Tech: asteroids fault

[Zektor]

[uk-vac] Tech: asteroids fault
Ok I have an asteroids PCB that has a strange fault. On power up the game
boots fine and will sit in attract mode for a while and then Atari logo
starts stretching out across the whole of the screen for 10 seconds then
goes back to normal for 20 seconds and then strange for 10 seconds and so
on! anyone had this happen before? I thinking maybe a bad rom but the self
test passes

 

[guddler]

What does the test pattern do if left on like this?

I find the test pattern a better tool for judging whats going on as it's
easier to see if it's horizontal or vertical issues (should that be
relevent).

My first guess would be to look at the chips involved in the scaling
circuit since there are so few of them, but i'm not entirely convinced of
that since you say it goes across the whole screen.

Test pattern may be your best friend here!

Martin.


AnDyC2010-06-28 14:07:18

 

[Zektor]

Re: [uk-vac] Tech: asteroids fault
Sometimes it just resets (beeps) a few times and others like now it will sit on the test screen for ages with no problems

 

[guddler]

Yeah, the scaling circuit, but the scaling circuit shouldn't reset the
board.

The scaling signals are produced by the data latch at K7 so start there but
it may be the data that's getting to K7 rather than what's coming out, or
the signals going together to make up the clock for the latch?

If it were me I'd use that as a starting point.

Of course, it sounds like your problem may be made worse by it being
intermittent. Freeze spray perhaps?

Have you tried changing the socket on the Vector rom? Atari sockets are crap
and I believe the data coming from there could effect this latch and in turn
the scaling? That's a bit more of a guess though!

Martin.


AnDyC2010-06-28 14:07:07