATI drivers correct the dancing pixels, the blue pixels????????.

I have a 6800U, is there any solution from NVidia like these?.

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