Re: Tempest troubleshooting

Joel Rosenzweig wrote:
>
> Hi guys,
>
> My Tempest just developed a problem that I've never come across before,
> so I was hoping that somone here might have some more insight into it.
>
> In attract mode, the "Game Over" text now appears 4 times larger than
> normal, and it shows up in the wrong location on screen. It flits
> between where it's supposed to be up top, and the middle of the screen.
> Some of the other text, is doing this to, but I forget which phrases
> they are. The high score table is not affected.
>
> If I coin up the game, the game plays and displays perfectly.
>
> Self test reveals no errors or problems.
>
> As soon as the game goes back into attract mode, I get this crazy text
> problem. When the machine is in self test, I also have the text problem
> with the game difficulty setting and number of ships per game.
>
> Because the game works correctly in game mode, it seems that I can rule
> out the possibility of a faulty analog output stage. Seems more like a
> digital problem. As I said, everthing checks out in self test, so if
> you can believe that information, then the mathbox is OK, and the game
> code is good, and the rams are good. Aiyee.. still seems like a ram
> problem to me, but I'd like to believe the self test knows what it's
> doing!!
>
> Anyone have some ideas of what I might be looking for?
>
> Thanks for any input. I'll have to check Nick's Tempest troubleshooting
> page next, but I don't remember reading anything about this type of
> problem there, but it's been a while.
>
> Joel-

Sounds like something with the Scaling circuitry. If the scaling is
screwed up at one particular setting (in this case the scale commonly
used by the text), then the invisible line that is drawn from the center
to the point where the text will start will also be proportionally
wrong.
  So. If your "game over" text normally would appear like this..

         ______________________
         | |
         | |
         | |
         | |
         | | "c" denotes center of screen
         | c |
         | |
         | Game Over |
         | |
         | |
         | |
         |_____________________|

Now if the problem is indeed in the Scaling circuit you would get a
screen that looked like this.

         ______________________
         | |
         | |
         | |
         | |
         | | "c" denotes center of screen
         | c |
         | |
         | |
         | |
         | |
         | GAME OVER |
         |_____________________| Where the distance from "c" to the
"g" (in game over) is proportional to the size of the "game over" text.

I would check the IC at location K8 (LS175) and L8 (LS191).
 jess

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