HOWTO: Make an Avocent SwitchView KVM Switch Video-Only

Here's a tutorial on how to hack an Avocent SwitchView KVM switch to switch video-only (that is, switch video signals without a keyboard or mouse attached). If that seems puzzling, read the following description of the problem and why I felt it necessary to deny Avocent a hundred of my dollars. Or if you're ready to hack, just get right to it.

WARNING and DISCLAIMER This procedure is not for the technically faint of heart. It requires some basic soldering skills. If you blow it, you could kill your switchbox, or worse, yourself. So if you're not completely comfortable with the procedure described here, please refer this work to a professional or just spring for the PS-6F power supply for each port you want to switch video-only. I am not responsible if you mess up your KVM or suddenly feel drawn to a great white light (remember: run away from the light). Also, this procedure will definitely VOID YOUR WARRANTY.

But...Why?

I have two computers, each with two video cards. I have two monitors. I want to switch two monitors between two computers. Very simple: use two KVM switchboxes. One KVM switches keyboard, video, and mouse, the second KVM just switches the video for the second monitor.

Sounds simple enough. My employer has seen fit to provide me with as many Avocent (formery Cybex) SwitchView 4-port KVMs as I would like. They're fairly inexpensive and do a nice job of switching without introducing a lot of ugly video noise, and they have some nice keyboard shortcuts for direct access to a particular port, etc.

Most KVM switches leach power for the switch's circuitry from the computers to which they are connected. Conveniently, pin 4 of both the PS/2 keyboard cable and the PS/2 mouse cable provide a +5 VDC source from which to power the switch. So, when a KVM is just plugged into video, and not to any computer keyboard or mouse ports, where does the KVM get its operating current? Well, usually from an external wall wart transformer. That's why most KVMs have a 5-to-9 volt external power input, even though most of the time you don't need it.

So when I hooked up my Avocent SwitchView KVM to my second monitor and my two computers' second video cards, I wasn't really surprised that it didn't initially work. Of course, the KVM needs some juice. The manual says:

A little vague about which circumstances, but fair enough. I've got these kind of wall warts just sitting around, but if you don't, just go to Radio Shack and buy a 273-1761 6V 800 mA Power Adapter, and be sure to ask for a free 273-1705 "B" Adaptaplug (outside diameter of 4mm, an inside diameter of 1.7mm, and plug-type A=positive tip). The transformer will run you about $18 bucks.

So I got one of those, and plugged it in, and alas, my KVM still didn't switch video for me. Nothing. Just like it wasn't plugged in at all.

So I wrote a friendly email to Avocent Tech Support to find out what was going wrong. Here's the extent of the exchange.

This attractive PS-6F power supply lists for $49, per port. So what's that 6 VDC input on the back of the KVM for anyway? Certain unspecified circumstances, I guess.

This is an obvious money grab. It pisses me off when companies do things like this. For comparison, products like Linksys SVIEW04 KVMs have an external power input which does enable the device for video-only switching, and the wall wart is even included in the package! Horray for Linksys! Too bad my employer wants me to have Avocent KVMs.

It pissed me off enough that Avocent wanted me to buy $100 worth of wall warts to make a $80 KVM do what I want that I decided to hack it, and deny them their unsavory profits. Arg arg arg matey!

Let's Get Hacking

In short: we're going to directly wire pin 4 of the mouse inputs of two or more of the KVMs ports to the external power supply input.

You'll need:

• Your Avocent SwitchView KVM
• A small Phillips-head screwdriver
• Some small-gauge insulated hookup wire
• A soldering iron
• A nice static-controlled environment, like a big stat-bag
• A Radio Shack 273-1761 6V 800 mA Power Adapter with a 273-1705 "B" Adaptaplug (or equivalent)

Also, you should know in advance which ports you want to enable for video switching. For instance, if you're only going to hook up two computers, then only perform this modification for ports A and B, and leave the other two ports unmodified. This is because the switch will include all modified ports in the rotation that happens when you press the "Select" button, and you don't really want unconnected ports in that rotation.

1. Disassembly

Completely disconnect the SwitchView and turn it upside down on your stat bag or other static-controlled setup. Remove the two screws on the bottom. The device comes apart into five pieces: the top panel, the bottom, the faceplate, a backplate, and the circuit board itself.

2. Mod Preparation

Set the plastic enclosure panels aside. Turn the curcuit board over, so it is resting on all the connectors. On the right side of the board you'll see two pins from the external power input jack protruding through the bottom of the circuit board. The jack's pin is the positive voltage, and that's where we're going to get our power.

The leftmost set of K/V/M connectors is for computer A, and to its right are the connectors for computer B. For each block, the mouse port is the leftmost mini-DIN jack, and pin 4 comes through the board on the right (see the picture). Our job is to run a jumper wire between the positive power point noted above and each of these mouse pin-4s.

3. Wire It Up Remember you decided up front how many ports you were going to enable? Cut a jumper wire long enough to go from the power point to the mouse pin-4 for each port you want to enable, starting from The left (A, B, ...). Once you've got the jumpers all cut, strip 1/8" off each end of each jumper, bundle one end of each jumper together, and solder them all at once to the power point as shown in the picture (I only enabled two ports). Cut off any excess after the solder is cool.

Now, for each jumper, solder the other end to the mouse pin-4. I think this technique works if you attach to either the keyboard or mouse ports, but I only tested it with jumpers to the green mouse ports (use the picture for reference).

Your finished product should look something like this.

4. Test Time

Pick up the SwitchView (don't leave it on some possibly conductive surface). Get your 6 VDC wall wart, plug it into the wall, and then plug it into the extern power jack on the back of the SwitchView board. No need to plug anything else in for the test.

Nothing will immediately happen. Press the Select switch. The SwitchView should light up the orange LED for each enabled port in succession each time you press the Select button. It will skip any non-enabled (jumpered) port. If that works, happiness happiness!

5. Reassembly

Disconnect the wall wart power from the back of the SwitchView board. Put the backplate onto the back of the circuit board. Place the front panel into the slots on the bottom panel, then slide the circuit board into place behind the front panel. The backplate should then sit nicely in a little slot at the back of the bottom plate. Fit the top cover back on, aligning the backplate. Flip it over and replace the two screws.

Congratulations!

Enjoy your improved SwitchView!