Re: Getting ap2222pc on the Apple II

[mjmahon@aol.com (Michael J. Mahon)]

MechCD wrote:

>----- Original Message ----- 
>From: "MechCD" <mechcd@bluebottle.com>
>Newsgroups: comp.sys.apple2
>Sent: Sunday, February 29, 2004 4:24 PM
>Subject: Re: Getting ap222pc on the Applle II
>
>
>> I'll try and check the connections again. I'm fairly certain the PC's port
>> works, I used to it print not long ago. How would I verify the contents of
>> the memory on the A2? Type in the addresses by themselves (0300 for
>> example)? I'll try my low quality o-scope on it if i can get it close enough
>> for the leads to reach.
>
>Ok, the connections were all correct. I unhooked the interface and attached
>my trusty joystick and fired up Choplifter. Now when i hit the main fire
>button, it restarts with grabled stuff all over the screen. If I hold it
>down, it restarts over and over, the power supply clicks, and the power LED
>(not light) flashes.
>
>Whats my chances of blowing something without trying? This was my functional
>Apple IIe... I have another, but a good portion of the keys don't work and
>i'm not sure how much of it works overall.

The buttons on a joystick are switches that connect the pulled-down
PBn input to +5v when they are pressed.

The fact that pressing one of your buttons causes a short of +5v to
ground (which explains the symptoms you describe) indicates that
the corresponding PB input is grounded.  This would, of course,
also explain why the PC cannot talk to the Apple II.

If you have a Platinum //e, this could be explained by a shorted
0.1uf bypass capacitor (near the external joystick port).  On any
//e it could be a short in the joystick connector or in the joystick
cable.

Or, worst case, ESD or severe overvoltage could have caused the
PB logic input itself to be shorted to ground.  This is an unusual
failure mode, but you have been connecting cables to the input...  ;-(

(It is interesting that this kind of short of +5v to ground can occur
on PB2 for any machine that has the shift key mod installed (as
the platinum //e's do by default), if the shift key and the button
corresponding to PB2 are both pressed at the same time.)

-michael

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