Fw: Asteroids SOLUTION!

 Hello Guys,

 I have found the culprit!!!

 Thanks to Jed Margolin's very comprehensive 'Secret Life of Vector
Generators' document, which is VERY GOOD if you really want to understand a
bit about how our favorite games work, I found that the output of LS04 at L5
was only swinging from 2.5 to 5 volts, it never went any lower. this
affected the Stae Machine's VMEM handling, that is why the self-test was all
okay but the game went bonkers.

 Im just so HAPPY!!!

 Cheers,

 Mendel

> ----- Original Message -----
> From: <mypearl@dds.nl>
> To: <vectorlist@vectorlist.org>
> Sent: Wednesday, June 25, 2003 3:40 PM
> Subject: VECTOR: Asteroids - getting there...
>
>
> > Hello guys,
> >
> > I have een working for many many hours on my Asteroids board since I
last
> asked
> > you guys. I have made some good progress. First, the board was dead,
> watchdog
> > resets happening. After replacing one 2114 RAM and all LS157 data
switches
> (all
> > were or went bad) The board played well, even video output, altough it
was
> > distorted (jagged X output).
> >
> > After replacing one LS374 latch, LS157 selector and analog parts in the
X
> > counter section, the output is clean... but now the board is caught in a
> loop
> > and draws the same random vector over and over as can be seen in the
> following
> > link:
> >
> > http://www.mypearl.dds.nl/Asteroids/Asteroids_large.mpg (1.3MB)
> >
> > or
> >
> > http://www.mypearl.dds.nl/Asteroids/Asteroids_small.mpg (135 KB)
> >
> > As you might be able to see from the screenshot, a lot of sensible
things
> are
> > displayed: Atari copyright notice, Insert coins, the saucer, your
> spaceship,
> > the test screen and some moving asteroids (all togheter!).
> > Depending on the coin DIP switch settings and language the displayed
> images are
> > different!
> >
> > The weird thing is, in TEST mode EVERYTHING is okay! No RAM/ROM errors,
no
> > distorted vectors... Just as if there is no problem with the board.
> >
> > I have checked all logic signals (even all unnamed TTL inputs and
outputs)
> in
> > the Vector Generator logic (sheet 2A). All signals are alive, except
> > for '/DMACNT', which is decoded directly from the MPU address bus by L6.
> It is
> > always high. Replacing L6 does not fix it. Could this explain why I am
> getting
> > this? What is the /DMACNT used for?
> >
> > I really hope you guys can set me back on the right track... would be
> eternally
> > grateful! :)
> >
> > Cheers,
> >
> > Mendel
> >
> >
>
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> > ** questions, comments, or problems to chris@westnet.com .
>

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Received on Wed Jul 2 16:30:19 2003