Clever girl... WAIT, these are not compatible?

[towmater]

I thought I'd save the trouble trying to fix my keyboard, and just swap in a TI-99 NOS keyboard.

The "A", "Q", "ENTER" and a few other keys don't work. This can't be right, right? They would not have changed the wiring scheme from the /4 to the /4A? should I waste time trying to find a fault or is this hopeless?

[Shift838]

24 minutes ago, towmater said:

I thought I'd save the trouble trying to fix my keyboard, and just swap in a TI-99 NOS keyboard.

The "A", "Q", "ENTER" and a few other keys don't work. This can't be right, right? They would not have changed the wiring scheme from the /4 to the /4A? should I waste time trying to find a fault or is this hopeless?

 

If the photo is the picture of your NOS keyboard, that still can be an issue.  It looks like a Mitsumi membrane keyboard, which are known to deteriorate over time, even if never used.  I have run into this before with these type of keyboards.  the ones that actually have real solder points are the ones you need to look for to use.  Or convert over to use a USB keyboard as I have.

[+arcadeshopper]

I thought I'd save the trouble trying to fix my keyboard, and just swap in a TI-99 NOS keyboard.
The "A", "Q", "ENTER" and a few other keys don't work. This can't be right, right? They would not have changed the wiring scheme from the /4 to the /4A? should I waste time trying to find a fault or is this hopeless?

The pinout is documented for the 4a it should take about a minute to confirm with a meter if the 4 is the same

Sent from my LM-G820 using Tapatalk

[Omega-TI]

If it's a Mitsumi, it's very possible it's in need of overhauling.  It's not the easiest keyboard to mess with either.  

If it's not the membrane, sometimes, because of age, a wire can break in the ribbon cable causing havoc as well.

 

Greg, (arcadeshopper) sells replacement ribbon cables if that is what it turns out to be, if it's the membrane keyboard someone here posted instructions on how to repair it.

 

[towmater]

18 minutes ago, arcadeshopper said:

The pinout is documented for the 4a it should take about a minute to confirm with a meter if the 4 is the same
 

Some keys work. I was hoping for an easy answer, as it took me about ten minutes to open the case, figure out what was catching (right-angle cartridge header), determine whether to unhook the PSU harness or unscrew the assy. (one can't easily reach the PSU connector release tab,) work out how to close the case with the new longer, stiffer (don't) keyboard cable, close the case, reopen the case to find out what was rattling (sliding port door snuck away), reopen the case to reposition the power jack, reopen the case to figure out why the power-switch would no longer slide to the on-position...

 

I know I will need to go back in there at some point, the question is do I do that after refurbing the black keyboard, or do I waste time trouble-shooting something when someone here like a Tursi will know the answer. And yes, writing all of this was still easier than opening and closing a 4A.

[towmater]

31 minutes ago, --- Ω --- said:

If it's a Mitsumi, it's very possible it's in need of overhauling.  It's not the easiest keyboard to mess with either.  

If it's not the membrane, sometimes, because of age, a wire can break in the ribbon cable causing havoc as well.

 

Greg, (arcadeshopper) sells replacement ribbon cables if that is what it turns out to be, if it's the membrane keyboard someone here posted instructions on how to repair it.

I recently installed a NOS keyboard on a 1200XL, which had keys that would finally respond with repeated hard presses, but in this case the unresponsive keys are completely... unresponsive.  I guess I am going back in, although I'm not looking forward to removing the 25 small screws on the back of the keyboard.

[towmater]

For posterity...TI-99/4 keyboard and mylar:

 

[Omega-TI]

5 minutes ago, towmater said:

For posterity...TI-99/4 keyboard and mylar:

 

It that something on top of the keyboard, or are the traces toast?

 

 

[+arcadeshopper]

Some keys work. I was hoping for an easy answer, as it took me about ten minutes to open the case, figure out what was catching (right-angle cartridge header), determine whether to unhook the PSU harness or unscrew the assy. (one can't easily reach the PSU connector release tab,) work out how to close the case with the new longer, stiffer (don't) keyboard cable, close the case, reopen the case to find out what was rattling (sliding port door snuck away), reopen the case to reposition the power jack, reopen the case to figure out why the power-switch would no longer slide to the on-position...
 
I know I will need to go back in there at some point, the question is do I do that after refurbing the black keyboard, or do I waste time trouble-shooting something when someone here like a Tursi will know the answer. And yes, writing all of this was still easier than opening and closing a 4A.

I ment the keyboard you removed should be easy to confirm the key switches are wired the same as a 4a keyboard

Sent from my LM-G820 using Tapatalk

[towmater]

37 minutes ago, --- Ω --- said:

 

It that something on top of the keyboard, or are the traces toast?

 

 

That's the point of failure for most mylar keyboards. My fix is to build a mound of solder onto the PC board, then use a piece of poycarbonate (shown here temporarily clamped to the board until I can melt screw holes into it) to put many times more pressure on the connections compared to the original.

[towmater]

And so, the answer is, yes, the two are fully compatible, electrically. The compression trick works.

 

[RickyDean]

9 hours ago, towmater said:

I thought I'd save the trouble trying to fix my keyboard, and just swap in a TI-99 NOS keyboard.

The "A", "Q", "ENTER" and a few other keys don't work. This can't be right, right? They would not have changed the wiring scheme from the /4 to the /4A? should I waste time trying to find a fault or is this hopeless?

Is this beige keyboard from a TI99/4? It looks just like a beige TI99/4a keyboard.

[towmater]

4 hours ago, RickyDean said:

Is this beige keyboard from a TI99/4? It looks just like a beige TI99/4a keyboard.

Probably they used the same tooling. Most beige 99/4a keyboards had computers attached, from what I understand, the inventory of 99/4 keyboards were purchased by a Texas-based computer retailer and resold as "experimenter's Special Purchase", thus the New Old Stock status.  I guess a key identifier would be whether the beige 99/4a's used the mylar method.

[JB]

The 99/4 used "calculator keys" instead of "real" keyboard buttons. It also had fewer modifiers(no function key, if I recall).

[RickyDean]

40 minutes ago, towmater said:

Probably they used the same tooling. Most beige 99/4a keyboards had computers attached, from what I understand, the inventory of 99/4 keyboards were purchased by a Texas-based computer retailer and resold as "experimenter's Special Purchase", thus the New Old Stock status.  I guess a key identifier would be whether the beige 99/4a's used the mylar method.

This was a beige 99/4a keyboard, not a 99/4 keyboard, though it could be used on one I believe.

[Tursi]

The 4 scan matrix isn't the same as the 4A scan matrix... it also has fewer keys (as has been noted). Even the joysticks are on different CRU pins...

 

Even if the physical remap accommodated the different CRU connections, the maps I have don't match between the two systems.

 

Also, the 99/4 keyboards were soldered to the motherboard, they didn't have connectors.

 

http://www.mainbyte.com/ti99/computers/ti994.html

 

 

 

[towmater]

The word is spoken...

 

The NOS keys sold as Archer are labeled (on the back) as 99/4, but they are really 4A's. This might be good news, if you have a 4A with keyboard issues (or just missing keys) there is often one of these replacements on eBay.