Here are the TOS ROM upgrade instructions which I received from ATARI
along with my ROMS.  I have attempted to reproduce the essential
features of the one important Figure in the instructions.  Please note
that I have not verified the "BOOT EPROM Version" instructions, since I
had the more common "MASKED BOOT ROM Version" which simply required
replacing the two old ROMS with six new ones.

I have had the ROMS installed for about two weeks now, and have
encountered no real problems (I have a 1 meg ST with the "six
resistors").  The only programs which I have found that don't work
properly are the PD ramdisk and fontloader programs (but M-disk works
fine).  TOS can still be loaded from disk if desired.

					Good Luck!
					R. Brad Kummer
					AT&T Bell Labs	Atlanta, GA

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			TOS ROM UPGRADE

Once plastic and shield have been removed, locate the ROM socket area of
the board (left side, near cartridge slot).  There are three versions of
the 520ST that have been produced to date; the ROM installation will
vary according to the version of the board you have, so identify your
board from the descriptions below:

MASKED BOOT ROM Version == This is the most common and is the easiest to
upgrade.  You have this version if no jumper wire is visible along the
ROM socket area and the two ROM chips don't have labels on them.  To
upgrade, simply remove the two existing chips by wedging a small
flathead screwdriver between the chip and the socket and carefully
lifting up on the chips.  Once the two old chips have been removed,
insert the six new ROMs as shown in the figure below.  Please note that
it is extremely important that each ROM be put in with pin 1 on the top
right corner of the chips as shown in the figure.

BOOT EPROMS Versions 1&2 == These are very early computers which were
produced before masked ROMS were available.  You have this version if a
jumper wire is visible running from below the socket marked U7 to the
middle front of the socket marked U3 and/or the two chips in the sockets
have labels with handwritten markings on them.  To upgrade these
versions requires soldering and desoldering, so if you don't feel
comfortable with a soldering iron, it is strongly recommended that the
upgrade be done at an authorized Atari Service Center.  The first thing
you will need to do, if you decide to do the upgrade yourself, is remove
the PC board from its bottom plastic cover.  Now turn the board upside
down and look at the area underneath the ROM sockets marked U4,U5,U6,U7.
Looking at pins 27 and 28 on these sockets you should be able to see a
solder bridge shorting the two pins together; this short needs to be
desoldered on all four sockets.  Next, turn the board rightside up again
and look between U3 & U4, U4 & U5, and U6 & U7; toward the right hand
side between each of these sockets should be a cut trace.  This trace
normally connected all the pin 27's together, so you will need to jumper
it back the way it was before it was cut.  The easiest way is with
three jumpers; first jumper pin 27 of U3 to pin 27 of U4; second, jumper
pin 27 of U4 to pin 27 of U5; and third, jumper pin 27 of U6 to pin 27
of U7.  Before finally plugging in the new ROMs, verify your work by
checking for continuity between pin 27 of the sockets and A15, which can
be found on pin 43 of the 68000 CPU chip (U10).  Also make sure that all
pin 27's are disconnected from all pin 28's.

---------------------------- Figure ---------------------------------
        _____________________________________________________
    +---|
    |   |-
    |   |-  Cartridge
    |   |-    Slot
    |   |-
    |   |-
    +---+
       |
  ------   +-----------+ <== PIN 1
  |    U2  |  C026160 <|     +-----------------------+
  |        +-----------+     |          CPU          |
  |        +-----------+     |_______________________|
  |    U3  |  C026161 <|
  |        +-----------+
  |        +-----------+
  |    U4  |  C026162 <| <== NOTCH
  |        +-----------+
  |        +-----------+
  |    U5  |  C026163 <|	NOTE: Be sure to orient ROMS with notch
  |        +-----------+		as shown.  Lettering on ROM may
  |        +-----------+		be inverted.
  |    U6  |  C026164 <|
  |        +-----------+
  |        +-----------+
  |    U7  |  C026165 <|
  |        +-----------+
  |      ======= =======
  |_________________________________________


-------------------------------------------------------------------------------

Here is an addendum to installation of the ROM after following the above
instructions.

  Installation is generally no problem. The worst part of the
  procedure is unsoldering the metal shield from the PC board.
  There are six ROM's to install in positions U2 to U7. Only
  U4 and U7 were silk-screened on the board, but U2 is the "top
  most" (nearest to rear) socket. A screwdriver is handy for
  prying out the old devices. The ROM's aligned quite well and
  no pins were bent out of place. In case you didn't notice in
  your haste, the indexing groove on the old chips were on the
  right hand side!

  Remember to observe good anti-static, defensive practice when
  handling the parts. Just to be safe, handle the old ROM's
  carefully in case you blow up one of the new ones and need to
  re-install.

  Overall dexterity/skill level: A little more skill than a
  Heathkit one nighter is required, but not much. Hardware
  novices should be able to do the installation themselves
  without being ripped off by a dealer.
