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Thread: KVM switch question




  1. #11
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    One more question on the KVM subject...

    I have two boxes on the KVM, my XP machine and then a Linux machine. When I turn the switch to change to the other box, sometimes I lose my keyboard. The Num Lock, Caps Lock, and Scroll Lock light up (and stay lit up), and then I'm unable to use the keyboard on either machine without resetting. However, the mouse and the monitor have no problems going back and forth. Any ideas as to why this happens?

  2. #12
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    There are two types of KVM's, the first one is the old, crappy kind, and probably what you have.

    1: Physical Switches

    You turn a knob, and if physically disconnects the keyboard and mouse circuits, as well as vga and then reconnects them as the knob rotates. One thing that will tip you off is your monitor will flicker OFF for an instant as you turn the knob. If you have a valulable monitor and this type of KVM I would seriously suggest just getting a cheap second monitor, keyboard, and mouse for your Linux box, or you might ruin your current monitor.

    2: Silicon/PCB Switches

    These are the expensive ones, they actually are far far better. What they do is recieve every refresh of the screen, and then as you switch from one to the next it just replaces PC1 screen refresh's with PC2. The Monitor doesn't know anything happened. Which is much healtier for the monitor. Another benefit is that you can switch monitors from the keyboard, this is brand specific, but you can switch monitors by hitting for example CTRL-Q-(PC #) Which can be very handy if you have a 20 computer KVM system.

    Cybex is the king of KVM's. Belkin have models out that suck. Lets face it Just about everything belkin makes sucks--except their cables. Linksys also has some models out, which are probably pretty good as well, but I have not used them or read anything on them.

    You can skimp and use the cheapest PS2 cables you can find with no consequences, but DO NOT skimp on the VGA cables. a 6 foot section of VGA cable that can effectivly handle better than 1024 will cost at least 15 bucks each. (US Dollars)

  3. #13
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    Your Keyboard problem is probably caused by a little corrotion on the mecanical contacts of the physical switch type you have. Either that, or the computer is confused (and rightly so) by the slight sudden drain of power it recieves as the switch is rotated into contact and the keyboard and its LED's are powered up again.

  4. #14
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    Gotcha. Any specific type of KVM you'd recommend by Cybex? I'd rather not get a new monitor/mouse/keyboard. Partially due to cost and partially due to space.

    I bought some new cable today and some pipe insulation. I skimped on the cable first time around... bought two 15' vga cables that costed about $4 each. This time got 2 6' vga cables for $15 each. I'll see how that goes.

    Here is the KVM I bought: http://www.kdcomputers.com/eui/prime/profile/291.htm

    Didn't say much about the specs, but it was only $20 so I figured what the hell. Comparing the price of mine with some of the others, it's gotta be the "old crappy kind" lol.

  5. #15
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    That's about on par with my KVM.
    I never use it to switch between 2 running PC's but rather shut down 1 system, change the switch and boot the other system.
    Some of the older motherboards don't handle the hot-switching at all, and really do require a higher quality KVM switch that emulates the keyboard and mouse.

    But when I use it within the parameters I described, it does fine.
    The reason a diamond shines so brightly is because it has many facets which reflect light.

  6. #16
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    Would a newer keyboard have less problems switching back and forth then, even on my KVM? Still having problems with the resolution, but I'm going to take a couple day break from it before trying again.

    Also, just curious... how can switching over on the KVM be any worse on the monitor than resetting the computer? Doesn't resetting do the same thing? My monitor goes into powersave mode before coming back on too.

  7. #17
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    There is nothng wrong with your keyboard. The wise money would be spent on a KVM switch capable of emulating.

    When you boot your computer it goes through the POST process, in other words it becomes aware and takes inventory of it's components. It is during a small portion of this process that it recognizes it has a keyboard connected and takes the necessary steps to utilize it as an input device.

    When you switch your KVM over to your other system you in essence cut the vital link of the keyboard to your motherboard. A great number of motherboards are unable to cope with the link being broken and then restored, and have to POST again to find and make use of a keyboard.

    You need a KVM that is capable of emulation. In other words, the KVM switch will fool the motherboard into believing there is always a mouse and keyboard connected, even when there is not. That way the link is never broken and when you switch back to that system the motherboard utilizes the keyboard because it is unaware that it actually had it taken away.

    The heart of your problem is actually a limitation in the motherboard, a very common limitation that most motherboards have. A higher quality KVM switch is designed to overcome this limitation by using emulation.

    I speak from experience, My KVM switch is quite similar to yours. I only use it to switch to another system before I boot the system.
    It is incapable of switching consistently between 2 running systems, and in doing so there is a possibility of damaging the motherboard as it was never designed to actually remove and replace input devices while running.

    There is nothing wrong with your motherboard or KVM switch but they do have limitations. Unfortunately, if this is the manner you need to utilize a KVM switch in, this is definitely not the switch you need.
    Keep the keyboard you have and save your money for a better KVM switch. You really must get one that will emulate.
    The reason a diamond shines so brightly is because it has many facets which reflect light.

  8. #18
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    Response to Yohan:

    No, it is very different. See the KVM type you have is nothing but a rotating switch, which means that the electical contacts within the switch are disconnected and then almost immediatly reconnected as the knob is turned.

    The best thing you can do, apart from getting a better KVM, (or a second monitor) is to shut the monitor off, switch the connection, and then turn the monitor back on. That in itself can be harmful if it is done 40 times a day.

  9. #19
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    Okay, I see. So restarting doesn't hurt the monitor, because unlike the KVM, it doesn't actually kill the electric connection to the monitor then? Sorry to bother you with all the questions, but I still have another:-) Before the KVM, I would just start up both systems and switch between them by unplugging and plugging the devices in back and forth. Once in awhile I'd lose the keyboard when doing this, but usually not. Is there any reason why I lose my keyboard when switching on the KVM, but I don't lose it (as often) when I disconnect/reconnect the cable directly to the mobo's port?

    I might just get a new KVM as I'm still having resolution problems. Loads up fine when I'm in 800x600, but in 1024, the screen is still blurred. It's actually worse with the more expensive monitor cables. Unfortunately the pipe insulation didn't fix the problem either. Maybe it's just the KVM... I'll probably end up buying a new one anyways for the emulation. I need to be able to switch back and forth fairly easily. Hopefully this post is halfway coherent, as I'm about to fall asleep at the keyboard.

  10. #20
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    Get a 2 Port Cybex. You won't regret it. Are you familiar with ebay and how ebay works? If you know how to use ebay well, That is the cheapest place to get one.

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