Here's an old post by me - it'll help you isolate either an MPU or VSM problem.
see step 2 below...
Paul
=======================
For Asteroids and Asteroids Deluxe boards with no signs of life:
Unplug the monitor from the harness at it's molex connector to avoid
damage to it - when the monitor sits in spot killer state too long things
can fry!
1. Start out by verifying that the clock is running. (The crystal on
these boards
breaks off WAY too easily.) Then check that the CPU and ROM's are good.
If you found nothing or it's still dead, you've got a watchdog reset
happening - see if pin 40 of the CPU is toggling (it's supposed to be held
high).
2. To figure out who is causing the watchdog resets (the MPU or the VSM
(Vector
State Machine)), take the 74LS42 at L5 (L6 on Asteroids) and socket it,
then
lift out pin 1 to isolate DMAG0.
a) If the board stops resetting, the MPU is not the problem and you
should be
able to play a game "blind" or switch into test mode and listen for any
beeps
indicating RAM/ROM problems. That will at least help you get the MPU side
running properly and then you can play the game blind.
b) A board that is still resetting has a problem with the MPU and also
possibly
the VSM. Check the ROMS, RAM and especially the 74LS245 (or AM83048)
at E2 (E3 on Asteroids). Once you fix the reset problem, switching to
test mode
should reveal any other missed RAM/ROM issues and verify the MPU is
running ok. You should now be able to play the game blind.
3) Place pin 1 of the 74LS42 (DMAG0) back into it's socket. If the
watchdog is
resetting, it's time to look at the VSM side of things. If it's not
resetting, plug
the monitor back into the harness and look for some video.
For the VSM, check the PROM at C8 (C9 on Asteroids) and surrounding state
machine signals for HALT, DMAGO, STOP, GO and the like. The rest is pure
grunt
work to check the state machine is running properly. Someone else please
feel free to add details to the VSM debug procedure...
Paul
"TomW" <twisnion@enteract.com> on 10/31/2000 09:25:56 AM
Please respond to vectorlist@synthcom.com
To: vectorlist@synthcom.com
cc: (bcc: Paul Tonizzo/SYBASE)
Subject: VECTOR: A little Asteroids Board Repair help....
please...
I've got a real strange Asteroids Board that I'm trying to repair that got me
baffled. Here's the scoop, if anyone has any opinions please let me know.
The boardset is a Rev 4, running on the bench.
The board works fine in self test, perfect picture, no errors are reported. In
game play mode, the board watchdogs. In test all switches beep fine, including
Tilt.
If you disable the watchdog, the game still does not run, only a diagonal
line/outline of screen scrolls on screen.
Fluke 9010 unit verifies RAM OK (long Ram test)
Fluke 9010 unit verifies ALL ROMS checksum ok, in socket. (Also using a know
good set, Rev 2)
Manually loading Vector memory with code to generate a + sign, works fine, and
upon a DMAGO, you get a perfect +. All scope sig's that I have for the + match
just fine.
For Kicks, Isolating the L6-Pin1, does indeed put the game into play mode, but
obviously, you get no screen, restoring the connection results in watchdog's.
I've poked around in the VSM and TIMER for 2 days now, and in Test mode,
everything looks fine.
Any suggestions ?
TomW
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Received on Tue Oct 31 10:59:17 2000
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