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ironnerd

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I bought a Beige TI-99/4A from E-bay for <$30 (incl shipping).

 

I built the Composite cable adapter, and it didn't work. I figured the machine was just dead. Then I looked at another diagram and realized I was looking at the wrong end of the DIN plug and had the pins transposed. A quick bit of de/re-soldering and I had a picture (woo hoo!). Even better it is a 1981 OS (y'know... in case I find an Atari cartridge at Goodwill).

 

Now most of the keys don't work. The connection is (like everything in this machine) very clean. I kept hitting the "1" key until it started to work. The same "method" worked on a few other keys. Seems like this is caused by funk on the key contacts. Anybody know a less-complicated fix?

 

(pictures to follow - once I upload them from my phone).

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I bought a Beige TI-99/4A from E-bay for <$30 (incl shipping).

 

I built the Composite cable adapter, and it didn't work. I figured the machine was just dead. Then I looked at another diagram and realized I was looking at the wrong end of the DIN plug and had the pins transposed. A quick bit of de/re-soldering and I had a picture (woo hoo!). Even better it is a 1981 OS (y'know... in case I find an Atari cartridge at Goodwill).

 

Now most of the keys don't work. The connection is (like everything in this machine) very clean. I kept hitting the "1" key until it started to work. The same "method" worked on a few other keys. Seems like this is caused by funk on the key contacts. Anybody know a less-complicated fix?

 

(pictures to follow - once I upload them from my phone).

 

depending on which keyboard you have.. if it's a mitsumi you are probably going to have to take it apart and do the "fix" the instructions on this are in the FAQ https://atariage.com/forums/topic/267055-new-to-the-group-ti-994a-faq-hardware-and-software-resources-read-first/?p=3791726

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If any hardware builders are looking for a new projects, we need someone to take on a replacement keyboard like the Amiga guys are getting these days. A drop in keyboard circuit board to replace all the Mitsumi would be super.

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If any hardware builders are looking for a new projects, we need someone to take on a replacement keyboard like the Amiga guys are getting these days. A drop in keyboard circuit board to replace all the Mitsumi would be super.

 

Just do the USB modification. Works great. I have two TI consoles with the F18A and USB, and I use them via a 4 port KVM (VGA/USB) to my wireless keyboard. Which does not effect joystick operation when I have Caps Lock on, while the TI is selected. Nice :)

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Pics!!!!

 

Start-up

post-66893-0-53070400-1547160318.jpg

 

After pressing any key

post-66893-0-90348600-1547160327.jpg

 

After pressing "1" for TI BASIC. Note, after tapping every key repeatedly, I found very few of them actually worked.

post-66893-0-81934400-1547160335.jpg

 

There is some forced perspective going on in these pics. The TV is actually a lot larger than it looks... it's just a few feet farther away than the 99.

Edited by ironnerd

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If any hardware builders are looking for a new projects, we need someone to take on a replacement keyboard like the Amiga guys are getting these days. A drop in keyboard circuit board to replace all the Mitsumi would be super.

 

 

 

Just do the USB modification. Works great. I have two TI consoles with the F18A and USB, and I use them via a 4 port KVM (VGA/USB) to my wireless keyboard. Which does not effect joystick operation when I have Caps Lock on, while the TI is selected. Nice :)

 

How does that meet the requirements of a drop-in keyboard replacement?

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How does that meet the requirements of a drop-in keyboard replacement?

 

One way: JediMatt USB adaptor allows you to "drop in" a USB keyboard. I'm looking at portable USB keyboards that fit into the vacated rectangle.

 

On the other hand, a from-scratch keyboard PCB wouldn't need the USB adaptor. Any key layout could be translated to the 4A's matrix, using an Arduino Nano (maybe even an ATTiny) plus some lv165a, hct595.

