I recently got a Fujitsu FKB 8738 in the mail. There is a seller on the Swedish auction site Tradera that sells them for 50 SEK + s/h. I read up on it, saw that it was a rubber dome (no surprise there) but
hey, it is tenkeyless and has a built-in trackpoint. I couldn't refuse.
Unfortunately, when I got it, I felt that the domes are
very mushy.
I opened it up, and found the rubber sheet. Hmm.. It expanded a bit after the buckling, which explained the mushiness.
Hmm ...
So, I looked through my box of old rubber dome keyboards ... and took out a Keytronic KT1000PS2SV -- in my opinion, the best of
all rubber dome keyboards. The donor keyboard was almost ten years old, with very shiny keycaps, plus it had AT layout.
I compared it to the Fujitsu keyboard's rubber sheet and looked for similarities and differences. I also had the sheet from a IBM rubber dome keyboard made by Chicony, but the domes on that sheet were too high.
Here is the keyboard with its old membrane:
Sorry about the pics. Old camera, no natural light.
The best thing was that the
Esc and
F-keys had what looked like identical locations on the sheet on the keyboards.
Unfortunately, I found a few minor differences: The left
Ctrl key is wider than the other modifiers on the bottom row, where the Keytronic's are the same size. Unlike the Keytronic, the
Caps Lock and
Backspace keys have centered switches. The location of right
Shift and
Enter key switches are also slightly different.
The spacing between the inverted T-cluster/nav keys is also bigger on the Fujitsu than on the Keytronic KT-1000, so this is what I started to cut up.
The relations between the Keytronic's
Enter and right
Space switches was the same as between the Fujitsu's
Backspace and
Enter keys, so I just cut and moved these switches up and to the left. The
Caps Lock key, I moved just a little bit to the right. I found that the distance between the left
Ctrl key and
Space bar was the same, so I kept the rubber sheet connected between these two and turned the left
Win/Alt keys 180º.
Most of the cutting, though, was making new holes in the sheet so that it fit..
I used a sharp hobby knife to cut the holes.. I had tried first to use hole punching pliers, but that did not work very well. It is not as easy to cut straight line in rubber as I thought that it would.
So how it is?
The key feel is very much improved. Far from as mushy as it was in the beginning. Bottoming out is dampened but distinct as on the the Keytronic. However, it is still a long way from the quality of the donor board. The new keyboard is more noisy. It both feels and sounds more "plasticky".
I made one stupid error: The Fujitsu has a curved back plane, while the KT-1000 is flat ... so the domes get a fraction of a mm more out of alignment and just a little bit more mushy at each higher row. This is not very noticeable except for the top row, but I rarely use the F-keys at all, and I think that I can do without them.
A big problem is making the domes stay in place when you reassemble the board. A few of the domes are a bit out of alignment - some keys are a bit mushy, others feel very tactile but a key press is harder to register.
I will have to find a way to glue pieces of the rubber sheet together again. Sticky tape does not work. I suspect that the rubber sheet is made of silicone. I will try to see if some moulding silicone that I have could be used as glue to mend the parts together again.
