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Sparklies on DVI ... is it the cables or Gefen Switcher to blame?

Discussion in 'Cables & Switches' started by StooMonster, Sep 6, 2005.

  1. StooMonster

    StooMonster
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    Today I received a Gefen "DL Switcher" EXT-DVI-241DL; a replacement for the now discontinued Gefen "DVI DL Switcher" EXT-DVI-DL-241 (a model that didn't work with some Apple Macs) and have a sparklies problem -- on both inputs, or perhaps the output.

    Input #1: PC with ATi FireGL V7100
    Input #2: Mac 17” laptop
    Output: Apple 30” Cinema display = 2560x1600 @ 60Hz

    Tried using the equalization adjustors to no avail, makes sparklies go green one rotation and blue in the other direction! I have changed EQ1 and EQ2 equalization adjustors and got the least sparklies, but I still have random pixels of flickering colour on my display.

    I have used the Dual-link DVI cables Gefen provided, and they are labeled 'Gefen DL DVI'. I have moved all power supplies away from cables. I turn off my radio network. On PC I’ve set ATi’s high-resolution screen output to use lower frequencies. All to no avail, sparklies are on Mac and PC input!

    I do not get any kind of sparklies with the screen plugged directly into Mac or PC; I also go no sparklies with old EXT-DVI-DL-241, shame it didn't work with the Mac.

    Also, when the PC is booting the BIOS screen also when the WinXP splash screen is displayed, they are doubled up vertically and covered in so many sparkly pixels they can barely be seen. When using direct connect or the previous EXT-DVI-DL-241 this didn’t happen and I got complete PC compatibility … no messed up DOS screens.

    Gefen's website says “No loss of image quality when switching” and I am still waiting for email response from their technical support. So thought I would come here for your input. :devil:

    So, are sparklies most likely caused by the cables or the switcher?

    Links:
    Gefen “DVI DL Switcher” EXT-DVI-DL-241 [discontinued] used a Silicon Image DVI chipset http://www.gefen.com/kvm/product.jsp?prod_id=2625
    Gefen “DL Switcher” EXT-DVI-241DL uses a different DVI chipset http://www.gefen.com/kvm/product.jsp?prod_id=2950


    StooMonster
     
  2. Joe Fernand

    Joe Fernand
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    StooMonster

    Can you try one of the 'supplied' cables between your source(s) and your Display?

    Joe
     
  3. StooMonster

    StooMonster
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    Joe, the Apple 30" Cinema Display has a built in dual-link DVI cable; can not use any other.

    When the display's built in cable is plugged directly into PC or Mac there are no sparklies.

    Also noticed that if sparklies are in say a photo on a web-page, and one scrolls the window around the sparklies stay in the same place in photo. Or if one uses Photoshop and changes colours of an image, the sparklies appear at certain colours and remain in same place when moving the window around.

    It's got to be the cables to the switcher, or the output from the switcher I recon.

    StooMonster
     
  4. Joe Fernand

    Joe Fernand
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    Hello StooMonster

    Just fishing for ideas!

    What happens if you fire up PC > Switcher > Studio monitor - without 'the MAC' being connected to the switcher.

    Joe
     
  5. StooMonster

    StooMonster
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    I know and appreciate it, don't mean messages to say otherwise; concise and to the point was plan.

    Still get sparklies once booted into Windows desktop 2560x1600 -- and 'DOS' screens are still vertically doubled and practically invisible due to pixel noise.

    All the cables (USB, dual-link DVI, power) are the new blue Gefen ones.

    Two things strike me as odd:

    Firstly, when all KVM connections are present on switcher but no 5V power is connected the red 'power' LED is illuminated. Futhermore, if one plugs in the powerpack, but not the mains lead, the green LED on the powerpack is also illuminated ... it looks like the device and it's powerpack are on, but without a power lead. :( This suggests to me that there's some kind of short-circuit in the design or this switcher is faulty.

    Secondly, there are posts on Gefen forums from people with similar problems; here are three with dual-link Apple 30" Cinema Display:
    http://forum.gefen.com/topic.asp?TOPIC_ID=257
    http://forum.gefen.com/topic.asp?TOPIC_ID=248
    http://forum.gefen.com/topic.asp?TOPIC_ID=32 (second to last post)

    Apple 30" Cinema Display is the cheapest and most common dual-link DVI monitor on the market, one would think there would be rock solid compatibility with Gefen's Dual-link Switcher.

