Fwd: Re: Asteroids MPU troubleshooting

Darn, forgot to change the list name!
.......

>
> Date: Thu, 18 Jun 1998 10:23:34 -0400
> To: vectorlist@spies.com
> From: David Humphrey
> Subject: Re: Asteroids MPU troubleshooting
>
> Whew!  Well, now that that's over, and we're back on-line, let's power up
the
> engines and get back in orbit. 
>
>
> ASTEROIDS!
>
>
> I still need help, and I am willing to offer up some tidbits of recently
> gained knowledge to the database for troubleshooting these boards.
>
> 1) grounding the /VW line (pin 7 of  the '157 at K2), or other RAM address
> select lines, will cause the MPU to generate the beeps that indicate RAM
> failure for one of the RAMs (if it hasn't already).  This is a good way to
> tell how far your board has come up.  If it CAN do the beeps to tell you it
> thinks it has a bad RAM (which you just caused by momentarily  grounding
that
> pin), it is pretty far along.  The ROMs are probably good, the RAMs are
> probably good, and the sound is good (well, OK, that last one is a bit
> obvious).  At this point if you still have the watchdog reset problem, the
> cause is beyond this. (and I'm still trying to figure that out).  Presumably
> it is in the vector generator section of the board.
>
> 2) Grounding the HALT line (pin 2 at L10) will cause the MPU to indicate
> watchdog reset problems in a good board.  This indicates that the CPU is
> looking for that HALT line to continue operation, and if it doesn't get it,
> it doesn't execute that next section of code that will output the watchdog
> timer reset.  So... a bad vector state machine circuit will freak the MPU
> into watchdog reset.
>
> That's where I am now.  I now know I have a bad vector drawing circuit,
but I
> don't know where the problem is, all the signals I have seen look good, even
> the watchdog reset, though it is obvious now that the TIMING of the
signal is
> too far apart to stop the clock before the reset is generated.  Again, I am
> looking for input from people on known problem chips, possible points on the
> board to probe for data, anything to keep quantifying the operation of this
> board.
>
> Thanks guys.
>
>
>
> Ace

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Received on Thu Jun 18 09:26:50 1998