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Nelno

Hi-Tek 373-70229A Keyboard Disassembly

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See attached pictures.

 

The 2 key on my TI-99/4A keyboard is sticky, and the 1, 2 and 3 keys have cracked rectangular white "thingies" that hold the keys (I couldn't come up with a good term for these). I'd like to see about fixing the 2 key's travel and possibly 3D-printing replacements for the 3 key "thingies" (though I think it will be tricky-bordering-on-impossible for my printer to print at that precision).


My keyboard's PCB is marked as HI-TEK and I've found some info on it here and here, though mind is 373-70229A and I've only found examples of 373-70229B. The closest example I have found here on AtariAge is in this thread, but it's just posted as an example and not discussed. Mine appears to be the same, only the top side of the PCB is a beige color instead of green like that picture. 

 

The main question I have is, is there no way to get the PCB off the back without de-soldering each of the key switches? 

 

There were 9 screws in the back of the PCB but removing them makes no difference. As far as I can tell they didn't need to be there at all. So either something is just very stuck -- I'm worried there may be some glue involved -- or I really do have to de-solder everything for this particular make of keyboard. I'd rather not have to de-solder 47 x 2 or so places on the board and risk damaging it or just finding out that there's some glue holding it together.

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This did indeed require de-soldering 94-odd pins in the back. I wouldn't recommend this unless you own a de-soldering gun. With the de-soldering gun it was easy and the board then came right off the back.

 

Starting here, I was able to find an old reference manual for a CDC IST II which also used Hi-Tek "Hi Profile" key switches which said to basically just grab the white "plunger" (aka "thingie") with some long-nose pliers and pull up to remove it. Well, that didn't work.

 

Instead, I was able to use some needle-nose pliers to pinch the outside bottom of the plunger from the other side to compress the two nubs on it side and then pull it out.

 

Take care after de-soldering the PCB, since all of the contacts are sticking out of the back of the keyboard "waffle" housing after the board is removed. It would be easy to bend or break them off when working with the keyboard. 

 

The de-soldered board:

 

20201216_185839.thumb.jpg.04aac20fdb23502459d2ccfb021b5800.jpg

 

The "waffle" housing after the board is removed:

 

20201216_185915.thumb.jpg.d13f6f45588e721bbd6a10729131d3e0.jpg

 

The removed plunger and spring on the back of the "waffle" housing:

 

20201216_194024.thumb.jpg.bd5d7267865befa67674ab5a5f37061f.jpg

 

The front of the "waffle" housing:

 

20201216_194306.thumb.jpg.f569952e241cc7e8067050802397f8c1.jpg

 

After getting the plunger out I am fairly confident I can 3D print replacements.

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I'd like to see how the 3d printing works out for you.  I have the same keyboard, while it is all working, several of the stems there are cracked.  It is apparently a common thing on them being thin like that.

 

They can be pulled out from the top with some pliers that have a bit of a grip on them.  Anything smooth metal only will slip, but ones with the little ridges can be used to pull them. Still they are quite secure or at least the ones I tried. I don't know that I would try pulling them with the pcb removed.  I figure they give that instruction, because it is expected to be a common failure, and not generally worthwhile to desolder the whole keyboard for one or two cracked stems.  I debated that just to clean up mine due to some issues with it, but I don't have a desoldering gun type iron.  The manual one I have works well for smaller tasks, I just wasn't up to using it for that many solder points.  I had looked into them and seen a video that went over repairing Stackpole keyboards, which these are.  There are two variations at least with the stems the one you have is the same as mine.  I did pull one of the cracked ones out to inspect it, and see if it really did pull out and find what variation I had.

Edited by Markeno
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16 minutes ago, Markeno said:

I'd like to see how the 3d printing works out for you.  I have the same keyboard, while it is all working, several of the stems there are cracked.  It is apparently a common thing on them being thin like that.

I will let you know how it goes. The biggest unknown is if I can get the wall width just right, as the tolerances are going to be pretty tight for my cheap printer. I can do some quick test prints of just the hollow rectangular part to see.

