4-Port USB KVM Switch DKVM-4U is a device that allows you to control up to 4 PCs using only one monitor, keyboard and mouse. The DKVM-4U is designed to allow you to control up to 4 computers from a single keyboard, monitor and mouse, so you don’t have to purchase a monitor, keyboard and mouse for each PC. The monitor and the two input devices (normally mouse and keyboard) are connected directly to this KVM switch. You can switch quickly between the individual client computers by pushing a button on the DKVM-4U or by pressing the hot keys on your keyboard. CAPS LOCK, NUM LOCK and SCROLL LOCK key’s status for each computer is automatically recalled. The manufacturer says that the DKVM-4U is capable of supporting the most demanding resolutions (VGA, SVGA and Multisync monitors) of up to 2048 x 1536 at 75Hz refresh rate (bandwidth up to 400MHz) without any noticeable degradation in image quality.
I found one slightly abused looking KVM switch that was thrown out either because it was broken or VGA monitor connections were considered obsolete. Manufacturer says this is End of Life products.
Let’s look what is inside. The case could be easily opened by removing the two ends of the case (just clipped on, no screws).
Here is the main board of the KVM switch.
When looking the chips on the board, I saw for example the following chips: two 74HC4052, two 74HC244, few CY7C63743, etc..
It seems that the RGB video signal switching is made with 74HC4052 Dual 4-channel analog multiplexer/demultiplexer that can handle up to +-5V analog signals with 60-80 ohms ON resistance.
CY7C63743 is USB interface microcontroller chip.