Vectorlist Archives: RE: Tempest CPU problems...

From: Evrovski, Andrew <andy_at_cyberplex.com>
Date: Mon Apr 22 2002 - 12:59:32 EDT

Well, don't know if this will help (and I didn't experience the same
problems that you have had), but you may want to try replacing the
transistors in the scaling circuit (Q11 & Q12) 2N3906, 2N3904.

I had some bizarre scaling and text problems as well and replacing those
fixed it.

Good luck and be sure to let us know how it turns out.

Andy

-----Original Message-----
From: TomWiz [mailto:twisnion@enteract.com]
Sent: April 22, 2002 13:47
To: Vectorlist
Subject: VECTOR: Tempest CPU problems...

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

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