ravi@eneevax.UUCP (Ravi Kulkarni) (09/10/85)
I am forwarding these instructions to the net as the original
author does not have access to usenet. So far he and I as far as
I know are the only ones who have upgraded to 1 meg. If you are
brave enough to try this upgrade you might want to let us know
if you succeeded or perish the thought failed.
-ravi
================================================================
Date: Wed, 28 Aug 85 20:53:05 pdt
From: Gert Slavenburg <gert@Pescadero>
Subject: manual to 520ST 1 Meg upgrade
To: info-st@eneevax
Status: RO
I had enough requests to justify sending this out to all of you at info-st.
Good luck with the modification. Cheers will be appreciated, as well as
examples of use of the full 1 Meg - it's lonely at the top.
Directions for expanding the Atari 520ST memory to 1 MByte
==========================================================
WARNING : This is a hardware modification that will void the warranty of
your 520ST. If you do not have the appropriate tools or experience you
have a substantial chance of ruining your 520ST. Proceed at your own risk !
This modification has been in my 520ST without any problems for 6 days now.
However, I have (of course) not checked with knowledgable sources at Atari
to verify if this modification endangers the long term machine reliability
and/or software compatibility (I suspect it may endanger their software
compatibility if enough of us do it !).
tools/components needed :
=========================
16 256k * 1 RAM chips, 150 nSec. access time type, e.g. NEC 41256C-15.
(available at e.g. Fry's Electronics, Sunnyvale, CA for $ 2.77 each)
A good quality, preferrably temperature controlled soldering iron, with
a miniature tip (tip should be narrow enough to avoid touching 2 I.C. pins
at the same time). E.g. Weller type soldering station.
Good quality resin core solder (thin).
Approximately 4 foot of wire-wrap wire and a good stripper for it.
(you will have to route 3 wire's over a sequence of I.C. pins. The
easiest way to do this is to have a stripper allowing you to shift the
isolation forward over the wire, solder the next point, measure new length,
shift over insulation etc. until the endpoint). The "No Nik" .014" (dark
green handle) wire wrap stripper is the best tool for this. Available
e.g. at Jensen tools, Phoenix, AZ (602) 968-6231 catalog no H4B305.
De-soldering wick and solder suction tool.
Philips type screwdriver (for opening your ST), tweezers, pliers etc.
A steady hand and self-confidence.
explanation of the modification :
=================================
(Please read the rest of this document before starting. It may save you
time and a 520ST)
The current memory inside the 520ST consists of 16 256k*1 RAM chips.
Address (A0..A8) lines are common to all those chips.
The WriteEnable line is also common to all chips.
Data (in and out) lines are (of course) individual. The RAS (Row-Address
Strobe) line is common to all chips. The 8 chips forming the high order byte
group have one common CAS line, and the 8 forming the low order byte group
have one common CAS line (CAS is used as enable for write operations,
suchthat WriteEnable can be common to both groups).
The high order group from MSB to LSB consists of U45,44,43,42,38,34,33,32.
The low order group of U30,29,28,25,24,18,17,16. Note that all chips are
adjacent, though the numbering has gaps. RAS0, CAS0H and CAS0L are supplied
from U15 pin 8,6 and 7 respectively. (The 0 indicates bank 0)
Bank 1 that you are going to build in will be "piggy-backed" on
top of the current chips, where all pins of the new chips EXCEPT RAS (pin 4)
and CAS (pin 15) are soldered to the old chips equivalent pin. Thus they will
end up sharing addresses, data, WriteEnable and power and ground with the
existing chips.
All RAS pins of the new chips are wired together and will be supplied with
the "RAS1" signal generated on pin 18 of U15 (the Memory Controller, marked
3H-2119CC or so).
The CAS pins of the 8 new high order byte chips (on top of U45..U32)
are wired together and supplied from the "CAS1H" signal generated on
pin 22 of U15.
Analogously, the CAS pins of the new U30 to U16 are wired together and
supplied with "CAS1L" from pin 21 of U15.
how to go about it :
====================
step 1 : Open up your 520ST, pull of the keyboard connector, and remove
the main circuit card from its top and bottom shielding.
Make sure to remember which screws go where and note the
keyboard connector orientation.
step 2 : Desolder all the capacitors adjacent to the existing RAM chips.
(DO NOT SKIP THIS STEP. You'll loose time if you do, and worse,
the modification will not be reliable since you can't solder
the pins obstructed by the capacitors reliably (if at all)).
