TECH space invaders

[MarbleMad]

[ukvac] TECH space invaders
Problems with a 3 board taito space invaders part 2 colour.

On testing the board it worked 1st time BUT unfortunately the 2nd time I
tested it, it was broken

Powers up perfectly when I 1st tried it so I unplugged it and tried it
again a few seconds later - totally scrambled. 2 big red bars down the
screen or just a jumble of messed up test and invaders.

THe unny thing is I think this is what it was doing when I last looked
at it some months ago... I suspect if I try it in a few hours it'll work
again then stop working if I turn it off and on

I suspect it's the bottom board.
Just wish I knew what would cause an intermittent fault like that.
Anyone got any ideas what may be going wrong?
---
James G Watt
http://www.kinetic-arts.co.uk
Part of the Video Arcade Game Collectors WebRing.

You are in a maze of twisty little passages, all alike.

 

[P-Man]

Re: [ukvac] TECH space invaders
> Problems with a 3 board taito space invaders part 2 colour.
>
> On testing the board it worked 1st time BUT unfortunately the 2nd time I
> tested it, it was broken
>
> Powers up perfectly when I 1st tried it so I unplugged it and tried it
> again a few seconds later - totally scrambled. 2 big red bars down the
> screen or just a jumble of messed up test and invaders.
>
> THe unny thing is I think this is what it was doing when I last looked
> at it some months ago... I suspect if I try it in a few hours it'll work
> again then stop working if I turn it off and on
>
> I suspect it's the bottom board.
> Just wish I knew what would cause an intermittent fault like that.
> Anyone got any ideas what may be going wrong?

SI is weird.. the watchdog is really slow, like it kicks every 1.5 seconds,
unlike nrmal watchdogs, so often, you turn on an SI and get a screen of
garbage, you have to wait 2-3 seconds before anything happens.

If you are testing this pcb in a real cab, then you must check the reset
line on the edge connector, if the power supply is doing weird things, it
will mess with the reset line and the pcb will not boot.

If the reset line is beahving properly, and the inverters and stuff that the
signal passes through on the top board onto the cpu board, then start to
look at the roms on the bottom pcb.

Andy