Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!att!rutgers!cbmvax!hood
From: hood@cbmvax.commodore.com (Scott Hood)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: Jittery A3000 Video
Message-ID: <20300@cbmvax.commodore.com>
Date: 2 Apr 91 22:33:55 GMT
References: <14760@mcdphx.phx.mcd.mot.com> <20144@cbmvax.commodore.com> <1991Mar28.043102.12173@lynx.CS.ORST.EDU> <2709@sirius.ucs.adelaide.edu.au>
Reply-To: hood@cbmvax.commodore.com (Scott Hood)
Organization: Commodore, West Chester, PA
Lines: 36

In article <2709@sirius.ucs.adelaide.edu.au> jpotter@ucs.adelaide.edu.au (Jonathan Potter) writes:
>My 3000 does exactly the same thing - for the first few minutes after bootup
>(when it is cold), random lines will jump left & right.
>
>I have been told that it is a fault Agnus chip, and this seems likely, as it
>only happens when there is actually something being displayed on the screen
>(like text output). It goes away after a few minutes (presumably when Agnus
>heats up) so I assume it is a heat fault.
>
>Try changing the Agnus chip and see if that makes any difference. It doesn't
>bother me all that much as it never lasts for more than 5 minutes at the most.
>
>Jon
>-- 
>| P.O. Box 289     | jpotter@itd.adelaide.edu.au |   spinach...              |
>| Goodwood, SA     | FidoNet : 3:680/829         |                           |
>| Australia  5034  |                             | Sort of green and wrinkly |

I would sugest that you FIRST try the fine tuning adjustment in the
A3000's user manual because I am fairly sure that it is the fine tuning
adjustment that is just on the hairy edge of being stable and not having
any pixel jitter.  This is most often seen at power up when the pixels
coming out of Denise are not exactly where they are being sampled by the
display enhancer after the system gets warmer.  You should be able to
fine several "sweet" spots in the full 15 turn range of the fine tuning
control where you get no pixel jitter, either cold or warmed up. 
Please try this and see if it helps your problem.

Regards,
Scott Hood

-- 
--
Scott Hood, Hardware Design Engineer (A3000 Crew),  Commodore-Amiga, Inc.
   {uunet|pyramid|rutgers}!cbmvax!hood   hood@cbmvax.cbm.commodore.com
  "The views expressed here are not necessarily those of my employer!"