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If your keyboard is a stackpole switch grid type, you might use Deoxit D5 contact cleaner to clean the contacts (just make sure the keyboard is completely dry before applying power to it. Also, you could take the corner of a dollar bill and put it between the contacts, press down the switch closing the contacts onto the dollar bill and gently pull the dollar bill out. A dollar bill is abrasive enough to clean but not too abrasive to damage the contacts.

 

post-65819-0-61050100-1547173315_thumb.jpg

 

post-65819-0-82772900-1547173323_thumb.jpg

 

post-65819-0-64947700-1547173332.jpg

 

 

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From the side, that looks suspiciously like a Mitsumi keyboard. If it is you really only have two options--perform the delicate repair procedure Arcadeshopper pointed to or replace the keyboard. The good news is that the rest of your machine looks to be operating fine, so that once the keyboard is in order, you'll have a really nice, working console.

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Check for cold solder joints too. In these keyboards the mechanical vibration of pushing a key translates directly to the PCB.

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If you can find a food spare, that will probably be less painful than repairing the Mitsumi, but the process Arcadeshopper pointed to will often fix one, if you don't damage the wrong parts of the keyboard while repairing it. The membrane is a bit fragile. . .

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Yesterday I purchased a white plastic TI-99/4A at a digitalpress store here in NJ. The keyboard did not work, same as the OP here...

I returned it after reading this thread. I don't have the time to repair it. Plus I have two working metal units.

Do most of the plastic white units have this keyboard problem?

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There were at least three different keyboards used with the beige units. Only one of them has the problems. The problem keyboards are relatively easy to identify too, as they have really sharp, squarish key tops. The other variants have a more rounded look to them due to the corners of the keys being a bit more curved. Once you see them side by side, you will never mistake one for the other again.

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There were at least three different keyboards used with the beige units. Only one of them has the problems. The problem keyboards are relatively easy to identify too, as they have really sharp, squarish key tops. The other variants have a more rounded look to them due to the corners of the keys being a bit more curved. Once you see them side by side, you will never mistake one for the other again.

Also if you look in the bottom vents the solder points are obvious on the good keyboards and the all brown is also on the mitsumi

 

Sent from my LG-H872 using Tapatalk

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Yesterday I purchased a white plastic TI-99/4A at a digitalpress store here in NJ. The keyboard did not work, same as the OP here...

I returned it after reading this thread. I don't have the time to repair it. Plus I have two working metal units.

Do most of the plastic white units have this keyboard problem?

 

odds are they have mitsumi's especially if they are the 1983 models..but you should ALWAYS check the vents and see if you see the solder joints or the brown mitsumi board.. both are documented in the FAQ which is pinned at the top of this forum..

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NOT SO DEAD!

 

I've been away a bit because I had no progress to report.

 

So my TI-99/4A is working. The Mitsumi keyboard is working quite nicely. Here is what I found:

I figured it had a bad trace, so I pulled the keyboard and disassembled it. The entire Mylar was stuck to the circuit board. So basically, nearly all the keys were being pressed at once. I slid a piece of card-stock between the Mylar and the circuit board. I put it back together and half the keys worked. In fact all the keys on the left worked.

 

So I took it apart again and shone a light on the Mylar form the back. I found two contact pads on the Mylar had a gap (where the Mylar makes electrical contact with the circuit board). I touched them up with some silver paste (not my favorite part of the job - got a little messy and I had to do some re-cleaning). I also noticed that most of key contacts were black with surface oxidation. I cleaned them up with a soft pencil eraser.

 

Now everything works! Booyah! It was actually a really easy fix, and it's not a terrible keyboard (I would rather have the mechanical switches, but I'll take it).

 

So... Now what do I do?

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That is some excellent intel on the inner workings of a Mitsumi, and the alternate ways to make it come back to life! When they work, they are a fantastic keyboard. BITD, a lot of people switched out anything else they had and replaced it with a Mitsumi. They just didn't age as well as the others, so now the pendulum is moving the other way. Known good repair methods may give them plenty of new life though.  Thanks!

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