 

I suspect I could get these printed online from a place like Xometry.com with good enough resolution, but that might turn out to be relatively expensive.

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I've created this 3D printable version of the plunger. An initial test print for sizing was promising, but I'll probably need another couple of passes to get all of the tolerances right, and my guess is each one will need sanding so the operation will be smooth.

 

20201217_020623.thumb.jpg.b80e030873a2264e0446d8e81d32c83e.jpg

 

Also not sure that the PLA I'm using will be strong enough. My second prototype snapped at the bottom as I was testing the key fit. The original looks like it may be nylon and has slots in each side on the bottom but I'm not entirely sure all of those are necessary. I think they may be there to allow the piece to compress more easily when it's inserted.

 

Ignore the burring... it's slightly brutalized by me having to pull it out of the keyboard slot with pliers. It's only very slightly too large, nothing some sanding won't fix. And it's purple because I didn't feel like changing my filament.

 

20201217_021155.thumb.jpg.e1d13f918fb63f7c140cf092aa2b65c3.jpg

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Unfortunately after sanding down my latest piece to where it was fitting nicely, I tried to insert it without making sure the metal contact had separated and I crushed one side of the two copper contacts, breaking off the small pins there. 

 

I had tested this previously and the contacts were being pushed aside by the internal bar. However, it turns out that I put the nubs on the wrong side of the plunger I designed and when I aligned the nubs correctly on the outside for inserstion, I didn't realize the internal bar was 90 degrees off and it crushed the contacts.

 

This is a very minor fix to the 3D CAD design, but a major setback for my keyboard repair.

 

I am really, really bummed about this. Nothing like breaking a nigh-irreplaceable 40-year old piece of hardware to ruin your day.


There doesn't seem to be any easy way to get the broken contact out of the plastic waffle housing and finding (or making) a replacement seems like it's going to be rather difficult. I'm pretty unhappy about this, but at least (I think) the 3D printed plunger has a good chance of success.

 

20201217_175858.thumb.jpg.23c34c3642522dfeb7b591ce3837a805.jpg20201217_175911.thumb.jpg.34f1365556ead391f541179879a3f6da.jpg

 

Hard to tell from the picture, but that bar is going the wrong way compared to the little nubs that allow the plunger to snap in, and that's basically how I managed to break my contact on my 2 key.

 

20201217_180005.thumb.jpg.60a0c6b43c93f3531a94e144846ce6f5.jpg

 

 

Edited by Nelno
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1 hour ago, Markeno said:

Sorry to hear about the contact getting damaged. I hope you can sort it out somehow.

I was able to get the copper contacts out, one of them whole, and I think these can be fabricated by hand with a little patience, so that's what I'm going to try next.

 

I was able to get my printed piece installed into the keyboard, with spring, and I think it will work. Unfortunately it takes a fair bit of sanding and scraping with an X-Acto knife to get it to fit perfectly - my printer tolerances just aren't good enough to print something at this precision. I'm tempted to try Xometry.com but the turn-around on that will be a week or so minimum and I don't know for *sure* if the model tolerances are correct and the extra I'm having to take off is just due to my printer's low precision. Something printed professionally might just work from the model I have.

 

Once I've done a little more prototyping on my other keys with broken plungers, I'll be happy to print you a couple of replacements and send them if you want to PM me your address. I can do some basic cleanup on them, but you'll probably have to do some additional work to get them to fit your own keyboard and keys exactly. They seem like they'll be durable enough.

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Yeah, those copper fingers are brittle. I snapped off one on one of my keyboards as well. Never tried to fix it though; I just dropped it in my parts bin. I've considered replacing it with a standard switch for that key though.

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6 hours ago, fimbulvetr said:

Yeah, those copper fingers are brittle. I snapped off one on one of my keyboards as well. Never tried to fix it though; I just dropped it in my parts bin. I've considered replacing it with a standard switch for that key though.

