Re: Help with Dead Gravitar Board

First make sure that your processor has a valid clock signal (look at
with an o-scope or logic probe). Then make sure that the reset line is
properly going low and then staying high after powerup. Make sure the
reset line does not pulse. That means that the watchdog circuit is
barking and means that you have an issue with the main address decoder,
adddress line buffers or data buffers. Actually, you need at least one
ROM working as well (look in the manual for the ROM that is required for
self test to work).

If the board is old, then your crystal may be damaged, it is common for
them to get beat up and broken. It is the little metal can. They cost
like a buck and you won't have a valid clock signal if it is jacked up. :-)

check that out if you can and report back.

jess

Malcolm Mackenzie wrote:
> Hello all. New subscriber here. Finally got my first vector game
> (Space Duel) and have really been enjoying it. Inspired me to get
> some more. Thought I'd introduce myself and pose my first questions.
>
> I recently bought an "untested" Gravitar board and of course it was
> dead. I have been testing it in my Space Duel. Initial, and current
> symptoms are:
>
> No game sounds (game doesn't play blind)
> No video, Spotkiller on
> Both Game start and Game select LEDs on (not flashing)
> Self test sometimes results in 2 tones, sometimes not
> Sometimes, for unexplained reasons, the coin solenoids will chatter
> when the game is powered up
> Tried grounding the watchdog to see if the self test would operate
> with no effect
>
> So far I have:
>
> Reseated the ROMs
> Tested the custom chip (it works)
> Replaced the 6116 RAM
> Replaced the Pokeys
> Replaced the processor
>
> All of this has had no effect on the performance of the board. I was
> thinking I'd check the ROMs next. The board has a repair in the XY
> output section where two of the four 1495 chips have been socketed. I
> tested the repairs and they seem to be ok. I don't have any 1495
> chips to test to see if these are the problem. Since the board seems
> to be resetting constantly, I'm figuring this isn't the main problem.
>
> This is the first Atari board I've ever worked on. Anyone have any
> specific suggestions for me? Where should I start with the logic
> probe? Thanks for any and all help. -Malcolm

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Received on Sat Jul 22 02:47:29 2006