Hi all,
I've got an Asteroids board that worked properly for a few hours since i've owned it before crapping out on me...
The board is constantly resetting, with some sort of pulsing running through the audio & vector system.
If I flip the game between play & test mode quickly i can usually
see the attract screen for a brief period before it starts off
resetting.
See below of a video of the screen when running in test mode, the audio
& pulsing of the vectors are in time with each other. When the game
is in Normal mode you get a similar pattern to test mode, but it move up
and off the screen after a few seconds and it looks like you're looking
at a blank screen.
Monitor output
Logic probe showing CPU reset
Following some tidbits of info from the forums and web if I isolate the
DMAG0 signal from the 74LS42 @L6 the game will play blind (even though
the audio sounded a bit quiet) and the reseting stops on the CPU.
This puts the fault in the Vector state machine are i believe.
If I remove the Prom @C8 the pulsing still shows up, but if i take out
either of the LS08 @E6 or B8 it disappears. They were already in sockets
along with quite a few other IC's this board, its had a tough life!
Any pointers about where look or what i can try would be apprecieated, I've been round in
circles this afternoon trying to find where this pulsing is coming from
but can't seem to find it .. yet
Many thanks, Mart.
I've got an Asteroids board that worked properly for a few hours since i've owned it before crapping out on me...
The board is constantly resetting, with some sort of pulsing running through the audio & vector system.
If I flip the game between play & test mode quickly i can usually
see the attract screen for a brief period before it starts off
resetting.
See below of a video of the screen when running in test mode, the audio
& pulsing of the vectors are in time with each other. When the game
is in Normal mode you get a similar pattern to test mode, but it move up
and off the screen after a few seconds and it looks like you're looking
at a blank screen.
Monitor output
Logic probe showing CPU reset
Following some tidbits of info from the forums and web if I isolate the
DMAG0 signal from the 74LS42 @L6 the game will play blind (even though
the audio sounded a bit quiet) and the reseting stops on the CPU.
This puts the fault in the Vector state machine are i believe.
If I remove the Prom @C8 the pulsing still shows up, but if i take out
either of the LS08 @E6 or B8 it disappears. They were already in sockets
along with quite a few other IC's this board, its had a tough life!
Any pointers about where look or what i can try would be apprecieated, I've been round in
circles this afternoon trying to find where this pulsing is coming from
but can't seem to find it .. yet
Many thanks, Mart.