Yeah, I noticed they were brittle even before snapping one. I was trying to be very careful with the contacts on the back that I had de-soldered, because they bend easily and once the PCB is off, they're very easy to hit accidentally.


However, once I figured out how to remove one (there's just a small tag on the copper that you can push in from the underside while pulling from the top) I measured it at 0.16 mm thickness. It's easy to find 0.15 mm thick copper sheets and they should do the trick. 0.15 vs 0.16 may change the feel of the key slightly, but it's much harder to get 0.16 mm (34 gauge) copper than it is to get 0.15 mm so that's what I have on order.

Edited by Nelno

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Just now, fimbulvetr said:

It will be interesting to see how that works out!


After breaking the contact I did start to look at how I could replace the entire keyboard with standard switches, going as far as measuring everything and getting specs on some Kaihl switches. I'm confident that I could 3D print a waffle structure to go on the PCB and that the switches could be mounted to match the height of the originals. They are significantly shorter (around 10 mm compared to 25 for the TI keys) and smaller horizontally / vertically, but it would require some additional wiring for every single key because the standard switches of today don't have their contacts right in the middle like these Hi-Tek switches do. In addition, some sort of adapter would have to be printed for every TI key to attach it to the top of a standard switch. It looks like that would all be doable and it would be pretty cool to have a keyboard that looked 100% TI but was using more modern switches.

 

I'm still thinking about this, but I suspect it would be at least a couple of weeks of work, on and off. I'd also have to order a bunch of switches to experiment on and I wasn't able to find a good source for those yet that wasn't overpriced and allowed me to get some reaosnable number.

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Interesting exercise. These days you could design a new pcb layout that fit the new switch pin spacing and have it made by Oshpark.

 

Too bad it seems the only source for one of the "good" TI keyboards these days is another console that happens to have a working one.

 

Ages ago I made a homebuilt wood case for a standard TI keyboard, connected to the console by a ribbon wire extender. It was very handy having a compact keyboard separate from the console. It had room on the right for a planned accessory keypad using double pole switches to add Function+Key for the arrow keys, edit, erase and so forth. Even ordered the DPST momentary mini switches, but that's as far as I got on the project. That console got stored away for some reason I forget. Still think about it from time to time. Maybe someday I'll come across the keyboard and stash of switches and wake that project up again.

 

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The 99/4a I got recently has a Mitsumi membrane type keyboard.  The membranes fail, which mine is almost functional but not usable.  So I got another 99/4a with the Hi-tek Stackpole keyboard.  Like Ed said, today the primary source of a working keyboard is to find another 99 to get a working keyboard...  I don't know what kind of keyboard the beige 99/4a I had decades ago was as it is long gone now.

 

I was looking at trying to repair or rebuild the Mitsumi.  I was looking at the possibility to use microswitches like smd Alps ones above.  I think that keyboard is a better option for such a conversion with the microswitches like that.  It is built a fair bit like Commodore 64 Mitsumi keyboards with the plunger design.  The keycaps are different, having a Plus shape to the contact, similar to Commodore 64 keycaps, but a different size.  As long as the Hi-tek is working well I don't have to rebuild it though.

 

If you would be up to sending me the file, I could try printing the part on my printer.  I doubt it is higher resolution.  I had seen reference that people have done it, and that it does take a good bit of sanding etc to make them work.

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On 12/17/2020 at 4:09 PM, Nelno said:

Unfortunately after sanding down my latest piece to where it was fitting nicely, I tried to insert it without making sure the metal contact had separated and I crushed one side of the two copper contacts, breaking off the small pins there. 

 

I had tested this previously and the contacts were being pushed aside by the internal bar. However, it turns out that I put the nubs on the wrong side of the plunger I designed and when I aligned the nubs correctly on the outside for inserstion, I didn't realize the internal bar was 90 degrees off and it crushed the contacts.

 

This is a very minor fix to the 3D CAD design, but a major setback for my keyboard repair.

