Re: Asteroids CPU repair problems

To answer a couple of questions at once:
John wrote:
>What are the symptoms currently? Do the 2114's run hot? I just replaced
>ALL of them on an Asteroids board, and it worked aftword. They were ALL
>dead! Only other problem with the board at that point was a bad 74ls174
>for the thump thump sound...
>Have you built a NOP for that cpu? Then checked with a scope for proper
>address count?

Yep. Replaced them. It's funny you should mention them, it seems to me
also that when one of these goes (beep beep, boooop!) they all go also! I
assume that you are talking about the 4 vector RAM chips. Strangely, I
don't normally see the program RAM chips (the two in the first row) go bad
as often...

Now this NOP thingy you speak of. Nope. Haven't built that. Probably
should if I knew what one was... So! If you could give me an idea of what
to do with one, I'd be VERY interested in hearing about it.

I've replaced about 18 chips in the board now, and still haven't found the
problem. I KNOW it's a watchdog problem, but can't seem to nail it down
it's almost like the system is too SLOW to stop the count, not that it
doesn't try to...

Say THANKS for the thump thump sound chip hint. Could you tell me
what chip location that one is?

Joe wrote:
> What's wrong with it?
Busted. Fragged. Bad Watchdog circuitry.

> Does it beep at you in self-test mode?
Nope. Doesn't do even that.

> If it doesn't, check/disable the watchdog reset circuit and see
>if things get better. The ROMS, especially if they're masked ROMS,
>tend to go bad on the old Atari B/W XY stuff.

Tried that. Disable the watchdog, and the thing squeels at me, while
the LED on the monitor stays lit. It seems to be a bad vector engine.
Checked the ROM's, they're OK...

> No. I've said it before, and I'll say it again: If someone
>will build the switch PCB, I'll do the logic PCB. So far there've
>been no volunteers. The switch PCB is NASTY, and I'm not going to get
>stuck doing it too. People were talking about building a PC interface,
>which I think is the way to go (unfortunately, I know nothing about using
>the Serial/Parallel ports of a PC, or about writing software for PCs)

OK. ok. what's the switch PCB, maybe I can get involved. <sign> "just
a minute dear, I'll be right up..." heh-heh-heh, my poor wife!

Ace
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Received on Tue Jul 7 14:26:43 1998