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Re: A plea: Looking for a working MM5740AAE/N for Apple II Keyboard



On Wed, 7 Dec 2011, rittwage wrote:

On Dec 7, 2:49 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
rittwage wrote:
I have an old Apple II that I've fixed every other odd problem
(besides a broken Applesoft E0 ROM) except the keyboard!

I found some AAC/N chips, but no luck- the encoding is wrong.  I need
to see if any kind soul has any AAE/N encoder chips left to spare.

I really hate to convert to PS/2- I like the original keyboard.
Without that, I might as well use an emulator.  :)

Pete, I'd recommend keeping this thread in csa2 and avoiding
crossposting to marketplace and emulators.

Are you sure that the problem is the encoder chip, and not
one or more shorted keyswitches?  Failed encoders are not
the most common keyboard problems.

If it is the encoder, then you will have a hard time finding
an equivalent replacement.  It would be possible to construct
an equivalent that plugs into the original electrical "footprint",
but it's not a simple project.

Since the encoder presents parallel ASCII to the Apple II, it
should not be too difficult to replace the keyboard with, say,
a later Apple ][+ keyboard.  Those used to be pretty plentiful,
depending on how authentically "Apple" it had to be...

-michael

It's definitely the encoder- the original does nothing and the AAC
works, but has all wrong keys.  No switches are shorted, and I traced
to find no "stuck" bits.  It's just that the AAC, AAD, etc. send
different keystrokes to the AAE.

This is an early Datanetics keyboard without the separate encoder
board, so that modern encoder board replacement won't work.  Also, I
know I can replace the keyboard entirely with a PIC and a PS/2
keyboard, but... yuck.  I know I can also swap the whole keyboard for
another, but they are about as hard to find!

I do have extra IIe keyboards, but to my knowledge they can't be
converted.  Or can they?

Map what character is generated with what key.

Then program an eprom as a translater, taking the 7bits from the encoder
and outputting the proper 7bits that actually goes with key. In other words, the character that comes out of the character generator is used as an address for the address pins of the eprom, and the data at that address will be the proper ascii character.

  Michael