CAPS v1 flickering screen

[extracampine]

Hi,

 

I've noticed this with my CAPSv1 as long as I can remember, though due to other commitments am only just getting round to looking into it.

 

I have the CAPSv1 (Computer Audiophile - Computer Audiophile Pocket Server - C.A.P.S.), i.e. Intel D945GSEJT motherboard with Intel Graphics Media Accelerator 950 integrated video. I am connected via VGA cable to a 24.1" Asus PA248Q monitor, VGA input.

 

The issue I am having is this - there is a constant kind of banding/flashing/flickering over the entire display. It's not that obvious, though quite noticeable if you sit in front of the monitor for a while or if you know it's there. I was experimenting with colour screen fills in paint, and it seems most noticeable on a grey background. I can't see it at all with black and hardly with white. It's noticeable with a range of colours though, and particularly with greys.

 

I know that it's not the monitor as the display is quite stable when connected to a Macbook.

 

Any help appreciated !

[iago]

Something like a horizontal band slowly moving over the screen from top to bottom (or the other way)? Or something more subtle? The first one is possibly caused by different potentials on the ground planes of connected devices. That would be the video equivalent of a ground loop.

[extracampine]

Something more subtle I would say - it seems horizontal, but it's not just one band moving over the screen - its fast flickering over the entire screen at the same time.

[iago]

My monitors are doing this for the first 30 seconds or so after switching to their working resolution (eg after startup or when woken up from sleep). Apart from that I never noticed flickering in TFT panels.

 

Do you use VGA also to connect to the Macbook? Maybe you get some EMI through the VGA cable.

[extracampine]

Hi, no I use mini-displayport to connect to the Macbook. I'm using the Macbook just now and find it hard to see any flickering.

 

I think VGA is the only video output my CAPS has. Do you think it's EMI causing it? What can I do about this?

[iago]

I think VGA is the only video output my CAPS has. Do you think it's EMI causing it? What can I do about this?

 

Just a remote possibility, but not very probable. I used VGA for years without negative impact. To rule out interference through the cable itself, you should try the same cable with another source into your monitor. The Macbook does not have VGA out anymore, I presume?.

 

Ground loop is still a possibility. Your mains frequency is on 50 Hz, the usual panel has a refresh rate of 60 Hz - should give a 10 Hz difference, which might be visible. I would experiment with short mains cables of same length plugged into the same power strip for monitor and computer.

 

My monitors have a grounded (three-pronged) mains connector, but an ungrounded (figure eight) connector into the external power supply. If your's has the same connector, try inserting it turned around 180 degrees and see if taht helps. The same applies to the C.A.P.S in case this has an ungrounded power supply.

 

My monitors seem to be floating and get their ground connection from the shield of the video cable. Works well, but only if this is the only connection running into the monitor.

 

Are power and VGA cable the only connections running into your monitor, or are there more? Try removing everything else and see if that changes anything.

[extracampine]

Thanks. I tried connecting the monitor to the same power strip as the hifi gear - no difference. I also looked at reversing the caps power plug - but it is 3-pronged so cannot be reversed. I tried a short vga cable in case this was it - but no difference. I have not yet tried covering the cable in tin foil.

 

Any further help appreciated!

[extracampine]

I've just realised something else which may be a big clue - the flickering is much worse when audio is being played though the system. When I hit pause, there is a noticeable reduction in the flickering.

 

Any help or pointers appreciated!!

 

Thanks

[mourip]

I saw this issue with both of my "CAPS-like" servers when using a generic power brick. The noise was very pronounced using VGA and less so with DVI but still there. It went away once I upgraded to a linear power supply.

 

I would get jittery horizontal lines and audible noise especially with mouse movement before I moved to eventual head-less mode...and the LPS.

[extracampine]

Interesting...which linear PS did you get?

[mourip]

Interesting...which linear PS did you get?

 

I got the HD-Plex. Very nice build quality, two outputs (12v and 19v), and lots of connectors.

 

I only wish they had an option to choose one output at 12/19 and then have the other output at 5v...

[extracampine]

Just an update to this thread - I am still looking for support.

 

I have been thinking about this problem with my flickering screen and have maybe come up with another clue to the problem. I had previously had trouble with a high-pitched noise coming from my CAPS (it is actually a CAPSv2 not v1 as the thread title suggests, sorry) - see my other thread regarding this. I eventually managed to solve the noise problem by finding the component inside that was making the noise (it was the "external drive magnetic buzzer", labelled AC-1205GG) and covering the hole on top of it with molten glue. Although this did work, I had the impression at the time that I was only fixing a symptom and not the root cause.

 

I have just put 2 and 2 together, and wonder if my problems with the noise from the CAPS and the flickering screen are related (by related I mean have a common denominator). Both seem to be due to noise/interference coming through a particular component (the above component on the motherboard, and the VGA output). Now I know very little about electrical engineering and the above discoveries were made via googling and help on this forum (as well as Hydrogenaudio). But I wonder if there is a problem with electrical noise in general with my CAPS - perhaps it is not grounded properly or something?

 

If anyone can comment or help me to take this forward it would be greatly appreciated!

 

Thanks

[iago]

Update from my side also.

 

I noticed the same phenomenon with the latest set of (inexpensive) motherboards I tried. There is flickering in some regions of the screen whenever I play audio. The system does not have many connections when sitting on the test bench (VGA cable and cheap 12V power supply). Everything is plugged into the same power strip, so ground loops are not dominant.

 

And it's only noticable when it outputs audio into one of the (onboard or offboard) interfaces.

 

I suspect it's a feature of more recent mainboards. Probably they spend less effort on the VGA interface, because nobody uses it much anymore. Maybe interference between clocks used for audio and VGA pixel frequency?

[extracampine]

Just an update. I have not managed to solve this problem. What I have done is changed my desktop wallpaper to black, and changed the colour settings in my music player (Foobar) to black, with white text. This makes the fuzzy lines much less visible, as they don't really show on a black background. You can still notice it when viewing album artwork though it's less of a problem now.