RE: Tempest Tech Perfect self test, but strange vectors in gameplay

If I had to guess, it sounds like the AVG stack registers (or something
associated with them) aren't working properly. That area of the design is
essentially the same as the DVG. That's one of the weakest aspects of the
self test - lots of problems can go undetected. They load up the display
list with JSRs, but they use relatively low address values instead of having
it span a large portion of the vector RAM. I've seen cases where the
registers work fine at the low addresses (i.e. self test), but not the
higher addresses (i.e. attract mode). Might be time to break out the logic
analyzer, if you haven't aready.
 
Of course, it could be something entirely different.
 
Alex

----
ayeckley@elektronforge.com
www.elektronforge.com 
________________________________
	From: owner-vectorlist@vectorlist.org
[mailto:owner-vectorlist@vectorlist.org] On Behalf Of Malcolm Mackenzie
	Sent: Saturday, August 29, 2009 10:28 AM
	To: Vector List
	Subject: VECTOR: Tempest Tech Perfect self test, but strange vectors
in gameplay
	
	
		So... Yet another Tempest post.  I have a Tempest board that
I've been fighting with for a while.  Came to me Dead.  I've replaced most
of the RAM and the ROMs as well as making sure the AUX board and
interconnect cable are functioning correctly.  
	 
	It's up and running now.  Passes self test and displays all the
selftest screens beautifully.  When I switch to game mode, however, the
display flashes odd looking, large vectors and some of the sprites look odd,
but the text looks great.  After a few seconds of flashing, the spot killer
comes on and the screen goes black. 
	 
	Anyone have any ideas?  I'd say I have a problem with vector
scaling, but then why isn't the text  or the self test affected?  Are the
game vectors and text handled by different areas of the board?  Thanks for
any and all help. -Malcolm
		
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