As described in another post, I’m using a Compaq Presario CDS 520 as a MS DOS gaming machine. I bought it in almost perfect condition from Swedish eBay, except for a broken “right arrow” key on the keyboard. In this post I will describe how to fix that.
First, separate the top and bottom of the keyboard by removing the three marked screws below. As seen, this keyboard is manufactured by Mitsumi, in September of 1994.
Now, disattach the controller board by removing the two screws below.
Remove the back plate of the large PCB by carefully loosening the black plastic snaps.
Now, it is possible to identify the problem by studying how the keys work. A key essentially consist of two parts: the key itself (with a rubber piece underneath), and a white piece of plastic with a conductive foot, which makes connects two parts of the pcb when the key is pressed. As seen in the images below, in this case, the pcb is dirty (and a bit worn). By cleaning the pcb and the key mechanism, it can once again make contact. In fact, this is a good time to thoroughly clean the whole keyboard from dust and stains!
If the black connective spots on the pcb would be subject to further wear, I suppose they could be fixed with a pen containing conductive silver/lead or similar.