major screen flicker when using kvm

Another data point:

=== Me:
- New Al MacBook Pro 15".
- New Mini-DisplayPort to DVI Adapter.
- Viewsonic VP201b LCD, ~4yrs? old.
- DVI cable, apparently shielded & of moderate quality.
- No KVM involved. Notebook -> DP/DVI Adapter -> Monitor DVI-D input.
- Native Resolutions: Notebook: 1440x900. LCD: 1600x1200.

=== Problem:
Lots of snow / flicker on the external display over any black regions. It looks kind of like I need to adjust my antenna to tune in a distant UHF TV station. Horribly distracting.

=== Ineffective Solutions:
- Unplug / replug all cables. (No effect).
- Try with / without AC power connected. (No effect).
- Reverse ends of DVI cable. (No effect).
- Power cycle monitor / notebook. (No effect).
- Move other windows around on screen. (No effect).

=== Effective Solutions:
1. When I use the GeForce 9400M ("Better Battery Life"), I get lots of snow.
When I switch to GeForce 9600M ("Higher Performance") (and log out/in again), the snow disappears. I didn't leave it on the 9600M for more than a minute, so it's possible the snow would eventually return. But this is the first change that had any impact on the problem.
2. Additionally, reducing resolution to 1024x768 or below eliminates all snow.
Neither of these solutions are really acceptable.

=== Things I haven't tried that might help:
- Different DVI cable.
- Different monitors (only VGA conveniently available right now).
- Mini-DisplayPort -> VGA adapter.
- Other DVI sources for this monitor (MBP is first DVI source).

=== Thoughts
This problem may be exaggerated by KVMs, but it seems to go deeper than that. If you guys can try your setups with 9600M vs 9400M, that might be useful data, as it is the one thing that made the most difference in my case so far.

I have two issues, one is a use a KVM and a Dell 2405FW and I can no longer use the KVM.

I also have a samsung ay home and it does not sync at all after wake up , this is very dissapointing considering the video is main reason I updated.

I am having the same problem using a Apple Cinema Display 23" but I seem to have some inconsistencies with ogdoad8 above.

I just spoke to IOGEAR and they told me that they haven't yet tested the IOGEAR 1764 4-port DVI KVM with the new Macbook Pro but are aware that there is some sort of incompatibility.

I find that when the Cinema Display is plugged in directly to the MBP, everything works perfectly.

Here are my findings...

=== Me:
- New Al MacBook Pro 15".
- New Mini-DisplayPort to DVI Adapter.
- Apple Cinema Display 23"
- Standard IOGEAR KVM DVI/USB cable
- IOGEAR 1764 4-port DVI KVM. Macbook Pro -> DP/DVI Adapter -> IOGEAR 1764 (Any Port/Any Cable). Cinema Display -> IOGEAR KVM DVI Output
- Native Resolutions: Notebook: 1440x900. LCD: 1920x1200.

=== Problem
Lots of greenish snow / flicker on the external display over any DARK regions. Horribly distracting.

=== Ineffective Solutions:
- Unplug / replug all cables. (No effect).
- Try with / without AC power connected. (No effect).
- Power cycle monitor / notebook. (No effect).
- Move other windows around on screen. (No effect).
- Switching cables or Ports on the KVM (PC and other macbook work fine with any cable/any port) (Port 1 seems to be worse than the others)

- HIS SOLUTION IS COMPLETELY INEFFECTIVE FOR ME "When I use the GeForce 9400M ("Better Battery Life"), I get lots of snow. When I switch to GeForce 9600M ("Higher performance") (and log out/in again), the snow disappears. I didn't leave it on the 9600M for more than a minute, so it's possible the snow would eventually return. But this is the first change that had any impact on the problem.

- HIS OTHER SOLUTION ALSO INEFFECTIVE FOR ME "Additionally, reducing resolution to 1024x768 or below eliminates all snow. Neither of these solutions are really acceptable." (I see the same video problems, through the KVM, all the way down to 640x480.)

=== Effective Solutions:

Plug the Cinema Display directly into the Macbook Pro - Works as it's intended only I lose KVM functionality.

Using a port other than port number 1 on the KVM results in significantly LESS snow, but not none. IOGEAR said they'd call me when they fix problem (firmware upgrade??? - I can only hope!)

Just thought I'd add my two cents - seems it's been a while since there's been a new post in this thread. For those of you checking back here, however, new posts are being submitted to the "macbook pro and apple cd 23" thread and "problems with external displays on the macbook pro threads" that closely resemble all of the problems we're experiencing with kvm's. Near as I can tell, the general consensus is that it is software problem that plagues all sorts of external displays. It seems some at Apple are aware of the issue, but not necessarily every tech you might speak with. One user reported being told that a software fix should be out before Christmas that will address a variety of external display issues.

