Re: asteroids screen problem (a dead zone)

Could it be the spot killer kicking in when it's not supposed
to? I had a similar problem on an Asteroids once...I knew it
wasn't a board problem because it worked fine with another
monitor.

On Sunday, May 12, 2002, at 09:47 AM, Phil Morris wrote:

>
>> 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 17:27:48 2002