KVM Overview

I have perhaps too many computers in my computer room. I access them all using a KVM switch. One issue I have found is some computers are a bit fussy about a USB keyboard and mouse. Some don't recognize them during the boot process, but only after booting is done. Some recent motherboards from 2009 have this problem. You can work around this by using a PS/2 keyboard, which I consider an ugly hack, especially since some of my computers rear panels are hard to access.

VGA Cables

What is worse, is many KVM video cables suck in a major way. One common problem I have found is many don't have a conductor for the plug and play signal. If your monitor isn't detected as a plug and play monitor, the problem is either it is more than 15 years old, or the KVM switch doesn't switch the signal (rare), or one of the VGA style video cables doesn't carry the signal. The data is on pin 15, and 5 volts is on pin 9. You can check for continuity on these pins, and if it is missing, your cable won't supply plug and play data. Another issue, is high resolution video works much better if the RGB video signals each are on their own coax cable. Cheap KVM cables with PS/2 connectors included rarely have coax inside of them for the RGB video signal. I recommend high quality cables that are advertised as having coax for the video. If you are running less than 1024 pixel wide displays, this isn't important, but my display is 1920 pixels wide, and it makes a huge difference.

Many people advertise high quality cables. Without lots of fancy test equipment, or taking the cable apart, it is pretty much impossible to tell the quality of the cable. Of course, if you hook it up and there is poor video quality, you can be pretty sure you have a crappy cable. Also it is very important that the cable connects all of th bins from one end to the other. There will be 15 signals running along the cable, which can make it a bit thick.

It turns out that although the Belkin Pro VGA cable has very nice video, it does not connect all of the pins from one end to the other. As a result, the EDID information that the monitor tells the computer never gets back to the computer, and trouble follows quite quickly.

Linksys makes a very good 4 foot long VGA KVM cable. The only downside to the Linksys cables I have is they are quite thick. Do not confuse thickness with quality. I thunk I will be migrating to a 4 port HDMI switches to augment my Belkin OmniView Pro2.

I just bought some Kaybles SVGA Cable Super Shield 10 foot cables. They were reasonably inexpensive. What is critical is the specs said "3 coaxial +4.5 twisted pair cable" The 4.5 twisted pairs means 9 conductors. Add in 6 conductors from the coax, and you have 15 conductors. I verified that the cable does support EDID (which the specs imply). The video quality is decent. The cable itself is a bit thick, but I can live with that. I tried emailing Kaybles. I sent at least 2 emails asking about the maximum resolution the cable supports. No answer. and calling them several times, but they never answered their phone.

I have had quite mixed results buying cables on ebay. The last cable I bought was sold by yellowknife_cable, a Canadian company. The title of the auction was "Ultra High Resolution Monitor Cable (Make VGA to Make VGA) - 10ft". The photo included in the ad state "All 15Pins Connected to Support LCD/HDTV". They are lying. This cable does not support EDID. When I complained and suggested perhaps they shipped the wrong cable, and I needed a cable with all 15 pins connected, they replied "not really understand what do you mean. the all 15 pins are there, you can see them by your eyes. And the cable was tested before shipment. Your monitor is plus-and-play or not, has nothing witth our cable. It is your problem." Well, I admit that the 15 pins are present, but some of them are not connected to anything except the body of the connector. They are not electrically connected to anything. Of course, I was testing with a known good notebook, a modern monitor, and comparing their cable with a known good cable. I can't speak to the resolution of their cable, but without the EDID, the cable is pretty much useless with a plug an play monitor, which has been a standard for well over a decade. Ebay refunded my money after I opened a dispute.

Belkin OmniView Pro2 8 port KVM switch

I decided I wanted more ports than my 4 port KVM switch, as I have 5 computers in a rack, and often test another computer. So I bought the Hawking switch, as it was inexpensive. Well, for some inexplicable reason, it didn't like the keyboard and mouse output of my Compaq notebook. The Zonet KVM switch liked it, so I suspected the problem was with the KVM switch. I decided it was time to buy a real KVM switch. I picked the Belkin. The only problem it has is the KVM cables are male-female, but all of my KVM cables are male-male. Fortunately, one can always buy cables... The OmniView is a serious KVM switch as it rack mounts (like the Hawking). Unlike the Hawking, it can be daisy chained with other Belkin KVM switches to switch as many as 16 different KVM switches. It also supports computers with either PS/2 or USB keyboards and mice. It also has an on screen display, which displays the port you are switching to, as well as allowing you to name the ports. Needless to say, it worked fine with my Compaq notebook, and my other computers. I think it is no longer made by Belkin, but they can be bought used for very little money.

