R: I: STAR CASTLE PCB with a "little" problem

I'm sorry for the quality of my video, but if you look it carefully you can
see the "rings" of the castle shake a little bit. But if you look more
carefully the rings don't shake , they are simply drawn with some segment
vertex wrong for a short time, just a "frame" (I know we don't have frames
in vector games). The same happens with the animy starship: when it rotates
in some positions and for a very short time, some vertex are wrong. So
definitely it is not a problem limited to one object.
I already changed 181 TTL RAMs and ROMs

thank you,
vernimark
  -----Messaggio originale-----
  Da: owner-vectorlist@vectorlist.org
[mailto:owner-vectorlist@vectorlist.org]Per conto di Chris Leyson
  Inviato: mercoledì 8 giugno 2011 10.04
  A: vectorlist@vectorlist.org
  Oggetto: Re: VECTOR: I: STAR CASTLE PCB with a "little" problem

  I would initially suspect a problem with the ROMs as the fault seems to be
specific to the starships. However, if any variables used in the starship
drawing routines are held in a specific place in RAM then there could be a
problem with the RAMs, try using RAM from another board. As William says,
the game would not work properly if one of the ALU logic chips had failed
and all the other vectors draw OK.

  Chris

  On 08/06/2011 04:00, William Boucher wrote:
    I thought that your video was very interesting and it certainly
demonstrated the problem. The rotation of a ship or ring is a math
intensive and relatively complex procedure that involves EPROM lookup tables
(for both the basic object drawing data and Sin/Cos data), the ram chips
(L14, M14, N14), the '181 ALU chips (L6, M6, N6), and many other ICs
(assorted gates, latches, data selectors, etc.). Since so much of the
general game operation also depends on many of the same chips that deal with
all of the rotation calculations, I would not expect the game to run
properly if one of them was failing. I would expect the game to crash.
Since you say that you tried several chips (EPROMS, ALUs, RAMs) in another
board and they worked then we'll consider them proven okay. This also
eliminates the 34-conductor ribbon cable and the monitor as a source of
trouble. The condition of the chip sockets on the problem board may remain
an issue but like I said already, I would expect a crash if this were the
case because such a fault would mess up a lot of things, not just rotation.
If I were to assume that the sockets are okay, and since the game play is
okay and the problem appears to only effect the picture, then I might
suspect the video data output latch chips (74LS377 at M2, P2, S2).

    When I watched the video, I got the impression that the misplaced vertex
was shifted mainly (or entirely) in the "Y" axis. I could be wrong about
this since I only watched it a couple of times however for this moment I'll
go with it. The 12-bit "Y" data is output as 3 nibbles (4 bits each) where
each nibble is latched by one of the 74LS377 chips M2, P2, S2 where M2 has
the least significant nibble and S2 has the most significant nibble. Since
the positional error is very small, I'd suspect a very low order magnitude
bit, so I'd replace M2 first. You might want to check the condition of the
J2 pins 1 through 13, the traces leading to the pins, and the solder on the
pins.

    William Boucher
    http://www.biltronix.com

    ----- Original Message ----- From: "vernimark" <vernimark@vernimark.com>
    To: <vectorlist@vectorlist.org>
    Sent: Tuesday, June 07, 2011 8:47 PM
    Subject: VECTOR: I: STAR CASTLE PCB with a "little" problem

      http://www.youtube.com/watch?v=n9h0c9qYkZM
      (sorry for the bad quality)

      In some starship positions vecrots are drawn with one wrong vertex.
The same
      happens with the castle and other starships. Any Idea?
      74181: ok
      ROMs: ok
      (on another PCB RAMs and ROMs work well)

      Thank you,
      vernimark

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