Re: Few Space Duel/Gravitar questions.

andre wrote:
> I have 3 Space Duel boards, with 3 issues..
>
> pcb 1) Has no life.. the -28 volt pin only reads about
> half of that.. The 555 is new and both diodes beside
> it test fine. There isn't much else in this circuit..
> the electrolytics are new as well.. Any idea on what
> else could cause the low reading? Can I replace the
> 100 volt, type 100 or whatever they call it diode with
> a 4xxx series?
>
I don't believe that the -28V effects anything except the EAROM so this
shouldn't keep the board from dying. All you should need is a solid +5V
and the 10.3V to get the logic up and running. You need the ±22V and all
related voltages out of the regulators for the DAC's and sound. Make
sure you have those and then you should checkout the reset pin on the
CPU. Make sure it is low then stays high on powerup. If it is pulsing,
then you have a watchdog barking, tie WDDIS to ground and see if you can
get a display to give you error codes in self test. If the 10.3 is there
and reset is behaving, make sure you have a solid clock (is it 12MHZ on
SD?)... check on the main 12M test point to make sure it is there. If
not, your crystal is most likely yanked or cracked (very common).
> pcb 2) Has no life. The first eprom pulses fine, but
> none of the other ones have any pulses on the pins. I
> replaced the 244 immediately after the processor and
> that did nothing. Even if the eproms were bad, it
> would still pulse correct? (I am sure they are ok
> though) What would cause only all the eproms after the
> first one to be dead? The connections are fine as I
> traced the pins for continuity..
>
>
Check the stuff for above first and get a baseline. Then, I generally
start by probing each address pin, you cant guarantee that they will all
be pulsing because the program might be in a tight loop where it is only
cycling the bottom two address bits. The lower ones should all be
pulsing tho. Take out all the EPROM's on the CPU side except the top
Address one (that is where Atari generally puts the Self Test routine),
you can tell which one that is by looking at the owners manual and of
the ROM's will have an * note saying that this ROM must be functional
for self test to run. What you are doing is eliminating possible bad
IC's that aren't 100% required for Self Test. Now, look at the data
lines on the CPU, they should *all* be pulsing, if not you might have a
shorted buffer or a shorted RAM holding one high or low. While you are
at it, swap the CPU with a known good one to be sure yours is good (dont
bend pins or you start to get into chip swapping hell). :-)

> pcb 3) This board seems to work fine.. but the objects
> flying around, or even your ships, sometimes shifts up
> and down very slightly..but nothing else. I know on a
> Star Wars a bad prom can cause only 'certain' vectors
> to flake out while not affecting the rest, but on a
> Space Duel what would cause that?
>
A failing Y counter on the lower bits might cause this. Not quite sure
the best way to troubleshoot tho.
> And one Gravitar...
>
> This one is pretty odd.. the pcb works fine.. Only
> issue is if you shoot one of the red flying craft on a
> planet, or tractor fuel, the sound for the reactor
> (that you shoot in the reactor planet) will play
> forever until you die or leave planet. The tractor
> beam sound is there..but not the beeping of the fuel
> you are picking up.. If you explode, there is no
> explosion sound..but everything else explodes fine.
> Self test shows nothing wrong and both pokeys were
> swapped out.. and nothing.. any ideas?
>
>
Hmmm... that *is* an odd one. Look for cut or shorted traces due to
excessive PCB piling and abuse... you might be getting a really odd side
effect of a pokey addressing issue maybe? The solder on the Atari PCB's
is prone to being scraped and creating a trace short. I have seen really
odd effects by random shorts and cuts on the PCB's. Otherwise, make sure
the pokey address decoders are looking okay.

hope that helps or at least puts you on a new set of wild goose chases. :-)

jess

> Thanks in advance.
>
>
>
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Received on Tue May 6 02:19:08 2008