PC-1600 [mitsumi KCM, probably]

User avatar
zrrion

09 Feb 2022, 07:09

MIstumi has a bad rap around here and it's only like half deserved. KAM (mitsumi type 1) is a perfectly cromulent switch very much on par with SKCC IMO. Mitsumi's later offerings may/may not be deserving of hate but I don't have a lot of experience with them.

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long left shift, alt is moved to the left of the spacebar, numpad + is reduced in size to make way for a more useful key, and the enter is a medium-ass enter. In addition to all that long bracket isn't present and to compensate the entire alpha cluster is shortened slightly which doesn't really do anything to make the thing better but it's a neat detail. To prevent the right shift from getting shortened by the alpha-shortening they move the prt sc key down to the bottom row but that's fine honestly, means they didn't need multiple shift molds. This is for sure the most usable XT layout board I've even used.
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proof that at least part of this was made by mitsumi, whether the entire keyboard module was or not I don't know.
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interesting that there's a place ofr a speaker here even though the pads for the beeper are on the the side of the PCB. Other versions of this board don't even have a beeper (or NKRO for that matter) so why this case has the "speaker grill" all the way over here is a mystery. Even though the pads for the beeper are unpopulated the thing does beep if you install a beeper. I tested this out with a small speaker since I couldn't find any of my beepers but it does actually work and once I find my beeper stash I'll put one in as well as poke an off switch out the back or somewhere.
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This dummy switch kinda sucks. It works as a stabilizer but it makes the enter key feel weird and especially now that I've lubed it the thing is a little sluggish. I'll eventually get a very light spring into the dummy switch but for now it's fine.

This keyboard is my only point of reference for DIN-compliant mitsumi switches and it's a mixed bag I guess. The keycaps are really good, they're thick, the legends look nice, and they sound nice, the board itself had NKRO and the layout solves basically every complaint I have with XT while still being unmistakably XT. On the other hand tops of the caps are way too wide and it makes typing on them weird, the switches aren't especially smooth and cleaning/lube hasn't improved them as much as I thought it would.

It was pretty dirty when I got it, all the keyboards from this seller have like dust ingress of the same sort so I kinda expected that. Was looking forward to seeing how these switches responded to waxboil so it's whatever.

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Contrary to what some people would have you believe, waxboil is easy as 1-2-3. I boiled the bottom housings, top housings, and sliders in different batches, a few minutes of boil like you see in the pic. A strong boil like pictured is required and it makes stirring unnecessary which is what you want. I set the housings to the side to dry and changed out the water for the sliders. To the new water I added my wax, let that get to a decent boil because I got distracted peeling the stickers off of the caps. IDK why it had stickers as there weren't legends on them. I set the sliders aside to dry with the other parts and when they dried I did a test of a single loose switch to see how it was and while it wasn't anywhere near as bindy as before it was still just as rough. I lubed the slider channels in the bottom housing with dielectric bulb grease and that helped a lot with the feel. but even with lube that thick they still feel a little rough and you can still hear the roughness. I have a high tolerance for this sort of feeling and sound they would liekly drive an MX switch modder up the walls. I tried lubing the places where the top housing and slider meet but that doesn't have a consistent effect and neither did lubing the contact leaf so I didn't bother doing it to every switch. they're livable as they are now, which is more than could be said about the switches when I bought them so I'm calling it a win.

here's some pictures of the switch internals for anyone who is wondering:
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standard switch, the spacebar switch was the same but with a heavier spring and different coloured slider/housing. As I understand it the black housings are smoother than the milky ones. my limited experience with the black housings (3 switches on this board) that does seem to be true but I admittedly have a small sample size.
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and the LED switch. Like KAM LED switches they have almost everything they need to become latching switches except for a few latch parts.
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and these motherfuckers are the worst. They're the clips that hold the stabs to the plate and they break if you so much as breath at them. I managed to glue them back together but it was dangerously close to getting glue on the stab wires and I don't trust them to not fail on me if I look at them later. Fuck these stabilizers.
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that's not dirty, it just has a little bit of black plastic mixed in.
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and here's the back of the dummy switch from the enter key. the missing corner is not damage, but rather an intentional adjustment of the switch to allow clearance for a diode that would otherwise be in the way.

and an after pic after all the cleaning was done:
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and the label on the back.
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no FCCid though so I can't look up who is responsible for this keyboard.
Last edited by zrrion on 04 Apr 2022, 03:32, edited 1 time in total.

User avatar
zrrion

09 Feb 2022, 07:26

2nd post for explaining my reason for calling these KCM, starting with a rundown on the naming conventions for mitsumi that I stole from Manbdarbmax because I feel like this info is useful on its own.

Mitsumi switches have a 3 letter designation and the first letter denotes the type of switch. For keyboards it'll always be K.
The 2nd letter denotes the series. A is type 1 (possibly for all their pre-din switches?), B for PCB switchplate (has a similar contact setup to ALPS spring bridge where a PCB is used for the contacts and sticks out of the bottom of the switch), C for type II, D for simplified, L for Minimech, K for hybrid mechanical over PCB, P for hybrid mechanical over membrane.
And the 3rd letter is for the subtype. M is for linear (or rather momentary), T is tactile, R is hybrid mechanical progressive linear, Q for hybrid mechanical buckling rubber sleeves.

So these switches are K for keyboard, C for type 2, and M for linear giving us for KCM. This makes sense and I can't think of any other things it could be but there's no official source on this so there's always the possibility that these are some weird exception or something. This board also has the same switches but from what I can tell there's no indication of what they are in those pictures

User avatar
zrrion

10 Feb 2022, 02:08

Here's a typing demo: https://freesound.org/people/zrrion_the ... ds/618596/
It takes a while for freesound to approve uploads but it will show up at that link with details on the sound's license, if you can't wait that long there's a direct link to a lower quality version here

Rhododendron

10 Feb 2022, 08:30

Quite an interesting board. And very good documentation on your end!

User avatar
zrrion

16 Feb 2022, 20:42

Just got a beeper wired into this thing and unfortunately it will repeatedly beep when a key is held down, which is super annoying. I haven't discovered a key combo for toggling the beeper so far so I'll probably just add a switch and poke that out of a hole in the case or something. I'll see about getting a demo with the beeper here before too long. The beeper I'm using is comically small compared to what the board appears designed for but the sound is nice enough.

EDIT: the board makes a different beep on make/break which is kinda neat and the break noise is different when numlock (in this case that's the keyboard state not the actual numlock) is enabled. caps lock does not appear to have anything to do with the sound and scroll lock doesn't effect it either. Additionally the break noise when the numlock light is different for the numpad numbers, so there are 6 tones, the standard make/break, numpad enabled make/break, and numpad enabled make/break for only the numpad numbers.

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zrrion

04 Apr 2022, 03:19

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picture of a normal keycap compared to these caps

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Polecat

04 Apr 2022, 03:48

Interesting, thanks for sharing! I believe this was also sold as a Monterey/Staff K7S. <attached, not my photos> I had one of these many years ago. Monterey K8S and K8XT are also related.
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box is not for this keyboard
box is not for this keyboard
k7slabel.jpg (308.36 KiB) Viewed 1753 times

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