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restoring the keyboard


dphirschler

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Any tips for restoring the keyboard. Of the two keyboards I've tried here, niether works. I imagine some contacts need to be cleaned. Has anybody else done this yet? I'd like to know how best to clean the contacts (that is if that is what needs to be done). Is it as easy as contact cleaning spray, or should I use isoprophil, or pencil eraser, business card, sandpaper? Maybe it's not contacts but something else... I don't even know hot to take the keyboard apart. I only know how to remove the entire keyboard unit.

 

... tips anyone?

 

 

 

 

Darryl

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There are a few keyboard models.. two i have here, one with square key holders with spring switch contacts inside, and one (mitsumi) with mylar and traces.. the spring is the better of the two as you can actually fix it if it fails.. I have an entire crate of the mitsumi keyboards that i got free and none of them work right.sigh

 

cleaning the spring ones is pretty much either spray with contact/brake/carborator cleaner and let dry or wash in the dish washer without soap and let dry.. I've had old 99/4a keyboards start working after some serious firm typing as well..

 

Greg

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On the "good" keyboards, all you need do is pop off the individual keycaps. Start on one side and gently pry up with a small screwdriver under the bottom edge of a key, it'll pop right off. Inside, you'll see a pair of copper fingers that connect when the key is depressed. Your favorite choice of contact cleaner, or alcohol and a q-tip. Watch you don't leave stray cotton q-tip fibers behind, or use one of the foam types. Watch you don't deform the contacts so they no longer touch when they're supposed to. Those foam q-tips are maybe too thick, so be careful.

 

Worst case, but also less risky with bending the contacts, take a thin piece of fine sandpaper, fold it so there's abrasive on the outsides of the fold and lightly burnish the inner faces of the copper fingers.

 

That's it, you've cleaned one key! Have a beer and celebrate, then in just 39 more beers, you'll be finished! In more ways than one, I suspect. ;)

-Ed

Edited by Ed in SoDak
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I have a Mitsumi keyboard. Not sure how to clean it, but I am attempting to take it apart to examine it. But I cannot even get to the circuit board to make the Alpha-lock mod, much less clean the keys. The Alpha-lock key is the one key that is holding everything together. All the screws have been removed, but it won't come apart. And I cannot figure out how to get the #@$^%$ alpha-lock key off.

 

 

Darryl

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I repaired my TI with a Mitsumi keyboard by repeatedly drawing with a pencil over the area with broken contact on the carbon part of the membrane. The whole thing peels apart to

reveal the membrane circuit. What reminded me to try that was how I unlocked an old AMD Duron processor years ago for overclocking purposes.

I don't remember anything to do with the Alpha lock key though.

Edited by Imperious
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  • 3 weeks later...

Thanks to a well-time trade with Darryl, I now have a non-v2.2 QI console. However, it came with a crapped-out Mitsumi keyboard. As well, two of the several spare beige keyboards I had were both Mitsumis: one which is crapped-out as well, and the other which I, unfortunately, sent to Darryl for a spare (I hope it works.)

 

I am not in any way inclined to try to fix these unless someone has a tried-and-true method or is willing to take both of them off my hands for repair.

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This may sound stupid, but have you tried replacing the black keys (on a good keyboard) with beige keys?

 

Darryl

 

That is a good idea, but not as easy as it sounds, especially in this day and age where keyboards are not so easy to obtain.

The majority of the black keyboards have a square peg that fit's in the square switch hole. The majority of the Mitsumi keyboards have a little cross like indent that goes over a post. I'm thinking it might be nearly impossible to find the right beast.

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This may sound stupid, but have you tried replacing the black keys (on a good keyboard) with beige keys?

 

Darryl

 

The thought crossed my mine, but...

 

 

That is a good idea, but not as easy as it sounds, especially in this day and age where keyboards are not so easy to obtain.

The majority of the black keyboards have a square peg that fit's in the square switch hole. The majority of the Mitsumi keyboards have a little cross like indent that goes over a post. I'm thinking it might be nearly impossible to find the right beast.

 

 

...this. Even the one I have in now, while I do not think it is a Mitsumi, has pegs and not squares.

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This may sound completely crazy, but...

 

I've seen other circuit boards designed and built on this forum. Maybe it's time for a Mitsumi citcuit board replacement project. Possible?

 

Other than that, the only option I know of it wait for a beige console to go up on Ebay and look for the ones with an "under" shot. You can usually tell if it has that brown color or a green circuit board.

 

 

Darryl

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This wouldn't be horribly hard to do using current keyswitches, so long as it was possible to arrange them in such a way that they fit into the TI case. I'll look at it, but there are no guarantees at this time. Of course, a keyboard on an extender cable would work perfectly in a wooden project box--I have one of those now that used the original TI keyboard. It wouldn't be hard at all to build something like that and put a cover plate in the console with an appropriate connector for the cable. . .

