Weeeeird Tempest problem
Gregg Woodcock
> By swapping boards with another boardset, I isolated the problem to the
> main board. This main PCB still produced the weird display when I
> plugged in a known-good mathbox board.
> The data from the EPROMs on the main board matches the data from a
> known-good set.
> In test mode, this boardset displays "M" for a split second, but quickly
> erases it, apparently deciding all is well.
> Everything else about the board works perfectly.
> OK, so I haven't dug into the schematics yet to hunt down the source of
> the problem. I admit it. But I want to know if anyone else has ever seen
> a problem like this, and, if they have, can they save me some work and
> tell me which IC has flaked out.
> I imagine the key to the puzzle is that only three objects appear to be
> affected-- are these objects processed exclusively by one chip or one
> group of chips?
The Tempest (and other Atari) boards frequently suffered from bad
solder joints. The flickering "M" in test mode is very likely a bad
connection on one of the pins on the interboard connector. Resolder
all pins on the main board. If that doesn't help, then the problem,
to me, sounds DAC related in that perhaps some low order bit(s) of the
digitial inputs are shorted low.
--
THANX...Gregg day 214.684.7380 night UNLIST/PUBL TEXAS NOT CANADA!
wood...@bnr.ca or wood...@nt.com or bn...@cleveland.freenet.edu
*CLASSIC VIDEOGAME COLLECTOR BUY/SELL/TRADE NON-COMPUTER (ARCADE/HOME)*
"If you quote me on this I'll have to deny it; I won't remember because
I have such a bad memory. Not only that, but my memory is *terrible*."
David Shuman
I have a Tempest board that works great except for one small detail. It
seems to have a problem scaling certain objects. Specifically, three
objects:
1. Tankers.
2. The big, phosphor-burning word "TEMPEST" in
the attract mode.
3. The stars that appear when you zoom from one
level to the next.
As tankers emerge from the center and move outwards towards the rim, they
go through discrete changes in size, maybe five or six total between the
center and the rim. Normally, of course, the change in size is linear,
and indeed, this board displays spikers, flippers, etc. as it should.
The problem with "TEMPEST" is similar to the tanker problem. Instead of
increasing in size gradually, it grows (and moves up the screen) in
steps: first small, in the center of the screen, then suddenly bigger,
a bit higher up, then it jumps a bit higher still and appears at full
size.
Between levels, the starfield appears almost static, i.e., the little
twinkles barely move as you zoom past them. Though the similarity isn't
obvious, I imagine this effect is caused by the same glitch as the first
two symptoms. The starfield doesn't look like a single object in the same
way that a tanker or "TEMPEST" does, but turn up the brightness so you can
see the "invisible" vectors, and you'll see the stars are bright points on
a spiral-like shape that, like other objects, gets scaled (or doesn't, in
the case of this particular board).
By swapping boards with another boardset, I isolated the problem to the
main board. This main PCB still produced the weird display when I
plugged in a known-good mathbox board.
The data from the EPROMs on the main board matches the data from a
known-good set.
In test mode, this boardset displays "M" for a split second, but quickly
erases it, apparently deciding all is well.
Everything else about the board works perfectly.
OK, so I haven't dug into the schematics yet to hunt down the source of
the problem. I admit it. But I want to know if anyone else has ever seen
a problem like this, and, if they have, can they save me some work and
tell me which IC has flaked out.
I imagine the key to the puzzle is that only three objects appear to be
affected-- are these objects processed exclusively by one chip or one
group of chips?
--
--Dave--
John Keay
> > By swapping boards with another boardset, I isolated the problem to the
> > main board. This main PCB still produced the weird display when I
> > plugged in a known-good mathbox board.
>
> > erases it, apparently deciding all is well.
>
> ........ If that doesn't help, then the problem,
> to me, sounds DAC related in that perhaps some low order bit(s) of the
> digitial inputs are shorted low.
It does (sort-of) sound like a low order bit digital to analogue problem,
but I doubt it because both X-axis and Y-axis DACs would have fail the
same way. Do the tankers move smoothly along one axis and in steps along the
other? I guess not from your description.
I also think a bad solder joint or wire would be the first thing to try.
After that I'd look for a faulty chip on the main board that
interfaces the board to the math box. Or maybe a slow chip in the interface
logic (that might explain the split second "M" failure).
* John Keay ! TMS320C80 design *
* work: ke...@tiuk.ti.com ! Texas Instruments Ltd. *
* home: jo...@keay.demon.co.uk ! Northampton, U.K. *
* Disclaimer: All opinions expressed herein are personal. etc etc *