Tech: Battlezone graphics problem

[Guest]

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

Hi all, I've got a wierd problem with a Battlezone board and I wondered
if anyone had seen a similar issue before. The screen is squashed
over on the right hand side of the monitor and any text is illegible.
So far I've;

1) Confirmed the monitor is OK.
2) Ran self test - no beeps or boops
3) Tried another working aux board.
4) Confirmed all the ROMs are OK and being read properly.

Pictures of the wierdness are at;

http://www.dannypearson.com/bz1.jpg
http://www.dannypearson.com/bz2.jpg

Any help appreciated!

Danny

 

[Guest]

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

Mathbox is my guess.

 

[Guest]

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

Oh, something else to do (have fun... muahahahaha).... replace ALL of
the ROM sockets. Atari factory sockets are notoriously shitty. I was
having some weird problems with my BZ many years ago, and after some
research, replaced the sockets. It was fine after that for years
(until a certain somebody-who-will-remain-nameless tested his boards in
my cab and somehow haunted it).

That being said, TAKE YOUR TIME desoldering and removing the old
sockets. It is almost comically easy to gank traces off these old
Atari boards.

Good luck,
Rob

 

[Guest]

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

>Hi all, I've got a wierd problem with a Battlezone board and >I
wondered if anyone had seen a similar issue before

Unplug mathbox from harness and MPU
Start up game and go in test mode.
Start there- get good test pattern and no errors.

Once that works you can move on to messing with the mathbox.

Kirb

 

[Guest]

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

DanP <dannypearson@hotmail.com> wrote:

: Hi guy thanks for the quick responses. As I said I've tried using a
: known working AUX board (that has the mathbox on it) and no change.
: I've also totally disconnected the AUX board, afaik the Vector
: Generator board should display an image fine without it, just no 3D
: objects. It still looks the same with the odd rhomboid shape. So
: from that I've eliminated the AUX board (aka mathbox) for now.

OK, you've eliminated most of the digital points of failure, that leaves
analog. The BattleZone generate has a good number of analog parts that can
fail and do weird things.

First - put it in self-test mode, and see what that gives you. It is far
easier to judge from the static picture. However, what your picture shows
doesn't really look to me like a mathbox error anyway. It does look like an
analog offset problem

Next, go to www.jmargolin.com and download the Secret Life of Vector
Generators - http://www.jmargolin.com/vgens/vgmenu.htm . Print it, read it,
live it. 🙂 OK, you can skip to the part where he talks about BattleZone.

Next, get the schematic and read it, concentrating on the vector generator
section.

BattleZone has a bunch of extra buffers and stuff between the DACs and the
output. You'll see the two DAC circuits doing the output -- and some
spaghetti in the center that looks like a big feedback circuit.

Atari did some wacky analog clipping in this circuit, with the X/Y
values to clip at stored as charges in capacitors, and analog comparators to
the the clipping. The clip-values are taken from the same DACs that do the
output, hence the appearance of a feedback loop. Read Jed's article.

Now what: Well, hopefully you have an oscilloscope, or know where to borrow
one. I usually trace the signal from the output of the DAC to the
test point. Find where it goes bad, and that's the problem.

I'm repeating a lot of this from memory, much of it has been hashed out on
the Vectorlist, searchable archive of which is at http://www.vectorlist.org/



-Chris

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