A lot of the caps didn't match up in texture and profile, which I thought was kind of weird. That piqued my curiosity and I took a closer look. When taking the keyboard apart I noticed there were several other differences between those two boards. Almost like a generational gap. One is older and the one I bought after that is a lot younger.
Here are a few things that I noticed:
- The upper (plastic) case
IBM seems to have switched their process and/or materials in between generations. The older one seems to be made from the same plastic as the front panel of my PC Model 80. You can see where the big nozzle part was cut off. The material is more brittle and therefore thicker, which makes the case heavier. That influences the sound just enough to notice.
Also they had to use brass inserts for the four screws that hold the case together. Notice how the columns for those also are a lot thicker. On the newer one the screws go directly into the plastic and carve their own thread. The geometry (seen from the inside) also differs a little bit.
Spoiler:
- The bottom (metal) part of the housing
There are a small number of slight differences between the bottom plates. The cutout for the cable in the back seems to be a little wider. Don't have photos of that, unfortunately. The plate is at the paint shop getting powdercoated rn. On the front the newer generation has three teeth to help position the upper case. Probably because it doesn't have a step as pronounced as on the older one.
Spoiler:
- PCBs and Controllers
Not quite sure here, but the controllers sure look different. Not too shocking seeing that the older PCB looks like typical circuit boards from that time (in regards to material and the traces and so on). Connectors on the cables are also different.
Spoiler:
- The keycaps
First of all, they changed the font they used. You can see it when comparing the numblock keys to the numrow ones, where the legends are smaller. The new Q kinda sucks, ngl . These two "generations" also differ in shape quite a bit. The older ones have deeper dishes (most noticable on the homing keys) and IBM used different inserts for the molding process. The older ones are also a tiny bit higher and thicker at the top. The texture (so the grainy surface structure around the legend) seems to be rougher/more course on the older caps. Internal structure is also different. The new inserts are just the flat legends on a grid structure on some of the keys, like with Focus' Alps caps. On others they come down to the bottom corners but are stemless, and on very few of them, they are built like the older ones. On those the inserts reach all the way down to the bottom and contain the stem. Even the blank keys (on the 5251 left of numrow "1") are different. And I've even found an exception within the older keys: The "3" clearly has the font and shape of "Gen 1" but is built like a "Gen 2". All of this makes the older caps generally thicker and heavier. Most noticable on the left cluster of my 5251s. Lastly, the new ones don't seem to yellow, like at all. Maybe they changed up the formula on their plastic or used an entirely different one. Here are some more photos I took on the next day. Unfortunately, I mixed up the order, left is new here while the older ones are on the right.
Spoiler:
I'm sure people are already aware of this but I couldn't find anything specific about that, so I figured I'd open up a topic for people to share their experiences. I'd be happy to hear some confirmation for my findings, maybe even some more differences I missed on the 5251, or "generational differences" on other Beamer models.