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This may sound completely crazy, but...

 

I've seen other circuit boards designed and built on this forum. Maybe it's time for a Mitsumi citcuit board replacement project. Possible?

 

Other than that, the only option I know of it wait for a beige console to go up on Ebay and look for the ones with an "under" shot. You can usually tell if it has that brown color or a green circuit board.

 

 

Darryl

 

I'd rather see the ps/2 keyboard adapter..

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I'd rather see the ps/2 keyboard adapter..

 

I would rather see a USB keyboard adapter. But that aside, given the choice, I am more interested in a stock-looking TI, so new TI keyboard is fine by me.

 

I like TI's "QI" moniker for "quality-improved". Commodore had a similar, as did others, called "CR" for "cost-reducted." IMNSHO, while "QI" may be technically accurate, Commodore was a bit more honest with its "CR" designation.

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There are a few keyboard models.. two i have here, one with square key holders with spring switch contacts inside, and one (mitsumi) with mylar and traces.. the spring is the better of the two as you can actually fix it if it fails.. I have an entire crate of the mitsumi keyboards that i got free and none of them work right.sigh

 

cleaning the spring ones is pretty much either spray with contact/brake/carborator cleaner and let dry or wash in the dish washer without soap and let dry.. I've had old 99/4a keyboards start working after some serious firm typing as well..

 

Greg

good advice. my g key was bad. i did the whole keyboard. good as new!

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  • 9 years later...

Your topic is now 10 years old, but I believe I could help if you still have issues.

 

I bought a TI-99/4A with a Mitsumi keyboard that was completely dead.  I was able to make it "good as new" with isopropyl alcohol and a conductive ink pen.

 

That's almost all you need to know, but if anyone wants to know more, just reply here and I will post details.

Edited by PasadenaBrad
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8 hours ago, PasadenaBrad said:

Your topic is now 10 years old, but I believe I could help if you still have issues.

 

I bought a TI-99/4A with a Mitsumi keyboard that was completely dead.  I was able to make it "good as new" with isopropyl alcohol and a conductive ink pen.

 

That's almost all you need to know, but if anyone wants to know more, just reply here and I will post details.

I am going to ask, not because I have a problem, though I might in a couple of my TI99 systems, but for posterity sake for all here on Atariage. It will probably be good info that will not go to waste. Thanks.

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On 3/27/2024 at 7:35 AM, RickyDean said:

I am going to ask, not because I have a problem, though I might in a couple of my TI99 systems, but for posterity sake for all here on Atariage. It will probably be good info that will not go to waste. Thanks.

Okay, I'll report my process.

 

I would say that, before going down my path, view this video at Max's Garage on Youtube.  He was able to get his keyboard working just by going over it with a heat gun.  I don't fully understand why that would work, but it apparently worked for him.  I didn't find his video until after I had pulled my membrane off, which was too late.

 

So here are my steps.

1. The first thing you have to do is desolder these two wires which are connected to the Alpha Lock key.  Super easy.  Max's video shows him doing it.  You don't need to pull the wires off or anything.  All you're doing is freeing the two pins that are protruding through, so that you can lift the circuit board off of them.

image.thumb.png.8337c8dfe34bd9452f359d59a1dc3412.png

2. Once desoldered, remove the ~15 small screws (there's one hiding under the ribbon cable) and lift the brown panel with the keyboard membrane off the keys.  Flip it over and you'll have this:

 

image.thumb.png.4c25f368ffc8d486eeb7208f924f6741.png

What you've got is an ordinary circuit board beneath, with copper pads.  The white thing is a thin membrane.   On the underside of the membrane are traces and pads made of conductive carbon; you are seeing them from the back side.  (The function of the membrane is to provide a very thin gap between the copper pads below and the carbon pads above.)

 

3. Next, get the key matrix map (I got it from here, pasted in below). 

 

Stick a pair of wires into the connector at the end of the ribbon cable and move them to different pins and try out various keys (just press the pad on the membrane into the circuit board) to see if the circuit closes.  Even when perfect, none of the contacts will read 0 ohms.  (All of mine were infinite when I first tried them.)

 

10-30 ohms is good, anything under 75 ohms is arguably good enough.  I did a deep dive on the schematics and TMS9901 datasheet and did the math and found that anything below 244 ohms should register, with all specs at worst case.  In practice, you'll want to refurbish all the keys, so you might not bother with the resistance measurements now, but it's worth doing it later before you button it up again.  (It's a pain to remove and re-install all tine tiny screws.)

image.thumb.png.cd4d39b1ff743c0ed2807bb761a75e6b.png

 

4. Now is the sensitive part.  You might be able to do better than me.  What you're going to do (but read a little further first!) is pull the membrane off and set it aside.  I recommend setting it down carbon-side up.  It's slightly tacky and you don't want any dust on your lab bench to stick to it.

