Asteroids - getting there...

Hello guys,

I have een working for many many hours on my Asteroids board since I last asked
you guys. I have made some good progress. First, the board was dead, watchdog
resets happening. After replacing one 2114 RAM and all LS157 data switches (all
were or went bad) The board played well, even video output, altough it was
distorted (jagged X output).

After replacing one LS374 latch, LS157 selector and analog parts in the X
counter section, the output is clean... but now the board is caught in a loop
and draws the same random vector over and over as can be seen in the following
link:

http://www.mypearl.dds.nl/Asteroids/Asteroids_large.mpg (1.3MB)

or

http://www.mypearl.dds.nl/Asteroids/Asteroids_small.mpg (135 KB)

As you might be able to see from the screenshot, a lot of sensible things are
displayed: Atari copyright notice, Insert coins, the saucer, your spaceship,
the test screen and some moving asteroids (all togheter!).
Depending on the coin DIP switch settings and language the displayed images are
different!

The weird thing is, in TEST mode EVERYTHING is okay! No RAM/ROM errors, no
distorted vectors... Just as if there is no problem with the board.

I have checked all logic signals (even all unnamed TTL inputs and outputs) in
the Vector Generator logic (sheet 2A). All signals are alive, except
for '/DMACNT', which is decoded directly from the MPU address bus by L6. It is
always high. Replacing L6 does not fix it. Could this explain why I am getting
this? What is the /DMACNT used for?

I really hope you guys can set me back on the right track... would be eternally
grateful! :)

Cheers,

Mendel

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Received on Wed Jun 25 09:40:16 2003