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TI 99/4a Mitsumi rebuild to Cherry MX Style Mechanical Keyboard


Muldrf

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I recently came across a project to rebuild one of the failure prone Mitsumi keyboards into a new Cherry MX based keyboard.  The first 99/4a I purchased a few years ago had a failing Mitsumi keyboard in it.  I was happy to find this project.  He has a good guide on building it, and a youtube video going over it.  

 

https://github.com/visrealm/keyboard4a99

 

I did make a blog post about the build I did.  I did not track my expenses.  It was the cost of the PCBs, the Cherry MX compatible switches, and the latching switch for the Alpha Lock.  The other bits I already had in my stock of parts.

 

https://hobbytronics.home.blog/2024/09/29/ti-99-4a-mitsumi-to-cherry-mx-keyboard/

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12 hours ago, Muldrf said:

I recently came across a project to rebuild one of the failure prone Mitsumi keyboards into a new Cherry MX based keyboard.  The first 99/4a I purchased a few years ago had a failing Mitsumi keyboard in it.  I was happy to find this project.  He has a good guide on building it, and a youtube video going over it.  

 

https://github.com/visrealm/keyboard4a99

 

I did make a blog post about the build I did.  I did not track my expenses.  It was the cost of the PCBs, the Cherry MX compatible switches, and the latching switch for the Alpha Lock.  The other bits I already had in my stock of parts.

 

https://hobbytronics.home.blog/2024/09/29/ti-99-4a-mitsumi-to-cherry-mx-keyboard/

Yes, you can find some more about his build here:

 

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I designed the keyboard upgrade. Very nice and detailed blog post - thanks for sharing!

 

It's a shame about the key alignment. The switches not having alignment pins obviously didn't help but it looks like you did a great job to solder those in straight enough. I've taken another look at mine and there are very minor alignment issues, but not really noticeable unless you're looking for them. I share your opinion of the alpha lock key. It works, but a longer throw would be nicer. You can get locking cherry switches too, but they're super expensive.

 

Cheers

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10 hours ago, visrealm said:

I designed the keyboard upgrade. Very nice and detailed blog post - thanks for sharing!

 

It's a shame about the key alignment. The switches not having alignment pins obviously didn't help but it looks like you did a great job to solder those in straight enough. I've taken another look at mine and there are very minor alignment issues, but not really noticeable unless you're looking for them. I share your opinion of the alpha lock key. It works, but a longer throw would be nicer. You can get locking cherry switches too, but they're super expensive.

 

Cheers

I did look for a post on it, but couldn't find it last night.   I figured it should be on the forum somewhere.

Thanks for designing it.  The key switches are quite strait, in a perfect world I would have wanted the extra pins.  The large center post is a very good fit for the opening making them have a rotation at it, so that looking at the two metal pins from the top can give a good idea if it is strait or not (unless the metal pins are bent).  It wasn't too bad to keep the alignment close, although I had to adjust a few now and then. 

With how strait the Cherry Switches turned out, it was a bit disappointing having the keys twist on the adapters.  It isn't a design issue, it is just how the happened to print for me on my printer sliced as they were.  I was doing the keyboard from the Spacebar up, and didn't notice the more minor twisting as I was going, until I got to the P key, which meant most of it was together before I noticed it.  If I had seen it sooner, I may have stopped and done some tuning of the printer to reprint the adapters then.  I don't want to risk pulling all of those 3d printed adapters, the odds of some of them breaking off in keys is a bit too high.  I do plan to look at the Enter key this weekend though, and probably the P and a couple other keys.

 

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