Model F XT barrel codes

User avatar
Clavius
IBM aficionado

19 Jul 2017, 10:20

I've been happily typing away on a IBM model F XT 5155 (the portable personal computer one ;) ) for a while now, but yesterday evening my numpad 6 stopped registering. I took the assembly apart to investigate, and put a single flipper on the separated pcb. The 6 registered, so it doesnt seem there is a electrical problem.

Anyhow. Opening up the board was also a good opportunity to clean the barrel plate and barrels, which I didn't attempt during my initial cleaning. I took out the barrels and put them in a bucket with dental tabs, rinsed hem after a while and put them to dry. This morning I discovered something I hadn't noticed before; the barrels have different codes. And not just a few, but many different ones.
This would suggest that the barrels have a designated spot on the board, which I now completely mixed up. I've googled for an hour to find any 'map' how to place the barrels, or any mention of the issue, and didnt find anything.
The codes on the barrels don't seem to follow a logic order that would map the matrix (H10 could work, but GW makes no sense). At some point I thought maybe the code corresponds to the individual keys (e.g. AW, CW, GW would map to A,C,W), but for many codes there are duplicates (I counted four AW marked barrels).

I also compared a number of barrels with different numbers, and apart from the numbering they seem optically identical - no differences in curvature or barrel angle.

So, what am I dealing with here? Are the barrels simply interchangable but from different batches, placed on the board in a random order? Or is there some higher order to this chaos?
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User avatar
Chyros

19 Jul 2017, 13:05

Pretty sure the barrels are all interchangeable. IBM massively optimised and simplified their keyboard manufacturing structure.

Engicoder

19 Jul 2017, 13:18

Usually those codes are mold numbers. Due to high volumes, several sets of identical molds are used for the same part. In order to identify which mold an individual part came from, identifying numbers are added to the mold. These numbers are used for quality control and to determine when a mold needs to be replaced.

User avatar
Clavius
IBM aficionado

19 Jul 2017, 21:19

Thanks a lot guys, I've gone ahead and placed the barrels randomly, put the board together and everything is back to normal; typing on it now. Kind of curious to see how many molds there must have been.
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