Gefen DVI DL: Dual Link DVI + USB KVM

Once More, with a DVI Detective

As we mentioned before, Gefen's DVI Detective is a programmable box that will record your monitors EDID information and, once recorded, will continually transmit it to the host machine to trick it into thinking that the monitor is still present.

We purchased two DVI Detectives from Gefen, at a hefty price of $79.99 a piece. Although, in theory. just one would have sufficed as the only system exhibiting problems was the G5. Each DVI Detective comes with a DVI cable (you have to specify in your order if you want a dual link DVI cable) and a power adapter.

The DVI Detective is extremely simple in operation. You first hook your monitor up to the DVI In port on the Detective. Then, apply power to the unit and wait for the red LED to stop blinking. Once the LED has stopped blinking, the DVI Detective is programmed and you can remove power from the unit. Once programmed, the Detective no longer needs power to operate, so you can toss the power adapter in the closet until the next time that you need to program it (which should normally be the next time that you get a new monitor).

The DVI Detective has rubber feet to prevent it from sliding around your desk.

We programmed both DVI Detectives to the EDID signal of the Cinema Display, and then connected them in-line with the DVI DL KVM. It is very important that you maintain very good connections between all of the DVI ports in the setup, as we found that a loose connection can quite often be the cause of very visible artifacts on the screen.

Luckily, the DVI Detectives solved our OS X problem - now OS X stopped thinking that the monitor was unplugged every time that we switched away from the G5, and we stopped getting screen corruption upon the switch back. Also, with the presence of a DVI Detective on both machines, you no longer have to switch to the machine before starting it up. You can boot both machines without switching to either one, and still have full access as soon as you switch over.

The DVI Detectives also fixed the Cinema Display's USB hub problem. Now we could plug the hub into the DVI DL and switch between systems without losing keyboard/mouse support when switching back to OS X.

Unfortunately, our problems weren't over.

The inclusion of the DVI Detectives meant that we had one extra DVI cable per computer. In other words, the length that the DVI signals had to travel had just gone up by one more cable length. This translated into noticeable visual artifacts on the screen, individual pixels, or often times lines of pixels flickering would be the result.

Fine tuning the EQ knob would always get rid of the flickering, but what we found was that they would return depending on what we had on the screen at the time. The biggest culprit appeared to be playing a DVD. As soon as we'd start up a DVD, we would see many more flickering pixels than before. Part of it was due to the fact that the flickering pixels were more visible on black backgrounds, but once we adjusted the EQ knob to fix the issue on the DVD playback screen, it would return as soon as we stopped playing a DVD. The same applied to various other tasks that we performed on the computer, mostly involving the use of different colors than with what we adjusted the EQ knob originally. The end result was that we could never obtain an artifact-free picture with the DVI DL.

Naturally, we asked Gefen about the problem, and once more, Gefen was very quick to respond - although we weren't happy with their response. Apparently, this is a known problem with the DVI DL, and the engineers at Gefen are working on an auto-EQ that will constantly vary the EQ knob settings in order to fix this problem in all environments. Unfortunately, there is no ETA on the fix, nor is it known whether or not the fix can be retrofitted to current DVI DL units. Should the fix only require a firmware update, Gefen will add the fix to current DVI DL units under warranty. If it is a more substantial upgrade, however, current DVI DL users will have to simply purchase a new unit. To their credit, Gefen offered to refund our money after we asked them about the issue.