 

I am really, really bummed about this. Nothing like breaking a nigh-irreplaceable 40-year old piece of hardware to ruin your day.


There doesn't seem to be any easy way to get the broken contact out of the plastic waffle housing and finding (or making) a replacement seems like it's going to be rather difficult. I'm pretty unhappy about this, but at least (I think) the 3D printed plunger has a good chance of success.

 

20201217_175858.thumb.jpg.23c34c3642522dfeb7b591ce3837a805.jpg20201217_175911.thumb.jpg.34f1365556ead391f541179879a3f6da.jpg

 

Hard to tell from the picture, but that bar is going the wrong way compared to the little nubs that allow the plunger to snap in, and that's basically how I managed to break my contact on my 2 key.

 

20201217_180005.thumb.jpg.60a0c6b43c93f3531a94e144846ce6f5.jpg

 

 

I'd be very interested in getting some of the plastic plunger replacements when you get things worked out to your satisfaction.  I have the same issue with one of my good consoles with cracked posts that cause the keys to stick.

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10 hours ago, FALCOR4 said:

I'd be very interested in getting some of the plastic plunger replacements when you get things worked out to your satisfaction.  I have the same issue with one of my good consoles with cracked posts that cause the keys to stick.

The main issue I'm having is that FDM printing just isn't precise enough to do this without a lot of cleanup on the parts afterward. The tolerance is about 0.2 mm and the width of the plunger walls is 0.6 mm. Both the inside and outside diameters of the plunger are important. Too small or large on the inside and the key won't fit or won't stay in the plunger. Too small or large on the outside and the plunger will be wiggly or stick. 


After having a bunch of failures with what is apparently some inferior gray PLA filament I switch to the other day, I've gone back to printing with white and I was able to get a piece sanded and working tonight. Unfortunately this is as small / thin as I can go with the piece before I start seeing artifacts in the print and this was maybe 10 minutes of shaving / sanding to get this piece fitting. In the pictures / video, I've replaced the cracked 1 key with the newly printed part. If you listen closely to the video you can hear the difference in the new plunger vs. the old. I think there are a couple of reasons: outside could still use a little sanding / smoothing, but it's close; inner bar is a little wider than the original so it has more friction on the copper contacts; I didn't do much, if any, cleaning on the lower inner cavity that holds the spring and I think that the spring is scraping on some of the imperfections I left there.

I will continue making minor adjustments to the CAD file, but and upload that here for others to use. Ideally this should probably be printed in nylon so it's not quite as rigid, but my printer only gets to 240C which is the bare minimum for nylon. With the CAD file it's possible to also get injection molded pieces done, but the minimum batch I've found for those is 50 and I didn't follow through with getting a full quote on what that would cost.

I probably should move this into the development sub-forum at this point. I didn't plan on making a whole new piece when I was starting on disassembling the piece.

20201221_014149.jpg

20201221_014234.jpg

Edited by Nelno
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Do you think it would help using a smaller diameter nozzle? I’ve had some success at the expense of speed using small diameter nozzle on thin walls.

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10 hours ago, DuaneAL said:

Do you think it would help using a smaller diameter nozzle? I’ve had some success at the expense of speed using small diameter nozzle on thin walls.

It might, but my printer isn't very modifiable in that respect. It's a Flashforge Adventurer 3 Lite, and while the quality is really quite good for a $299 printer, the nozzles come as a proprietary piece sold only by that company. I like the printer a lot, but in retrospect I would have bought something a bit more upgradable had I known.

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On 12/20/2020 at 2:14 PM, Markeno said:

The 99/4a I got recently has a Mitsumi membrane type keyboard.  The membranes fail, which mine is almost functional but not usable.  So I got another 99/4a with the Hi-tek Stackpole keyboard.  Like Ed said, today the primary source of a working keyboard is to find another 99 to get a working keyboard...  I don't know what kind of keyboard the beige 99/4a I had decades ago was as it is long gone now.