Well after using the Pro2 for a while, I noticed that sometimes when switching to my Compaq notebook, either the keyboard, mouse, or both wouldn't work. I contacted Belkin and they said I shouldn't be using the PS/2 splitter, which old notebooks use. I removed the PS/2 splitter, and hooked up the USB port. Works great better, but still sometimes the computer gets confused. If I remove the USB cable and reseat it, everything is fine.

Yesterday I noticed my control key was not working on port 1. It worked on other ports, so I though that quite odd. This morning, more keys were acting oddly. The right control key was acting as a caps lock. Other keys on the bottom row were not working at all. This was only happening on one computer I had plugged into the KVM switch. I was using the USB output of the KVM switch and plugging that into my computers. I plugged in a PS/2 keyboard directly to my computer, and that worked fine. I took that keyboard and swapped it with the keyboard plugged into the KVM switch, but the same keyboard problems occurred. I booted into a different OS, but the keyboard problems continued. Finally, in desperation, I unplugged the USB cable on port 1 and used two PS/2 cables. Now the keyboard works fine (on all my computers). From this, I conclude that the Belkin KVM has separate PS/2 to USB converters for each port, and for port 1, the PS/2 to USB converter has failed. The KVM has a 5 year warranty, but mine is older than that. For now, it is a good thing that my computer has two PS/2 inputs for the keyboard and mouse and I still have some old PS/2 cables. It isn't worth buying a new KVM, but it is bothersome. It turned out that the USB port started working after I swapped the capacitors.

Fixing Belkin Omniview Pro2 8 port KVM switch

Slowly over time, my Belkin produced a worse and verse VGA signal. I thought it was bad cables, I though it was crappy VGA hardware on my computers. I was wrong. It was the electrolytic capacitors inside the Belkin Omniview Pro2. The good news, it is pretty straightforward to replace them. First read the Instructabler. I decided to replace all of the capacitors on both boards. (It turns out that Belkin used 105C capacitors, even though the KVM switch should never get very worm.) If you do that you will need the following 7) 100uf 25v capacitors, 4) 470uf 16v capacitors, 1) 2.2uf 50v capacitor. Taking the Onmiview apart is straightforward. Removing the circuit boards is straightforward. My board was soldered with some kind of higher than normal temperature solder. I suspect is is lead free solder. If you have a variable temperature soldering iron, turn it up until the solder freely melts. I tried a standard (old school) temperature regulated soldering iron, and it was marginal to use. Removing the capacitors is pretty easy. I found it quite difficult to remove the solder with solder wick. A friend with a really nice solder sucker and an adjust ale temperature soldering iron was able to easily remove the solder. I bought a bunch of really nice 105C capacitors on ebay. They are dirt cheap if you buy them from China, but they take awhile to ship. I found a source on the internet that said the 470uf caps were 10v. They are not. They are used before and after the linear voltage regulator on each board. 12v of DC from a wall wart is the input to the regulators. Clearly 10v won't do. I like the 105C capacitors because they should last longer than lower temperature ones. You could also use polymer caps, but that is likely overkill and they might not fit nicely in the circuit board due to possibly different lead spacing. Replacing the capacitors even fixed the USB port 1 problem that I was having. I measured all but 2 of the old capacitors and they measured within tolerance. I am not sure how they are going bad, and I am not sure which ones needed replacing. Since I can't measure a ESR or leakage, I decided to replace them all. Since my KVM switch is on 24x7, it was worth it, given the hassle of pulling all the cables and opening the KVM. The front panel is not held on very robustly. One side was loose when I got the KVM, and several really small plastic tabs just broke off when I was taking the KVM apart, perhaps due to age or being generally flimsy. I ended up wrapping 2 inch wide packing tape around the entire circumference of the front panel to hold it on.

Hawking CS168 KVM switch

I bought this 8 port KVM switch used. It has buttons to select each computer. It has 'hotkeys' to also select a computer. When I tried to select computer 1, it didn't work. I was able to use the up and down arrows to select different computers though. One of the computers I have is an old Compaq notebook. It has a single ps/2 port, which can accept a keyboard/mouse ps/2 splitter. The splitter works fine with my Zonet 4 port switch. It doesn't work with the Hawking switch, so I get a few seconds of mouse movement, then it stops. I tried 4 or 5 different ports and they all acted the same, broken way. I went back to my Zonet 4 port KVM switch. Perhaps there is something non-standard about the ps/2 splitter, but I suspect the problem lies with the Hawking KVM switch.

Zonet KVM3002 2 port KVM switch

I bought a KVM switch. They allow one keyboard/video/mouse to be shared between two computers. Some have manual switches to switch computers, some use keyboard shortcuts, some auto-detect. Doesn't sound very complex, but it would seem there are many things to go wrong.

