Apple II Computer Info
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### FILE : ii+keyboards
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### Created : Saturday, July 12, 1997 Modified: Saturday, July 12, 1997
### File Type: "TEXT" File Creator: "LMAN"
### File Size: 3049 bytes 2 KB
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Newsgroups: comp.sys.apple2
Subject: Re: ][ + control key locked
Date: Sat, 12 Jul 1997 07:26:10 +0000
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>
> Anyone have any experience with keyboard encoder chips and such?
>
> I have a ][+ with a keyboard symptomatic of control key always pressed when
> it isn't. ie. press the single key 'g' get beep....press 'm' get cr etc.
> Keyboard appears to be functioning properly by process of elimination but I
> don't have another encoder chip to try.
> Has anyone purchased parts for a ][+ recently? Would like as near original as
> possible.
Are you sure that your CTRL key is not stuck? (Try diddling the key.)
Another possible source of the problem is a KB Controller IC pin making
poor contact with the line coming from the CTRL key circuit. (Try removing and
re-socketing the KB IC.)
U1, a 7400 quad nand gate IC, could have gone bad or be making poor
contact at some pins. This could result in an 'always-pressed CTRL key' signal
at pin 11.
When the CTRL key is not pressed, pins 12 and 13 of U1 (connected to the
CTRL key switch) should be at nearly 5V and pin 11 (which goes to pin 19 of the
KB Controller IC) should be at logic "0" (roughly 0V - 0.25V).
If U1 pins 12 and 13 are at 0V (or very close) when the CTRL key is not
pressed, your CTRL key switch is, probably, stuck.
If U1 pins 12 and 13 are at/near 5V and pin 11 is not near 0V, U1 is
probably bad or making poor contact at some pins.
Apple II Computer Technical Information : Apple II Family Hardware Info
ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 198 of 572
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