1980 Defender Trouble Shooting Question.

Archived from groups: rec.games.video.arcade.collecting (More info?)

Now that I have a joust machine, I finally got to test a defender board
set I bought many years ago. It was dead, but I soon found that the
main board to rom board ribbon cable had two bad lines and squeezeing
the connector in a vise to reseat the connections fixed that.

The only problem now is two bad video scan lines that appear at the top
of the screen above the "scanner box" (see screen shot). I'm stumped on
what would cause this. Why just two lines at the top?
I checked the theory of operation, but did not see any section that
would cause just this. Any help or comments would be appreciated.

Thanks Ron.


Here is a screen shot.
http://www.mk64.com/ron/line.jpg

Archived from groups: rec.games.video.arcade.collecting (More info?)

Looks great! Now just adjust the monitor's horizontal width so they are
off of the screen.
~eric

Red_Dog wrote:
> Now that I have a joust machine, I finally got to test a defender board
> set I bought many years ago. It was dead, but I soon found that the
> main board to rom board ribbon cable had two bad lines and squeezeing
> the connector in a vise to reseat the connections fixed that.
>
> The only problem now is two bad video scan lines that appear at the top
> of the screen above the "scanner box" (see screen shot). I'm stumped on
> what would cause this. Why just two lines at the top?
> I checked the theory of operation, but did not see any section that
> would cause just this. Any help or comments would be appreciated.
>
> Thanks Ron.
>
>
> Here is a screen shot.
> http://www.mk64.com/ron/line.jpg

Archived from groups: rec.games.video.arcade.collecting (More info?)

ND <aaaa@sss.com> wrote:
: Completely normal. Programmers for that game ran tight on memory for
: variables, so they decided to use a bit of off screen video ram as a
: scratchpad. You can find references to it in google. You should be able to
: adjust it off the screen using you monitor controls.


There is no memory on the early williams games, other than the screen ram,
so the holes are all that's available for program ram

It's just a bug in the decoder proms, that a little bit of the program
ram shoes up on the the screen.

--
Mark Spaeth mspaeth@mtl.mit.edu
50 Vassar St., #38.265 mspaeth@mit.edu
Cambridge, MA 02139
(617) 452-2354 http://rgvac.978.org/~mspaeth

Archived from groups: rec.games.video.arcade.collecting (More info?)

"Red_Dog" <ron347@yahoo.com> wrote in news:1125887619.010416.271770@f14g2000cwb.googlegroups.com:

> I never would have found nothing wrong by myself.
> Its interesting that MAME doesn't faithfully show the lines.
> On second thought , I'm glad it does not.

I had wondered about that since this posting, so I asked.

http://www.mameworld.info/ubbthrea [...] 1125979760

It's done so bug reports are at a minimum. How about that.
--
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