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Re: what is the voltage tolerance for a iie?



jonnosan wrote:
On May 12, 3:53 pm, Silicon Sam <Silicon...@gmail.com> wrote:

On May 11, 11:21 pm, jonno...@gmail.com wrote:> Howdy folks,


I recently bought an apple iie off ebay (it's my first apple ever - we
had BBC's at my school)

Unfortunately when I unpacked the apple and plugged it in, it seemed
to be DOA - the screen was always a periodically changing jumble of
blocks (photo athttp://www.flickr.com/photos/jonnosan/494345448/).
keypresses made no difference, nor did pressing reset (alone or in
combination with other keys)

 I seem to recall, it has been a long time ago, but it may have
something to do with the keyboard.  Make sure it's plugged in right,
and try it with it unplugged.  I think that block pattern is actually
a test mode Apple used when testing motherboards in a rack.  While
this block pattern is going on, does the speaker make any kind of
noise?  There is also an LED at the back of the motherboard that is
tied to the speaker circuit as well.  This was so Apple could set a
few hundred motherboards in a rack, power them up with power only, and
observe the LED.  When the LED was out, the test failed for that
board..


I've tried it with the keyboard plugged in, and with it not plugged
in, and it seems to make no difference. If I leave it turned on, after
about 30 seconds there are some blips that come out of the speaker,
and an LED (not the power LED, so might be the one you refer to)
flickers briefly, and the pattern on the screen changes (it's still
random blocks, just a slightly different arrangement).

There is nothing wrong with either main board.

That's the self-test running.  If it keeps running, it should also
display "System OK" in the middle of the screen for a few seconds
on each cycle.

There is a problem either with your keyboard if it is plugged in
correctly.

In particular, if the keyboard is plugged in and the Closed-Apple
key is depressed while the unit is powered on (or reset), the self-
test will execute.  If, in addition, the Open-Apple key is depressed,
the self-test will cycle endlessly.

If the keyboard is unplugged, or if the wires to PB1 and PB2 are not
"pulled down" to ground by 470-Ohm resistors on the keyboard, it will
"look" to the computer like both switches are depressed.

The simplest explanation for the behavior you are observing is that
the keyboard ground wire (pin 13 of the connector) is broken, either
at the IDC connector (from being pulled by the wire, for example) or
somewhere along its length.  (This would also explain why Reset doesn't
do anything.)

If you have an ohmmeter, check for continuity between a ground trace
on the main board and a ground trace on the keyboard, then shorten
the path until you isolate the "open".

-michael

NadaNet file server for Apple II computers!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
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