Battlezone board -- mountains extend too far in negative direction

Finally getting back to this Battlezone. Last party, it started acting up
with intermittant mathbox errors, shrinking screen, and a very dim
background.

This afternoon I resoldered the interconnect header pins again. It looks
like last time i just reflowed them, and the old flux caused problems again.
Wicked out all solder, resolderd, seems good now.

Also, the 8023E at B/C2 looks like it's pins tarnished. I've cleaned it, and
while it still doesn't look good, that cleared out the last of the mathbox
errors.

The background still disappears however (mountains, tanks) while the text
and gun-site are still visible, and self test looks fine. Next step was to
hook up a scope.

Here is where things get weird. Even with a Z input, my scope doesn't seem
do intensity, just kills some retrace, so everything is there. What is
immediately noticeable is that, even with the test screen centered, the
mountains extend much further in the negative X direction than in the
positive, and at the extreme, there is even a verticle line as if it wanted
to be further negative, but those values are collapsed.

To put some numbers on it: With my scope on 5v/div, the self-text box
extends about +/- 8.5 volts. Switching to game mode, the gun site is
centered, the mountains go to +9 v and down to -14 v. The B&W vector FAQ
calls the X limit +/- 10v, so this sounds very wrong.

If this was an analog problem, I would expect the the whole screen to be
stretched in the negative direction, but the text and self-test are
symetrical. The tanks may every well be extending to far too, but it's hard
to tell since they move around. :-)

So now I'm stumped -- is this even a probem, a mathbox issue ? Where to look
next ?

==========================================================
Chris Candreva -- chris@westnet.com -- (914) 967-7816
WestNet Internet Services of Westchester
http://www.westnet.com/
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Received on Sat Jan 31 18:03:07 2004