Re: Apple ][ Plus questions

[Rubywand <rubywand@swbell.net>]

Jason Whorton writes ...
> 
> Hello.  I have a few Apple ][ Plus questions that I hope someone can answer.
> I have two Apple ][ Plus's, and they are both giving me trouble.  I tested
> them one time, and I seem to remember one of the computers having a keyboard
> that worked fine and one that all the keys didn't work.  I had to take the
> power supply out of the good one (the bad one didn't have a power supply, I
> had just put one in temporarily to test it).  Now that I have gotten around
> to re-testing them, both keyboards don't work right with either motherboard.
> I was trying to swap parts around to make one computer out of two, but now
> it seems I have made zero out of two.  Both keyboards exhibit the following
> odd behavior:
> 
> some keys do not work
> 
> some keys display characters other than the one being pressed (for example,
> press "8" and it shows "0" (zero), press "G" and the bell rings like
> CONTROL-G, press "O" (the letter) and it dings, press "J" and the cursor
> moves up)
> 
> Could the CONTROL key be stuck with the key being in the normal "up"
> position?
>

     If some keys produce the correct character, the Control key is
probably not stuck. Besides, a stuck or shorted Control key would not
account for some of the mixups. For instance, an "O" would need to have
bit 3 forced to 0 in order to end up as a Control-G (BEEP); yet, the "J"
keeps its 1 at bit 3 and produces a Control-J line feed. And, for sure,
a Control-8 is not an "O".

     
  
> One motherboard says "Apple II Main Board".  It looks almost the same as the
> other motherboard, with a few small differences.  I am wondering if it is
> a ][ Plus board or a ][ board.  What are the differences?

     According to the Apple ][ Reference Manual (1979 white cover
edition), there were two major versions of the ][ motherboard: Revision
0 and Revision 1. One way to spot a Rev 0 board is that it did not
include a circuit to do a Reset upon power-up (however, this would be
easy for an owner to change).  Another Rev 0 feature is that it did not
shut off color when displaying an all-Text screen-- so, you would see
color fringing of an all-text display on a color monitor on a Rev 0 but
not a Rev 1.

     The manual says that the ][+ has a Rev 1 board. Since, Apple
continued to offer the plain ][ for a year or so after release of the
][+, it seems likely that some plain ]['s have a Rev 1 board. It is
possible that some Rev 0 boards may have had the "Autostart" and other
][+ ROMs swapped in.

     If both boards do an automatic Reset upon power-up and do not show
color fringing of all-Text displays on a color monitor, it is likely
that any differences are due to minor revisions to cut manufacturing
costs, permit using newer IC's in a few places, etc.. 


> Would it make a
> difference?

     There is no indication that different U.S. ][, ][+ versions use a
different keyboard plug. Some non-U.S. versions may-- do not know.


>  Could I have zapped a chip?

     Sure; but, it does not seem likely. If any single chip was or has
been zapped, about the only one which could produce such an odd mixup of
KB outputs is the large KB controller IC on the card mounted to the
keyboard.


     One thing to check is that the ribbon cable running from the KB to
the motherboard is in good shape. Use an Ohm meter to check that each
line (pin-1 to pin-1, etc.) shows a low resistance which does not go
high when the cable is flexed and that no line shorts to adjacent lines.

     A reasonably good suspect is the line which carries -12V (pin-15 to
pin-15). A KB controller which needs this voltage might partially work
even if the voltage is missing or reduced due to a break or near-break
in the KB cable.


     Since this whole business started with power supply problems, be
sure to check voltages. With all cards pulled, you can check voltages by
clipping one Volt meter lead to Ground and touching pins on a Slot:

Slot Pin   V

25         +5
50         +12
34         -5
33         -12

Looking down at a Slot from the front of the computer ...

_________ Back of motherboard _________


     26-o   o-25
     27-o   o-24
        .   .
        .   .
        .   .
     49-o   o-2
     50-o   o-1


     A good suspect is messed up output of -12V. The voltage is used
hardly anywhere else in the Apple ][; so, the computer might seem to be
working fine except for a screwed up keyboard.


     More? You can remove the keyboard and make sure the socketed IC's
are making good contact-- scootch up and re-socket each IC. If the big
KB Controller IC's pins are black with corrosion, re-socketing it to
establish fresh contact with socket pins could produce a 'magical' cure
of KB problems.

     Also, with the KB out where you can examine it closely, check for
evidence of Coke, coffee, etc. spills (loose wires, bits of metal, ...)
on both sides of the attached board and on the key matrix board. A few
Coke shorts on the matrix would produce odd key mixes such as those you
describe.



> How many licks to the center of a
> Tootsie Roll Pop?

     No one knows. Lickers always end up biting through to the Tootsie
Roll center when the candy shell is thin enough.



Rubywand