 

But do it with care.  What I found is that in this region, the membrane and circuit board had fused together:

image.thumb.png.2a1fa47c349a31cd3aadefb97c3c9a59.png

When I pulled the membrane off, large portions of the carbon fingers stayed behind.  As far as I can tell, it was a carbon-on-carbon contact. 

What Max does in his video is uses a heat gun and is able to get it to come apart more readily, apparently.

 

At that point, in my case, it was necessary to repair the traces.  Back to that in a moment.

 

 

5. From here, I don't have a photo, but what you want to do is clean the carbon contacts on the membrane with 90% isopropyl alcohol and a cotton swab (I recommend a wooden-handled one over an ordinary Q-tip, just so you can generate a bit more force.)

As you clean each contact, your Q-tip will turn black.  I assume that you're pulling up oxide and debris - I imagine that going hog-wild could wear through the contact.  I just rubbed each one with modest force for 2-4 seconds.

 

I also cleaned the copper on the circuit board, but I didn't notice it having any obvious effect.  And later, when I had to deal with a few recalcitrant keys, it was cleaning the carbon side more thoroughly that got them all going again.

 

 

6. Okay, time to repair those fingers.  I got myself a CircuitWorks CW2900 conductive ink pen (flex type, since there is a little bit of flexing anytime you lift the membrane off, and the flex stuff was cheaper anyway).  I traced the damaged contacts on both the circuit board and membrane side.  You can be a bit generous with it.  The good news is it's not a super-precise operation - the fingers are pretty well spaced apart.  Let dry for 45 minutes. 

 

 

7. Once cleaned and dried, lay the membrane back onto the circuit board.  Get out your key matrix map and try out your keys one by one.  (You don't need to try Alpha Lock, since it's not a membrane key.)  This will seem daunting at first, but really it only takes about 10 minutes.  And considering the pain of putting those 15 tiny screws back in and taking them out again, it's definitely the shorter path.  I ended up doing three full disassembly/assembly cycles before I had mine fully working.  Don't be like me.

 

You might be tempted to let 50- or 60-ohm connections slide at this point, but as long as you have it open, I'd go ahead and try to get them all to 30 ohms or below.  You'll get a feel as you go through them all where the "floor" is that you're shooting for.  After all, who knows how it's going to age.  The lower starting point should give you more margin.

 

 

8. Now reassemble.  You'll need to resolder the two Alpha Lock wires you desoldered earlier.

BUT!!!  As long as you are at this point, this is the perfect time to go ahead and solder in a diode for the Alpha Lock/Joystick fix, because it's trivial with the Mitsumi keyboard.  (BTW, this isn't just a hack.  It really is fixing a design flaw.) 

 

However, I will amend the online instructions just a little.  They suggest a 1N4148 diode, but after a deep dive into the datasheets and schematics, I concluded that the 0.6V drop of an ordinary diode puts you on the hairy edge.  Use a Schottky diode instead.  Any one will do.  I used a 1N6263, and it ended up looking like this.  (I elected not to trim the existing lead in case I wanted to back out the fix, so just kind of folded it up instead.)

 

image.png

 

 

9. As you reassemble, be sure to fully tighten all the screws, especially around the contact fingers.  It's important that those be in good contact.

 

 

 

The end.  I'm interested to hear of anyone else's experience if you try this, particularly longevity of the fix.  Mine is only a couple of days old at this point, so I can say for certain that it's not going to go bad again in a few days, but I can't see why it would.  My guess is that regular use could help prevent build-up of oxides or contaminants and would make it last longer.  But that's just speculation.

 

 

Good luck,

Brad

 

Edited by PasadenaBrad
Corrected final image with the correct diode orientation
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Nice writeup, Brad!

 

I recently had a go at this as well, and did not have the success you did.  I did not do everything that you did, so I will go back and try it when I get some time.

 

When I received my keyboard, only one key worked.  Now, most of the keys work but there are few that do not.  Of the ones that do work, there are many that need debouncing.  That is, when I press a key once, I get 4 - 5 characters on screen.

 

My research found a lot of the same fixes as described in your post, but I did find one other possible fix.

 

1. Max's video, which heats the mylar with a heatgun.  I tried this but it had no effect for me.

2. Cleaning the carbon pads with alcohol.  I did this and it certainly improved things for me.

3. Fixing the traces on the keyboard and mylar.  I did not do this, but will go back and do so.

4. Making the keys stiffer, using some heat shrink.  I tried this but don't have the right sized heat shrink, and gave up on it.  Here's the video:

 

 

I think that over time, a lot of things can degrade on this model keyboard.  Each keyboard may have its unique failure points; so a particular fix for one keyboard might not resolve issues with a different keyboard.

 

 

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