Re: Apple //e joystick problem

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

Kellion asked:

>     I am having a strange problem with my Apple //e's joystick.  Any game
>that I go into always presses me down.  I can move left, right but not up.
>I have tried multiple joysticks and confirmed that those joysticks do in
>fact work on other Apple //e's.  Anyone have a clue?

Assuming that the joustick(s) are properly "centered", it sounds like
a problem in the Y-axis timing circuit.

Try a simple BASIC program to display the "paddle" values as
you move the joystick around:

100 ?PDL(0), PDL(1)
110 GOTO 100

You should see two "streams" of numbers running up the screen,
with the value of one controlled by the joystick's X position and
one controlled by the Y position.  They should vary from 0 (or
near 0) to 255 (or near 255), with values near 128 when the
joystick axes are centered.  (If the joystick has "centering"
adjustment pots, they should be adjusted so that with the
stick centered, the numbers are very close to 128.)

If this program produces different results on the non-working
machine compared to the working ones, then you have
confirmed that there is a problem in the non-working paddle
circuit--ranging from a bad connector to some more interesting
circuit problem.

-michael

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