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Possibly OT, Viewsonic VX922 or KVM box

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    #1

    Possibly OT, Viewsonic VX922 or KVM box

    Do KVM boxes get flaky, or is the problem described below a display issue?

    The Viewsonic VX922 in my office attaches to a Cables to Go 4 port KVM switch, model 35555, like this one:

    http://www.cablestogo.com/product.as...507&sku=35555#

    For the last couple of weeks I have been building PCs and so switching back and forth between the four positions on the KVM frequently. Lately in the morning when I turn everything on for the first time the Viewsonic acts like it is seeing a video signal that it cannot handle. (Nothing on the screen, but not the "no signal" message.) It isn't the two seconds to black sort of problem. The thing is, so far, whenever I get fed up and plug the display directly into the PC it works, which would tend to indicate a KVM problem, but then when I move the display back to the KVM video out jack, and plug one of the 4 KVM video cables into the PC, the display still works! Once everything is warmed up, there are no problems. Or maybe once it has ever worked, there are no problems (which might indicate a driver issue on the graphics card, some of them won't start if they don't see a proper display device). So the results so far are not very clear, as to where the problem lies, other than at least part of it seems to be a warm up issue somewhere.

    The only other symptom I have noticed is that, when hooked up to the KVM, the monitor doesn't always sync up in time to show the BIOS screen. Again, that could be the KVM or the Display.

    Tomorrow I will try to remember to cold start the Viewsonic plugged straight into the PC, if that doesn't work then it is the monitor. If it does, it might be the KVM...

    Yeah, I know, time to open up the KVM and see if there are signs of trouble inside. Hopefully the fault isn't in the Viewsonic, since my only other options are a couple of small 17" LCDs or one of the spare humongous CRT displays.
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    #2
    Re: Possibly OT, Viewsonic VX922 or KVM box

    Your description matches bad caps inside the monitor.
    Originally posted by PeteS in CA
    Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
    A working TV? How boring!

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      #3
      Re: Possibly OT, Viewsonic VX922 or KVM box

      Originally posted by mathog View Post
      Do KVM boxes get flaky, or is the problem described below a display issue?

      Hopefully the fault isn't in the Viewsonic, since my only other options are a couple of small 17" LCDs or one of the spare humongous CRT displays.
      One easy test would be to use the small 17 inch LCD temporarily and see if the problem occurs.
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        #4
        Re: Possibly OT, Viewsonic VX922 or KVM box

        My kvm switch (10yr old belkin omniview 4-port, will cause the mouse to randmoly lock up. And sometimes the monitor stopsmworking. But i have tried it directly commected to the pc and its not the monitor. So i got suspocious and opened up the mvkvm switch.
        And it seemd fine and the tiny rubycon cap was the only one
        kvm switches are useful but can be a pain

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          #5
          Re: Possibly OT, Viewsonic VX922 or KVM box

          Originally posted by shovenose View Post
          kvm switches are useful but can be a pain
          That seems to be the case here too.

          This morning with the LCD display plugged straight into the PC on a cold start it came right up. Have to repeat the experiment for a few more days, but at least initially it looks like the "slow to warm up" component is in the KVM.

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            #6
            Re: Possibly OT, Viewsonic VX922 or KVM box

            This is an odd one.

            With the LCD display plugged straight into the graphics card when it boots I see the BIOS prompt, then Windows booting, then Windows. The thing is, the Grub boot menu should appear for a few seconds after the BIOS, and it does not show up. Today at the first boot I tried making it wait in the grub menu for a while, by hitting up and down arrow keys at the right time, and it never appeared. Immediately, rebooted and dropped into the BIOS menu (hit "del" key) and the BIOS menu wasn't visible either, although the startup BIOS screen was.

            It seems sort of like the 2 seconds to black problem, but only when the PC boots and on low resolution screens. If windows comes up (1280 x 1024) there is no problem. If I change the resolution down to 640 x 480 while in Windows (I guess what the BIOS resolution is) the image stays up.

            Edit: it was actually 720 x 400 @ 70Hz, but changing to that resolution in Windows still left the image on the screen. Leaving it at that resolution, unplugging the power cord on the monitor, wait 5 minutes, plug it back in, and the image comes right up.

            When the KVM was in play the usual failure was that the Windows displays never appeared.

            Going to try another LCD display for the cold boot next week.
            Last edited by mathog; 09-24-2010, 02:42 PM.