I can report that the IO Gear KVM mentioned several times below is not the only problematic KVM as I use a Belkin DVI-D switch with some very glitchy success. It doesn't work well with longer of the two DVI cables (not sure why though, as my work provided HP looks great on it) and whenever I switch off the MBP and then back again I have to cycle the display in and out of sleep several times to stabilize the picture (I use the Shift-Ctrl-Eject shortcut because I often can't see the screen well enough to make sure of Hot Corners). I can't decide if it's more annoying to do this or just plug and unplug everything each time.

hi! thanks for posting!

yes, i am checking this and the other posts you mentioned - and of course waiting for the patch to arrive. that's great news and based on the number of people experiencing the issues we've discussed, i know it can't come soon enough!

hopefully santa will make it happen!

-dave

Just wanted to say I stand corrected. The update in combination with running the 9600m graphics card (higher performance graphics setting in energy saver) appears to have solved my issues. My MacBook Pro and 23" Apple Cinema Display now seem work great with the Belkin DVI-D KVM Flip and my work HP. I wish I could switch the graphic card on the fly or that the MacBook Pro would auto adjust depending on power source, but I'll definitely take what I can get.

I don't know if I found the solution of I am just masking the problem but..... IT WORKS


I have Macbook pro 2.4 (late 08) and a Monitor DELL 2405FPW.
I just got the IOGEAR GCS1764 last night and I had the same issue that everyone describes in here.

After several hours reading, calling IOGEAR people and experimenting (IOGEAR people just told me to quit) I was able to use the KVM with decent video.

I am connecting the port number 2, I use the high end video card, BUT the real key to clean this up is to calibrate the “color” on the display options.......... System Preferences, Displays, color, calibrate, (make sure you select “expert mode”) and play with the “FIVE” calibration options to make the snow and flickering disappear.
I played with these options having several applications open to be sure all were clean.

Message was edited by: robertogarcia

Message was edited by: robertogarcia

I don't think the calibration exercise is a real solution. I accept that you may be able to mask the pixelation somewhat but I don't think it will standup to some real video tests. If it does though, you won the lottery.

Look the Mini DisplayPort has HDCP built in and the GCS1764 does not support it. This technology was made to mess up unrecognised devices and the switch doesn't communicate using this protocol. IT like trying to record off you DVD output (for the less technical). To get HDCP support you need the GCS1204 or the GCS1784 and you are talking $350 and $450 respectively since they are Dual DVI devices.

Sigh, I'll limp along with the switch on the monitor for awhile.

I think that you have completely nailed what the problem is. It explains why some monitors work with the adapter, and some don't. It explains why, with my gateway FHD2400 and NO kvm, it works beautifully, and why, with the KVM, it is completely horrid.

It also explains why, at some resolutions (mainly, 1024x768 & below), it works correctly.

I hadn't thought that HDCP would matter with just display the computer image, but that does in fact appear to be the case.

It sounds like this is something that apple can't (or won't fix), since it is the copy protection.

Now that I know what the problem likely is, I can make a better decision as to how to proceed.

Thanks Hank!

PS--
I wish I could give you at least a "helpful", but it is not my thread 😉

As a followup to anyone else looking at this thread-

I ordered a new KVM from CDW yesterday, got it today, and it works like a champ!

No more flicker, plus it supports dual-link, so if I upgrade my monitor in the future to a behemoth 30" it should still work.

As a bonus, the eject key on my keyboard works now (the old kvm that I had didn't pass the code thru)

The new one that I got is the IOGear GCS1204.

Comes with the cables and everything.

Thank you! That is incredibly helpful. I am willing to pay the price but not for something that doesn't work. It does work though! I appreciate you sharing the information.

There was a recent drop ont he prices for the IOGear stuff too. The two switches that support HDCP are the GCS1204 (Stereo Audio support) and the GCS1784 (5.1 Audio Support). They are both down to $350 at ANTOnline or $399 at New Egg.

The 1204 makes a lot of sense. You don't have all the cable mess (if you don't intend to put back channel speakers in your office). I don't.

You get the gold star in my book!

I tested a new switch that supports HDCP passthrough as well and it works.

Let's be clear to everyone who reads this. This is a case of Apple adding the HDCP (copy protecting) scheme to their computers and it limiting the use of those computers for those who buy them. It should be known that if you want a MacBook with a Mini DisplayPort to work with a video device properly it should have HDCP support and that will make it more expensive.

It also means that old equipment that you have will may not work well, even for non-video applications. You should know how HDCP works and how it limits the use of your computer. I have no fundamental issue with limiting piracy but who defines what is "fair use" comes into play here.

In my view, this should be something that you know before you buy (or else it should be grounds for a refund).

Hi,

I also have a major screen flicker and snow on my external Dell 24. I have ordered another DVI connector to see if that might fix the problem. This is a bummer. What to do now?

Does it make any difference whether the power supply is connected, and whether the ungrounded two-prong plug or the grounded extension cable is used?