    Puzzled? :lease:

    StooMonster

    PS: I am guessing that you can supply Gefen product, if I'd known before I would've ordered from you!
     
  6. Joe Fernand

    Joe Fernand
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    Hello StooMonster

    I think I need to up our advertising spend :)

    The power LED can de disconcerting - though I'm positive its being powered by the DVI output socket on your source; there are voltages on some of the DVI pins to power external triggers and the like; most of the Gefen boxes 'light up' once a source is On.

    It definitely sounds more like a compatibility issue and not a 'fault' with your switcher - hopefully everyone at Gefen Tech Support is not off at CEDIA today!

    I've copied your Thread to someone in the know at Gefen - just in case CEDIA has depleted the Tech support team.

    I'll get back to you if I get any more info.

    Best regards

    Joe
     
  7. StooMonster

    StooMonster
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    I have attached four photos:

    Gefen1.jpg = PC BIOS boot screen (note double image and noise)

    Gefen2.jpg = PC OS loader (note double image and noise)

    Gefen3.jpg = WinXP splash screen (note double image and noise)

    Gefen4.jpg = WinXP signon screen, zoomed to bottom (note green sparklies, and this is with 'least' sparklies using Equalization knobs)

    This is very frustrating as I so want it to work, and older 'EXT-DVI-DL-241' had so sparklies (just didn't work with Macintosh).

    Thanks for your help Joe!

    StooMonster
     

    Attached Files:

  8. Joe Fernand

    Joe Fernand
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    Hello StooMonster

    I asked Mr H.Gefen to have a look at your post and he's asked me to copy his thoughts to you.

    Joe;

    It is not a problem with Gefen tech guys being at CEDIA or not. The
    problem is that it suppose to work and it does not do the job for the
    customer. We already replaced his unit so it is not a hardware issue
    and I am sure the DVI cables are good as well (what can be wrong with
    the cables?). So this becomes a system issue where this particular
    system is producing "sparkalies" as you call it while other most
    system don't. As the customer posted, others have indicated similar
    problems in the past, so it means that we don't have a handle on 100%
    of the situations.

    The question is what to offer the customer and unfortunately we don't
    have anything else other than to try the DVI-DL-Booster placing it
    in-front of the input to the switcher. Since the customer is
    unhappy, we could return his money. If not than we should try the
    booster before the inputs idea or place a booster after the output
    between the display and the switcher.

    Best regards

    H.Gefen.


    So Gefen have a bit more work to do to fully understand this technical limitation and the first option looks like you place a request with Gefen and they will ship the DVI-DL-Booster for you to try in your system.

    Maybe not the answer you were hoping for but it looks like Gefen are willing to work with you on this one.

    Best regards

    Joe
     
  9. StooMonster

    StooMonster
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    I would be delighted to work with Gefen to resolve this issue, I've done plenty of hardware beta-testing in the past so am familiar with technical problem solving; I'll telephone their support rather than email them tomorrow.

    Point of clarification: they haven't replaced my EXT-DVI-241DL this is the first one I've had, so it could be hardware failure. This unit replaced the EXT-DVI-DL-241 which their telephone technical support told me did not work with Apple 17" Powerbooks (and it didn't, it gave black screen) and was the reason it was withdrawn from sale. However, the two EXT-DVI-DL-241 units I've had worked perfectly with PC's ATi FireGL V7100 card and had no sparklies or sync problems.

    The technical support also told me that EXT-DVI-241DL uses a different manufacturer's DVI chipset to the Silicon Image one in the EXT-DVI-DL-241 model and is a completely different piece of hardware; hence it being half the price.

    It strikes me as odd that both inputs appears to have sparklies, so I think it may be an output problem. I would love to try a Dual-link DVI Booster between the DL Switcher and the display, hopefully they'll lend me one to test!

    I would also like to test the Dual-link DVI cables with alternatives, but don't really want to splash out £100s in doing so -- from what I understand RFI can cause sparklies over DVI cables, although I am sure these Gefen ones are properly shielded.

