🚀 go-pugleaf

In article <71542@cup.portal.com> Bob_BobR_Retelle@cup.portal.com writes:
>Stephen Matson asked about expanding the memory in a 520STFM..
> 
>The first step is to unsolder all 320 holes that Atari conveniently
>soldered shut for you..

This is by far the most time consuming part of the operation.  BTW, the
holes are soldered shut as a result of wave soldering the boards, not by
any deviousness on the part of Atari.  I found the purchase of a
desoldering iron from Radio Shack to be a great help here, as I'm a
total spaz with a solding iron and a separate solder sucker.

>Then, for safety's sake, install sockets in all RAM locations.
>
>The bypass capacitors aren't particularly critical.. use small
>form factor .01 mfd units to make them fit..
>
>The RAM chips are 256K x 1, 150 ns units.  You can install faster chips
>if can get them cheaper..
> 
>The last step is to install three resistors in the RAS and CAS lines
>from the MMU chip to the new RAM bank.  I forget the exact values of
>these resistors (don't have a 520STFM myself), but they're in the range
>of 150 ohms.  There should already be three resistors going to the
>existing bank of RAM.. check to see what these resistors are, and
>emulate them in the new installation.

I seem to recall the values being smaller, but it might be different for
a Mega ST.

>That should be it.. the operating system will recognize the new RAM
>automatically.. you don't have to do anything special to get it to
>see the full 1 Meg of memory..

Bob summed it up rather well, although I'd like to caution you on ESD
(electrostatic discharge).  You can easily fry your RAM chips or other
IC chips with a discharge you can hardly feel.  A grounded wrist strap
is a good idea, as is using some anti-static spray around your work
area.  Try to resist the temptation to scuff your socks on the carpet or
rub the cat before you pick up the board!

Good luck!
**********************************************************************
Jonathan Whitcomb                    UUCP:  whitcomb%aurgate@mcnc.org
Alcatel Network Systems              
Raleigh, North Carolina              GEnie: J.WHITCOMB3