Reason for mat?

[klikkyklik]

I restored a keyboard recently that had a paper mat under the keys. What is the purpose of this mat? Is it just to keep gunk out of the PCB, protect against accidental fluid spills, or... any thoughts?

[Muirium]

I've seen these in various old non-IBM boards. Flimsy mats that are shaped like a plate would be, but the keyboard itself is PCB mount. I don't know what they're for. They sure are dust magnets!

Perhaps some nonsense to do with radiation emission standards. Bare components could have been frowned upon by the regulators.

[kbdfr]

[…] They sure are dust magnets! […]

That would be a good reason for such a mat: keeping dust from the switches

[seebart]

Something like this would make sense on dust prone Alps keyboards.

[Muirium]

Uh huh? But the switches are exposed through the holes, just like a plate. The boards I've found these in had very dusty switches too.

[seebart]

Right, so it`s a somewhat pointless measure. Must have some other reason then. Shielding? I don`t think so.

[Muirium]

As I said:

Perhaps some nonsense to do with radiation emission standards. Bare components could have been frowned upon by the regulators.

A lot of engineering isn't to satisfy scientific objectives, but is there to perform legally required hocus pocus. Sad but true.

[KRKS]

Either that or just noise reduction.

[Findecanor]

I think that it is there as fakery, to make it look as if there is a plate when in fact there is none.

Judging by the use of clone switches and not genuine Cherry MX, I would think that this was a relatively cheap keyboard to start with.

[Muirium]

Ah, noise reduction is possibly the reason. It's always soft stuff.

I've seen these on Mitsumi miniature switch equipped Chicony boards, which are definitely not MX clones, and are so light there's clearly no metal plate. I don't think it's subterfuge. Who would have cared anyway?

[klikkyklik]

I think that it is there as fakery, to make it look as if there is a plate when in fact there is none.

Judging by the use of clone switches and not genuine Cherry MX, I would think that this was a relatively cheap keyboard to start with.

Yeah, maybe just an appearance thing...

[Muirium]

Well, if "looks like hair and fluff stuck on shit" is your thing, then they sure are pretty!

I've tried cleaning them. Didn't go well. Too weak to bear the firm scrubbing required to release all the spooge. No loss. The keyboard works just as well without.

[klikkyklik]

Well, if "looks like hair and fluff stuck on shit" is your thing, then they sure are pretty!

I've tried cleaning them. Didn't go well. Too weak to bear the firm scrubbing required to release all the spooge. No loss. The keyboard works just as well without.

That was my conclusion as well; after removal and the board cleaned up, the mat didn't go back in. I still have it, but can't see a use for it (hence this thread).

Thanks for the responses, guys. I'll chalk this up to "who knows?"