    Just thought about another test: you asked me to test switcher with just PC plugged in, I will do the same with just the Mac.

    StooMonster
     
  10. Toekiller

    Toekiller
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    Are sparklies there at lower resolutions?

    Can you change the masking rate with apple drivers?
     
  11. StooMonster

    StooMonster
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    Yep.

    Que? Microsoft Windows XP detects it as 'Play and Play monitor' not drives here. Apple OS X says 'monitor 1'

    Update

    'DL Switcher' device itself
    Device is obviously EXT-DVI-241DL 'DL Swticher' model as it takes 5V (as opposed to 24V), has Equalisation switches on front (as opposed to none), works with Apple 17" Powerbook (as opposed to not), the manual is 'DL Switcher manual', and the packing list reports it as such ;).

    However, the artwork on the front of device says 'DVI DL Switcher' and the product name on the back also says 'DVI DL Switcher' -- as opposed to 'DL Switcher' which is what it is.

    Confusing.

    Partial solution
    Apple 30” Cinema Display has captive DVI lead and it’s never had any sparklies problems at all; no matter what I’ve plugged into it. The sparklies are altered by changing the Equalisation Settings for each input on the front. This makes me think the problem is with the input rather than the output, although I could be wrong.

    Thinking about what causes sparklies (data transmission errors) I wondered what could cause them.
    • Long DVI cables
    • DVI cable's shielding being overwhelmed by huge RFI / EFI
    • Poor quality DVI cables with little shielding
    • Poor quality power to device.
    Long cables? Nope this two 6' Gefen Dual-Link DVI cables came packaged with the switcher; and that is well within length tolerance. These cables are thinner and more flexible than previous DL DVI cables included with the other switchers.

    RFI/EMI? Turned off my 802.11g network, and I have several RFI/EFI removal devices on my mains rings. But still got sparklies.

    The 'DL Switcher' comes with EXT-PS54AU (5VDC 4amp Universal Power Supply) in blue plastic ... the same blue that all the cables are now sheathed in, which matches the blue branding on the device. Look nice!

    Tried mains-cleaner next to power socket of PSU; also tried using different ring-main for PSU. Still got sparklies.

    Hrm thinks I ... that 5VDC power-cable crosses over the DVI cables. So I turned the switcher upside down so I could run the PSU’s power-cable in from wall socket and DVIs to screen/sources without power and DVI cables crossing.

    This equalled reduced sparklies.

    That's interesting thinks I ... and wrapped the 5VDC lead inside a spare ferrite core.

    This equalled greatly reduced sparklies; they are now only visible on areas of absolute black pixels. Better, but areas of black are scattered with patterns of blue pixels, or green if I twizzle the EQ switch.

    Go figure.

    Next Steps
    I don't want my money back; I want a working dual-link capable DVI switcher. However, I don’t want any sparklies at all.

    I am thinking that first next step is add more ferrites to 5VDC cable, of different frequency blockers. Second step is to try some other dual-link DVI cables. Lastly I think I’ll try a signal booster.

    I’ll email Gefen support and let them know my discovery too, they wrote back to me mentioning the power LEDs (saying same thing as Joe) but didn’t mention the sparklies at all! However, it was the LED power thing email that got me thinking about the 5VDC power cable crossing the DVI cables.

    StooMonster
     
  12. Mark Grant

    Mark Grant
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    Hello Stoo,

    Maybe try a different power supply if you can find one suitable to see if that helps.

    4 amps at 5 VDC might not be easy to find though.

    Do you have any test equipment to see if it outputs a nice smooth 5 VDC under load? ( if 5VDC is what is needed by the switcher of course! )


    Good luck !

    Mark.
     
  13. StooMonster

    StooMonster
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    Hello mate!

    For other equipment I have got Russ Andrews to make me up one of their Kimber cable custom PowerPaks, and they're excellent albeit a tad expensive (about £90); hence cheap and chearful solution of using ferrite cores.

    Unfortunately, the only tester I have is a circuit tester; but I'll give it a go on the 5VDC.

    Once I can work out if it's the DVI cables or the PSU that's causing problem I'll know where to spent my cash. Trouble is I don't really want to waste money finding out what is the cause of the problem. In case it's neither of those I'll look at boosting the signal.

    StooMonster
     

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