 

I was looking at trying to repair or rebuild the Mitsumi.  I was looking at the possibility to use microswitches like smd Alps ones above.  I think that keyboard is a better option for such a conversion with the microswitches like that.  It is built a fair bit like Commodore 64 Mitsumi keyboards with the plunger design.  The keycaps are different, having a Plus shape to the contact, similar to Commodore 64 keycaps, but a different size.  As long as the Hi-tek is working well I don't have to rebuild it though.

 

If you would be up to sending me the file, I could try printing the part on my printer.  I doubt it is higher resolution.  I had seen reference that people have done it, and that it does take a good bit of sanding etc to make them work.

 

I feel like the plunger is in a pretty good place to release the source files now. I decreased the width of the internal bar from 1.6 to 1.5 mm and I changed the lower cut-outs to have a tapered top which I think provides a little extra strength. In printing with some gray filament I picked up I had issues with these snapping right at the top of those bottom cutouts, so I decided to try and reinforce that a bit. I haven't had any of the ones I printed in white snap, though, so I think that other filament is just poor quality. 

 

I don't think I have the notches quite right. After inserting a polished one, these sit maybe 1 mm lower than the original and I believe it's because I've got the side notches a little too high.

 

I've attached a zip file with the FreeCAD source file, plus two STL files, one with filleted edges and one without. The walls are so thin that slicing may cause some artifacting with the filleted version, so I included the non-filleted one just in case.

 

It should be rotated to the correct angle for printing. If not, make sure the protuding nubs are on the top. All of the overhangs are angled from that direction so they should be printable. If it fails on overhangs it's probably rotated the wrong way for printing.

 

Any feedback you can give would be helpful. See the readme file in the zip for more details.

 

 

 

hi-tek_key_plunger_A_17.zip

Edited by Nelno
Replaced zip file, fixed typos.
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On 12/19/2020 at 11:24 PM, Ed in SoDak said:

Interesting exercise. These days you could design a new pcb layout that fit the new switch pin spacing and have it made by Oshpark.

 

Too bad it seems the only source for one of the "good" TI keyboards these days is another console that happens to have a working one.

 

Ages ago I made a homebuilt wood case for a standard TI keyboard, connected to the console by a ribbon wire extender. It was very handy having a compact keyboard separate from the console. It had room on the right for a planned accessory keypad using double pole switches to add Function+Key for the arrow keys, edit, erase and so forth. Even ordered the DPST momentary mini switches, but that's as far as I got on the project. That console got stored away for some reason I forget. Still think about it from time to time. Maybe someday I'll come across the keyboard and stash of switches and wake that project up again.

 

I was considering the entirely new PCB approach, too, but that would involve a fair bit more learning on my part. The PCB for these keyboards is pretty simple, though, so I don't expect designing a new one with the same functionality would be very difficult. However, since the modern switches are quite a bit shorter than these Hi-Tech High Profile switches, and because you want the switches to be held in place by more than just the soldered contacts, some sort of support structure to snap the switches into would still be required. In the end my guess is I wouldn't save anything by designing a new PCB. It might make such a project easier overall by removing some restrictions and limitations, but the extra freedom in key placement might also require a lot more prototyping to get things right.

 

Still, I am intrigued by the possibilities here. I just doubt I would have the time for such a project right now and I'm not sure it's really how I should spend my spare time, considering my work and some of the other projects I have in flight. But honestly, the things I could learn doing it do make it attractive...

Edited by Nelno
Fixed typo.

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Update: Printing these with PETG works much better:

- it is more flexible, which helps when inserting the plungers, which are designed to flex a bit to allow the nubs to go in.

- it seems to print more accurately and though it's more "stringy" it ultimately requires much less sanding an prep to get the pieces to fit.

 

I've attached a slightly updated file with the "nubs" fixed to match the original (affects depth after insert) and made minor adjustments to the wall width to accommodate (what I found to be) more accurate PETG printing.
 

hi-tek_key_plunger_B_3.zip

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