Re: asteroids screen problem (a dead zone)

>There's no distortion in the vectors even as they drift into the dead
>zone. It's almost like playing the game with a piece of black electrical
>tape stuck to the middle of the screen.
>
>Anyone got any ideas?

I have ideas, but they might not be the right ones. ;-) Others here may
disagree with my diagnosis, but there's no harm in trying. :)

First things first - are you certain that it's the board at fault and not
the monitor? For example, either try another board (or monitor) then verify
accordingly.

Also, if you have a dual channel scope, hook up the probes to the X and Y
Output test points on the board, put the scope into XY mode and see if the
problem shows up there.

Assuming that it's the board and not the scope, have you tried putting the
board into test mode? If so, are there any tones to indicate vector RAM
errors? (try pressing the reset button on the board - often tones can go
unheard when simply powering on the board).

Whatever, the problem is with the X output circuitry - it's worth checking
out the AD561 DACs, etc and maybe also the X position counters. Easy enough
to compare the X circuitry to the Y and note any differences.

Let us know how you get on, as the information gleaned could be added to
the Asteroids Troubleshooting Encyclopedia at:
http://www.ionpool.net/arcade/asteroidtech/asteroidsrepair.html#V1

Phil

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Received on Sun May 12 09:49:40 2002