larserio@IFI.UIO.NO (LarsErikOsterud) (06/18/91)
The last weeks several people having the same trouble with their
new MEGA STE has asked me how we fixed mine, and I hope this file
can help you fix it. It's really the best machine Atari has made
so it would be terrible not to have it in perfect condition :-)
Errors on DMA-sound and video on MEGA STE - HOW WE FIXED IT !
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Here's a summary of what we found at service in Norway.
First - the errors on both machines we discovered were:
- Static/noise on DMA sound and MIXed standard ST sound.
- Sync-problems when using Spectrum512 pictures (vertical bars).
- Vertical flickering bars on monochrome (most at 8 MHz).
- Right edge of monochrome screen "flips" over to left edge
when changing screen adress/resolution in mono-mode.
We tried to find a chip that could be the cause of all these
problems and found a big VLSI chip partly hidden under the right
edge of the VME-card holder. It's chip U502 on my MEGA STE and
is called GSTSHIFTER on the print-layout. After looking at the
print-layout on both MEGA STE and standard STE we found the same
chip on standard STE, a combined sound/video chip but with a totally
different part-number. Anyway, we removed the original MEGA STE
chip (made in 1990) and replaced in with the STE chip (from 1989)
and all the problems were gone. If you want to "steal" a chip from
a standard STE it's chip U401 inside the STE (still GSTSHIFTER).
Disclaimer: Even though this solved the problems for us it might not
work for all MEGA STE's and you do this at your own risk
(I still would like Atari Corp to give some official information on
this. It's not "ONLY YOUR MACHINE" anymore. It's quite a few...)
Lars-Erik / ABK-BBS +47 2132659 / ____ ______ ________________________
Osterud / larserio@ifi.uio.no / /___ / The norwegian ST
__________/ ______________________/ ____/ / Klubben, user association