Re: what is the voltage tolerance for a iie?

jonnosan wrote:
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.


How long is a cycle? I've watched the screen closely for a few
minutes, and also let it run by itself for a few hours and checked in
occasionaly, and not seen the "system OK" message.

I just timed it and, when repeating, the cycle is about 33 seconds.
However, when it it repeating (Open-Apple down) the "System OK"
message is not displayed, so what you are seeing is correct.

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".



I tried this, and there seems to be a good connection between ground
on the main board and ground on the keyboard. Also the LED on the
keyboard lights up when power is applied - would that happen if the
ground wire in the connector was broken? a visual inspection didn't
show any obvious damage to either end of the IDC connector.

While checking the ground connections, I did notice that on the
keyboard, all the pins on the connector seem to be connected to each
other (i.e. if i put the ohmmeter on any 2 pins, I get a low
resistance reading). Is that normal?

No, it sure isn't.

This raises a possiblity that I considered quite remote--that the two
modifier keyswitches (Open-Apple and Closed-Apple) are shorted (in a
state of being perpetually closed)--and it would appear that most of
the other keys are also shorted (but not both Control and Reset)!

The //e keyboard is simply a keyswitch matrix, in which each key
connects a "row" wire with a "column" wire when pressed (except for
the modifier keys, including shift keys, caps lock, control, reset,
and the two "Apple" keys, which switch their own dedicated wires.

I'm beginning to suspect that something bad happened to your keyboard
that caused corrosion--or something--that shorted many of the
keyswitches. If this is the case, replacing the keyboard is the
only thing that really makes sense.

A quick way to bypass the keyboard faults and check that most of the
rest of the machine is working would be to *unplug* the presumeably
faulty keyboard and connect PB0 to ground. This is pin 7 of the
keyboard connector, or pin 2 of the 16-pin game port DIP socket near
the back of the machine. Alternatively, if you have a joystick,
connect it and one of the buttons will be PB0. Pressing the button
will be equivalent to *not pressing* the Open-Apple key, and should
cause the self-test to complete after one cycle, displaying the
"System OK" message in the middle of the screen.

If this works, as I expect it to, you will need to get a replacement
//e keyboard to fix your system.

It would also be a good idea to disassemble the faulty keyboard to
see the inside of the keyswitches--there must be something interesting
going on in there! (BTW, the keyboard *has* been completely dry for at
least a couple of weeks, hasn't it?--just a thought.)

Thanks for your advice

You're quite welcome--let's see if we can get this working!

-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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