Apple II Foil tab keyboard (again)

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Last seen: 4 months 4 days ago
Joined: Nov 24 2013 - 13:23
Apple II Foil tab keyboard (again)

Hey guys,

So summer is over and I'm back to my other expensive hobby. I'm trying desperately to revive this II+ foil tab keyboard I have, but seem to be getting nowhere. I think what I am lacking is an understanding in the principle of the thing, how it's supposed to work, how different characters are generated, etc.

For example, my 1 and 2 keys don't work at all. Superficially, comparing them to the nearby working 6 key, they seem fine -- seem to have the right amount of travel and the two little 'fork tines' beside 1 make contact with the PCB. Further, the PCB I know works because I've tested it without the keys in place.

Sometimes 1 works and it'll generate a minus sign. Sometimes you hit 4 and it generates 4545 or something like that.

Are there any good guides out there for these particular keyboards? I'm thinking it may be at the point now where I need to just write it off because there's just too much wrong with the tabs.

speedyG's picture
Last seen: 23 hours 58 min ago
Joined: Nov 16 2011 - 07:45
Re: Apple II Foil tab keyboard (again)

Hello falter,

there are several areas that can cause issues with the keyboard....

some at the keyboard itself ( encoding and sending ), some with the cable ( transmission to mainboard )
and last but not least some at the mainboard itself ( passing code to Chargen ROM and from there to
Databus )

allthough i have not made specific page on this topic some general pages might lead you adhead:
understanding the keys and keyboard encoding at the keyboard:

checking the cable for possible intermitant shortcuts or bad contact
you should perform measurements at the cable itself and
at both ends examine good fitting and good contact with the contactsockets
- also thinking about the possibility of "worn-out" contacts in the socket
that don´t create firm contact with the cableplugs or bent cableplug pins!

and at the mainboard examining the related section of the keyboard:

Finally sometimes,because the foil tab keyboard is not working in "switch-mode" but instead
in a kind of "change capacity mode" the passive components at the keyboard itself
(resistors and capacitors ) can cause trouble besides the integrated circuits -
so its recommended to also hunt for :
bad soldering joints or nearly broken wires from passive components to PCB....

besides: cory cohen has posted some excellent threads on restore and demounting and mounting
of that keyboard ( it´s really bad timeeating task with a bunch of pitfalls !)
spotting out his "toothpick-trick" and therefor it´s highly recommended to read that
and view the pictures he made ( about 2 or 3 years back )
before making attempt to dismount that keyboard....

happy search and rescue... and good luck....
sincerely speedyG

Last seen: 4 months 4 days ago
Joined: Nov 24 2013 - 13:23
Re: Apple II Foil tab keyboard (again)

Thanks speedy. That graphic you posted is awesome!

I am confident the PCB, the cable, associated motherboard chips and encoder are all fine. I have a spare keyboard and have tested most of the components with that, and the PCB I've tested just shorting contacts. I've successfully reassembled the keyboard a few times, but on the last attempt (replacing a broken stalk) it all went haywire. If i bend the tabs in just the right way sometimes i can get some of the dead keys to work briefly. What I am wondering is, you know how certain adjacent keys are linked (ie one continuous foil tab strip will reach across five keys).. vs some keys that are by themselves... is that significant? One of the keys I had trouble with was on a ling strip that got bent.. so I cut it and put down an unbent strip, trying to maintain contact.. wondering if thats part of my problem.

I will look for that thread. Thanks!!

macnoyd's picture
Last seen: 2 hours 15 min ago
Joined: Oct 15 2012 - 08:59
Re: Apple II Foil tab keyboard (again)

This is a unique illustration.
I have a "Singapore copy" motherboard that I've been mod'ing back to the Rev. D Apple II motherboard standard and this will be a HUGE time saver.
Thank you for taking the time to do this and sharing to the Forum Speedy! ++A++

speedyG's picture
Last seen: 23 hours 58 min ago
Joined: Nov 16 2011 - 07:45
Re: Apple II Foil tab keyboard (again)

Hello falter,
you might be fighting different kinds of issues....
the base material can loose flexibility and get very small so called "micro breaks"
in such case it might be needed to "mend" a trace with very small amount of pure silver liquid
( difficult to get and very expansive ! )

one well known issue are the so called "stiffeners" at the rear side ( bottom ) that are added to prevent the
keyboard from bending down while key is pressed....
Maybe it´s usefull to think about alternate possibilities of prevennting the keyboard from "bending" while in use
or while key is pressed....