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              #7
              Re: Possibly OT, Viewsonic VX922 or KVM box

              Plugged another monitor (an Acer AL1717) into the PC and cold started. This one sees the initial BIOS screen, all subsequent BIOS screens, the grub menu, and the Windows screens. That is, it works correctly.

              The Viewsonic (alone, when cold) sees the initial BIOS screen, none of the subsequent BIOS screens, does not see the Grub menu, but then does see the Windows screens. Once thoroughly warmed up it sees all screens.

              The Viewsonic (plugged into the KVM, when cold) may show nothing, including the Windows screens.

              So I guess the first step is to see what's wrong the Viewsonic. It's a funny sort of glitch, where when cold it seems to have a problem displaying 720 x 400 @70Hz. Not sure why it always shows the initial BIOS screen and none of the latter ones, unless perhaps it changes to a different resolution? The first screen goes by much too quickly to catch the frequencies using the monitor's "info" setting in its menu system, and there is no way to pause it there.

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                #8
                Re: Possibly OT, Viewsonic VX922 or KVM box

                Originally posted by mathog View Post
                P
                So I guess the first step is to see what's wrong the Viewsonic.
                Time to "take it apart".
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                  #9
                  Re: Possibly OT, Viewsonic VX922 or KVM box

                  Originally posted by retiredcaps View Post
                  Time to "take it apart".
                  Just did so. Found these slightly bulging (but not leaking) capacitors on the PS board (FSP043-2P101):

                  C224 Capxon 25V 470uF ~5mmx15mm
                  C261 ditto
                  C263 ditto
                  C244 Capxon 10V 1000uF ~5mmx15mm
                  C241 ditto
                  C242 Capxon 10V 470uF ~7mmx12mm

                  The only other small electrolytic on the PS was C123, 50V 22uF, ~5mm x 11mm. Not bulging, also very hard to read the markings as the letters face the side of a transformer. Plus of course the one large 400V 100uF capacitor, which isn't bulged or leaking, and those usually don't go bad.

                  On the video board there were many small Teapo capacitors, none obviously bulged or leaking. Also two slightly larger green electrolytics, 330uF 16V, not bulged or leaking, couldn't read the manufacturer without taking things apart a lot more.

                  Guess I'll replace all the bulging Capxon's and hope for the best. Should I replace C123 too? C244, C241 and C123 are all partially glopped in place. The others will be easier.

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                    #10
                    Re: Possibly OT, Viewsonic VX922 or KVM box

                    Originally posted by mathog View Post
                    Guess I'll replace all the bulging Capxon's and hope for the best. Should I replace C123 too? C244, C241 and C123 are all partially glopped in place. The others will be easier.
                    Most here will recommend that you replace them all regardless if they are bloated or not. The caps may not meet their uF spec or have high ESR (ohm).
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                      #11
                      Re: Possibly OT, Viewsonic VX922 or KVM box

                      Correction on dimensions:

                      C224 Capxon 25V 470uF ~10mmx15mm
                      C244 Capxon 10V 1000uF ~10mmx15mm

                      Ordered replacements for all PS electrolytics other than the biggest one. In a few days we will know if these were the problem.

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                        #12
                        Re: Possibly OT, Viewsonic VX922 or KVM box

                        Replaced all of these capacitors. The repaired display came up on cold start and showed all BIOS screens and the Grub boot screen. So that seems to have fixed it. Have to wait for a few more days of cold starts to be sure.

                        Interestingly, the temporary replacement LCD display (Acer AL1717) had no problems swapping between PCs through the KVM. It may be that the failing power supply made the VX922 overly touchy about the video coming through the KVM.

                        On a possibly related note, that Acer normally plugs into compute nodes (as needed) through a 6 foot video cable and then a 30ft. KVM cable (but no KVM). When connected that way it has a tendency to fail by refusing to see video until unplugged/replugged. That might be the result of a funny impedance in all that video cable, or perhaps more likely, a slight electrical problem in the room (the compute nodes are not on the same breaker panel as the display). While temporarily in my office it didn't glitch like that once.

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                          #13
                          Re: Possibly OT, Viewsonic VX922 or KVM box

                          Originally posted by mathog View Post
                          The repaired display came up on cold start and showed all BIOS screens and the Grub boot screen. So that seems to have fixed it. Have to wait for a few more days of cold starts to be sure.
                          4 cold boots and no problems noted. So this seems to have just been one more instance of bad caps. The KVM appears to have been blameless, other than acting as a kind of funky video load, which interacted badly with the failing display.

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