To desolder them, I found it easiest to heat the island on the
non component side, and bend the wires straight. After doing that
for each capacitor, turn over to the component side and heat the
islands while pulling the capacitor out with tweezers.
step 3 : Open up the holes of all the desoldered capacitors, using a
combination of de-soldering wick and suction tool. Do this from
the non-component side. If certain holes are difficult to open
up, you may want to use a wood splinter. (push it through while
heating). Be carefull to remove all solder debris !
THE REASON for opening the holes NOW is that they will be less
accessible once you've done the other steps ! Patience is a virtue.
(NOTE : Step 2 and 3 are the only ones that may damage your ST PCboard.
Be sure not to use excessive force while pulling out the capacitors. If
you damage your PCboard anyway, cure the problem now and not later).
step 4 : In this step we will piggyback the new RAM's on top of the old ones.
Be sure to connect all pins except pin 4 (RAS) and 15 (CAS).
The best way to go about this is to do chip by chip. First bend
the pins of the new RAM's suchthat they are perpendicular to the
package (instead of having slightly spread "cowboy legs"). Use
pliers to bend pin 4 and 15 suchthat it comes out of the I.C. package
horizontal, and cut of the excess length of pins 4 and 15 (I mean
part of the pin, you still need to be able to solder to it!). Make
sure that the new RAM fits snugly on top of the old one (in the
same orientation !!!!), without intervening space and with the new
pins touching the old ones. Now solder
each pin (except the non-touching 4 and 15) to the other RAM's.
The best way to do this with least chance of damage is to touch
both the new RAM's pin and the old RAM's pin. Heat them both for
a second and add A LITTLE solder then. Wait till the solder flows.
After each IC, check all pins carefully to assure a good connection.
(use a magnifying glass)
NOTE : This step is crucial for the long term reliability of the
memory extension. A badly soldered joint may show up later as
sporadic memory errors. TAKE YOUR TIME.
(NOTE : until step 6 is finished, do not in any way apply power to your ST.
This intermediate state of affairs will damage your memory chips !)
step 5 : Re- mount all the desoldered capacitors. Bend the pins like they
were before re-soldering, suchthat they will not touch the lower
shielding. Solder from the non-component side.
step 6 : In this step you will route the 3 wires mentioned earlier. The
first wire connects pin 4 (RAS) of all new RAM's to pin 18 of U15.
The second wire connects pin 15(CAS) of the new U45 to U32 to pin
22 (CAS1H) of U15. The third wire connects pin 15 (CAS) of the
new U30 to U16 to pin 21 of U15.
The best way to do this is to use the stripper to remove 5 inches
of isolation. Solder the first IC pin to the end of the blank wire,
measure the distance to the next pin in sequence and shift over
that amount of isolation. Continue in this fashion untill all pins
in the sequence are done.
Work from U45 to the left, soldering directly to the leftover pins
on the new chips. Make sure that no wire or solder sticks out
above the top plane of the new chips, since they will almost
touch the top shielding !
Route the wires through the PC board hole below and to the left
of U15 to connect to U15 on the non-component side.
step 7 : Sit back. Use brain. Do you feel confident about the quality of
your work ? No mistakes ? Check everything once again if you are
but a little uncertain. Applying power with errors might make your
ST into a decorative, non-functional piece of art.
OK. Either rebuild your ST into its shielding and cabinet, or put
it onto a surface clear of wires and solder-remains and connect it
to monitor, disk and supply. Boot it.
If it boots, you're probably there. Test if the new memory works
by looking at the phystop variable ($42E) with SID if you have the
developper stuff. It should read $100000 (1M hex). Also note that
memcntlr ($424) now holds 5 instead of 4, and that v_bas_ad ($44E)
now holds $F80000 (screen bitmap origin).
If you don't have the developper stuff, try a single drive copy and
check that you get the whole disk in one buffer instead of two.
If the new memory does not seem to exist, use SID to deposit and
retrieve words on locations $80000 and up (1/2 M hex). If bit errors
occur, the ST bootROM did not detect the extension (it checks all
bits of 512 locations by testing a pseudo random sequence, before
accepting a memory bank). Try to pinpoint the faulty chip(s) and
remove the error.
If it doesn't boot, you're in trouble. I'm sorry. It is difficult
to give hints on what to do here. So many possibilities.
Desoldering the new chips probably won't work (if the old ones
were functional, the ST would still boot). Check for hidden
short-circuit on RAM pins. May also be that you have a flaky
new pin connection.
Good luck. I feel bad. Well, I might be able to help you a little,
call me when you're really stuck ! Evenings at (415) 965-7696.
Not after september - I'll be out of USA by then.
PLEASE :
========
Let me know if you did the modification and failed or succeeded. I'd like
to know how many people benefit from this and if it's safe enough for large
scale application. Mail to arpanet address gert@su-pescadero.
====================================================================
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