Some of those keys use inside a kind of foam to carry the capacitative plate....
it´s known that that foam stuff gets bad ( looses its flexibility or even starts crumbling ) ....
in such case it might turn out needed to replace that stuff....
and in such case it´s realy important that the spacing between plate and foil is exactly same as before !

Related to the question of the matrix ( relation of the different keys to each other )
i just recommend you to visit that basic pages i mentioned about keys and basics on keyboards....
one complete page there is related to explain the way matrix is working and displaying the
used chips and the used matrix schemas......

just also recognized that you found that mentioned thread from Corey and added some questions there...

sincerely speedyG

Last seen: 4 months 4 days ago
Joined: Nov 24 2013 - 13:23
Re: Apple II Foil tab keyboard (again)

Thanks speedy. If I ready Corey's thread right.. I have a ton of shorts going on. Off pin 4 (without the encoder in, and minus the circuit for the light bulb), I found 7 shorts. I then followed the traces and elominated the first two by rebending the tabs a bit. But.. im starting to think this keyboard may be a lost cause. I'm going to keep trying. I wish I could just sub in another 2+ keyboard I have here but its an earlier pre-tab model and the mounting is different.. needs shorter screws. Oh well.. all fun in apple land. Wink

speedyG's picture
Last seen: 23 hours 58 min ago
Joined: Nov 16 2011 - 07:45
Re: Apple II Foil tab keyboard (again)

Hello falter,

if the timeeating task gets to wierd: I made the experience that in nearly all cases the
Apple II case accepted the change to other kind of Apple II keyboard!
Only in very few cases
it was needed to do a little "work-around" with some sandingpaper....

Problems with exchangable similar keyboards just rise if you try to replace
with a keyboard from a taiwan clone.
The taiwan clones often did not stay within the original
of the original case....

Another rather larger problem is that those keyboard were sold few years ago
at ebay at reasonable prices and within the last 2 years that prices rocketed straight through the rooftop...
i´ve seen keyboards being sold for more than 100 bucks ( a price you can get 1 or 2 complete IIe´s )!

In fact: IIe keyboards have other decoding and won´t fit....

At the other hand in the last years several members have been building Apple-1 replicas and
therefor are hunting for Apple II or II+ kind keyboards... but in conjunction to those, who want to
perform exchange within a original Apple II case that guys are not restricted....

... - as i mentioned in earlier in another earlier posting:
the apple-1 boards have other ( longer ) measurements and therefor
won´t fit anyhow in an original Apple II case -
so that guys have to make anyhow a "custom built" case
therefor they can also be satisfied using a Clone keyboard with varying measurements.....

The clone keyboards still have the same outlining at the 16pin flatribbon plug
which is the only requirement for use at the apple-1 replica.
And Clones are ( compared to original Apple II ) sold "dirt cheap" .

So if that guys would follow up my advice buying clone-keyboards
the original keyboards required for replacement in original Apple II´s would not have rocketed up that high....
and kept at reasonable prices for those who want to repair their Apple II and
who therefor are restricted to the original Apple II keyboards because of the measurements.....


Last seen: 4 months 4 days ago
Joined: Nov 24 2013 - 13:23
Re: Apple II Foil tab keyboard (again)

Yeah the original keyboard prices are insane. I would have thought the II/II+ keyboards would still be plentiful enough to keep prices down. I'd kind of like to maintain the correct keyboard for this unit if I can.. but I've only rarely seen the foil tab ones come up.

Speaking of clones.. I am looking for either a rrplacement ROM for a Unitron 2000 keyboard or a whole keyboard to replace the one in my Linden, if anyone sees o e

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