Asteroids and 'wiggly' diagonal lines

After looking at loads of web sites and reading old messages, I have some
possible theories as to what is causing the 'wiggly' diagonal lines on my
Asteroids game. However, all the descriptions I have seen don't exactly
match the fault with my particular game, as in one place in particular the
lines are even more 'wiggly'!. Vertical and horizontal ines also look
slightly 'bitty' as every other 'pixel' (I know, they're not pixels!) there
is a lighter one, so giving the bitty appearance. Some possible causes I
have seen mentioned are bad DACs, noisy power supply (I've recently
replaced 'Big Blue' in the PSU, but haven't yet replaced the large blue
caps in my G05-801's regulator board - they're on order), bad edge
connector contacts (???) and possibly even the second or third stage
transistors (that includes the MPSU57's, MPSU07's, etc and the larger
2N3792's and 2N3716's on the large heat sink). Adjusting the linearity pots
on the deflection board does not help the wiggly lines problem.

So I'm scratching my head a bit, tempted to tackle the possible solutions
one by one, well aware that *neither* could be the cause of the problem,
but at the same time thinking I should at least ask the experts here to see
what they think. And no, I'm not being lazy either, I've spent many hours
reading up and trying to suss this out, but my limited (but slowly
expanding) knowledge doesn't exactly help.

As they say, a picture is worth a thousand words and maybe I'm
'mis-reading' or even mis-reporting the fault, so here's a picture of the
game in test mode:

http://www.morris0.fsnet.co.uk/Test_Mode1.JPG

Note: it's 700K! Also, I've since adjusted the linearity pots on the
deflection board so the top triangles are now more even.

I'm afraid the picture is a little blurred - that's the camera/my
photography but it's the best of the bunch, the actual display is much
sharper. Even so, it's good enough to see the wiggly lines I think. Oh, and
the coloured areas are reflections. :)

The most interesting segment is the intersection of two diagonals just
below the 'brightness' test lines in the centre of the display - this
intersection results in a far more major 'wiggle' - looks like someone was
drawing and the pencil slipped to the left a couple of times! The ship also
has a very short (about 2 or 3mm) horizontal line sticking out of it's nose
if I point it directly left or up/down a little from there.

I've also noticed that while playing a game, at certain screen areas, if an
asteroid explodes then it can sometimes generate a few extra but extremely
brief horizontal or vertical lines, maybe up to a an inch or two long. This
is very intermittent though.

Some other points worthy of note re the picture:

The edges of the picture look *FAR* more 'bowed' than they really are
(they're really fairly straight), but having said that, there is a *little*
pincushioning, slightly inwards on the left vertical line (and more so
towards the top left hand corner), and a very slight upwards bowing on the
topmost horizontal line.

There is also a noticeable curve downwards and to the left in the
horizontal plane from about the centre of the screen and to the left of it,
increasing towards the left edge. The right hand side looks fine. This is
more noticeable on the player 1 score and the text that appears asking for
your initials to be input.

As I mentioned, I have since adjusted the linearity pots and the elongated
diamonds on the top half are now somewhat less elongated. The worst
distortion was in the upper left corner and there is still some there,
despite adjusting the linearity, but all corners were affected to some
degree. When playing the game this was manifested by, especially in the top
left corner, any objects entering any corner or going off the top or bottom
(but not left or right edges) becoming noticeably stretched vertically.
It's improved now, but still not perfect. Sorry, I couldn't get a decent
picture of this.

Also note: the fine vertical lines in the area of the I I and the zero's
are fine scratches on the surface of the tube. It was like that when I got
it. :(

Thanks for any help you can offer,
Phil

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Received on Sat Jan 12 14:08:54 2002