I bought the Zonet KVM switch because it was cheap. I should have known better. If both of my computers were powered up, it worked fine. If only one (the ASUS CUR-DLS) was powered, it did not detect the keyboard. This is a bit of a problem, as the computer unusable. There is a place for external power for the KVM switch (the KVM switch draws some power from the PS/2 connector in order to operate). Zonet does not supply a power adapter. I hooked up one of the required power, but the switch still didn't work.

I contacted tech support. They told me they knew about the problem, and the rev B KVM switch would fix it. They told me I needed to fill out a RMA form and fax it to them along with a copy of the receipt. Since I don't have a fax, I asked if I could email it to them, and they said that was ok. I got a RMA number. I was told to mail in the unit, and they would mail out a new unit. I asked if they would cross-ship (as all civilized computer companies do like Adaptec, and APC to name a few) and they said they didn't do that. They also wanted me to pay for postage (some companies pay for return postage for defective equipment, like Gateway). I told them that I needed a KVM switch, as my computers were too far from the keyboard. I asked if I could drive down there, and they said ok. I drove there. I got a new, rev B KVM. I hooked it up. It was worse. It would only pass through about 1/3 of the keys of my keyboard. I tried with and without an external power supply. I have a Microsoft Natural Elite PS/2 keyboard, which is a very common keyboard. It did work with a cheapo Memorex keyboard I had handy.

The old KVM switch worked fine with my Microsoft keyboard, so clearly something in the rev B KVM had gone wrong. I called Zonet, and they told me they tested the old KVM switch, and said it worked. I told them they clearly didn't test with an ASUS CUR-DLS motherboard, as it didn't work that way. Zonet told me "I'll feedback this to the factory and hope they will have any fix for me. I'll keep you post." That was about 5 weeks ago. I heard nothing from them.

I sent them another email, asking for a working KVM switch, or my money back. I have heard nothing from them in about two weeks. I called them up. I spoke to tech support, and then to someone higher up. The higher up used a Microsoft Natural Keyboard, and wanted to get to the bottom of the problem. He brought his in, and tested it with the KVM products. It worked. So the next step is for me to drive down there, with my KVM switch and my keyboard and see what is going on. This is pretty dedicated support, except that it is a long drive for me. Hopefully it will resolve the problem. I can even leave the keyboard with them if needed, as I have a spare. We shall see...

I drove down there today with my keyboard, mouse, and KVM switch. After awhile, the tech was able to replicate my problem. Their Microsoft natural keyboard worked fine. The problem of most keys not working doesn't exist with their rev-A KVM switch, but does exist with the new rev-B KVM switch. Their new 2 port KVM switch that also switches audio has the same problem. I suggested they try their 4 port KVM switch. The 4 port switch works fine. I loaned them my keyboard, and they traded my 2 port switch for a 4 port switch (though I only have the KVM cables from my 2 port switch, so I won't benefit from the 4 port switch). They said they would send the keyboard to the factory to figure out what it is doing, and then send it back to me. The video quality seems better with the 4 port switch than the 2 port switch.

So I cannot recommend Zonet KVM switches, except the 4 port version. Their tech support is very hard to reach, and had a hard time fixing problems. Their testing of their products is clearly substandard. Needless to say, I won't be buying any more Zonet products. I would have never thought that so many things could go wrong with a KVM switch design.

Zonet KVM3004 4 port KVM switch

I have been using the 4 port Zonet KVM switch without any problems for a few years. Then I decided to install Windows 7 on one of my computers. I had always had to specify the type of monitor I was using when installing any OS on any of my computers. I though that was just how it was done. Then with Windows 7, I didn't have a 'driver' for my Dell 2405 monitor. Dell said that it was a plug and play monitor, and it should work fine with Windows 7. Well, it wasn't for me. It turns out that the 'plug-and-play' signal goes through some wires in the VGA (or DVI) cable. I thought the problem was my KVM switch. Everything worked fine when I just used an extension VGA cable. I tried several KVM switches, and every one failed to send the 'plug-and-play' signal, which is really part of the Display Data Channel (DDC) signal that modern monitors (that means less than 10 years old) supports. After much thrashing around (and 3 KVM switches and a DVI cable), it turns out that the Zonet KVM switch was just fine. The cables I had from a cheap KVM switch were not passing the DDC signal. The two cables from my old Zonet KVM3002 KVM switch however worked fine, and did pass along the DDC signal.Unfortunately, I have only two of these cables lying around.

If you have comments or suggestions, Email me at turbo-www@weasel.com

Created with gnu emacs and template-toolkit, not some sissy HTML editor.

No Java or javascript needed to view my web pages. They both have significant security issues.

Home