Re: Tempest CPU problems...

6502a NOP and signature analysis?

TomWiz wrote:
>
> Guys,
> I'm looking for some opinions on repair paths for a Tempest
> boardset
> that is driving me nuts. Here's the history.
>
> Boardset was in cab that was exposed to water. Board is clean,
> but dirty.
>
> Initial power up, boardset dead.
> Several Roms had oxidized legs, replace roms, board now boots to
> ram errors.
> All roms good, supply good.
>
> After fighting with the RAM errors (5 Bad Rams total, 4 Vector
> Rams, 1 Pgm Ram)
> game now boots clean but no XY Output.
>
> Digging into XY Output stages and found +15 regular went nuclear
> at one time,
> working from the bottom up, ended up replacing every (ouch)
> component that
> was on the +15 line. I now have clean vector output on scope,
> time for the
> monitor connection.
>
> Mathbox tests reveal two bad pokey's, replaced them. Now no
> errors on
> any test (Slam etc. Test screens are perfect.
>
> BUT, during intro screens I have some oddities.
>
> A. High score display is showing.
> 1. Jim
> 2. joe
> 3. tom
> 4+5.&^%% (This line has score 4 and 5 superimposed on each
> other.)
> blank line
> 6. bob
> 7. you
>
> B. Intro screen where Tempest grows from center has two Tempest
> logo's that
> grow in sync (kinda cool) until approx center of screen, then you
> get one as
> normal. As they grow, they correctly have the color 'sub logos'.
>
> C. During game play, the Green Spikes will 'Sometimes' start off
> at the wrong
> spot and move at odd angles. An occasional object will jump out
> of the tube
> and then back in. You can still shoot the items like there were
> in the tube,
> so that leaves me to believe that Ram has the correct object
> positions reflected.
>
> A known good mathbox was swapped in, no change.
>
> I've gone thru with a Huntron Curve tracer the vector pgm
> counter, buffers
> and a few of the VSM chips, and nothing was out of line. But I
> didn't expect
> I would find anything with the tracer with this type of failure.
>
> I've checked the archives, and there was one other person with
> the
> similar problems that posted, but there were no public replies. I
> know I've
> seen this before on the list...
>
> So, with all of that said, can any experts to the inner workings
> of the
> CPU point me to an area that might be worth investigating. I hate
> using
> the 'Brute force method' of just replacing stuff without a
> direction...
>
> Thanks
> TomW
>
> ---------------------------------------------------------------------------
> ** To UNSUBSCRIBE from vectorlist, send a message with "UNSUBSCRIBE" in the
> ** message body to vectorlist-request@synthcom.com. Please direct other
> ** questions, comments, or problems to neil@synthcom.com.
---------------------------------------------------------------------------
** To UNSUBSCRIBE from vectorlist, send a message with "UNSUBSCRIBE" in the
** message body to vectorlist-request@synthcom.com. Please direct other
** questions, comments, or problems to neil@synthcom.com.
Received on Mon Apr 22 10:19:08 2002