Z4648252@SFAUSTIN.BITNET (Z4648252) (08/03/89)
NOTE: This is an REVISED,TESTED version of the original text
downloaded from CompuServe. December 6, 1985
(This was REVISED AND TESTED by an annonymous engineer on
Atari's developement staff. The addition of the resistors
should provide a long life to your machine, but the warning
below is STILL IN EFFECT. This is not an official sanction
of the modification. USE WITH CARE!!!)
Here's the 1 Meg upgrade directions:
THE FOLLOWING ONE MEG DOCS ARE ANCIENT AND WERE FOUND ON VARIOUS
BBSes. I USED THIS TO UP MY 520, WHICH STILL WORKS FINE IN SPITE
OF ITS JEALOUSY IN THAT I NOW HAVE A MEGA2. FOLLOW DIRECTIONS
AT YOUR OWN RISK IS ALL THAT I CAN SAY. IT WORKS FOR ME!
Larry Rymal <Z4648252@SFAUSTIN.BITNET>
From: gert@pescadero
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 ns access time type, e. g. NEC
41256C-15 (avilable at e. g. Fry's Electronics, Sunnyvale,
CA for $2.77 each)
A good quality, preferrably temperature controlled soldering
iron, with a minature 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 #24 AWG insulated wire and a good
stripper for it and 2 feet of #22 AWG solid tinned copper
bus wire. You will have to route 3 wires over a sequence if
I.C. pins.
Desoldering wick and solder suction tool.
Philips type screwdriver (for opening your ST), tweezers,
pliers, etc.
A steady hand and self-confidence.
Explaination of the modification :
(Please read the rest of this document before starting. It
may save you time and an 520ST)
The current memory inside the 530ST 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 chis
foring 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, such
that 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, 28,
27, 26. Note that all chips are adjacent, though the
numbering has gaps. RAS0, CAS0H, and CAS0L are supplied from
U1 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 pins. Thus they will end up sharing
addresses, data, WriteEnable and power and ground with the
existing chips.
All RAS pis 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-2119C 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 off 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 of the capacitors adjacent to the
existing RAM chips. (DO NOT SKIP THIS STEP. You'll lose time
if you do, and worse, the modification will no be reliable
since you can't solder 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 or each capacitor, turn
over to the component side and heat the islands wile pulling
the capacitor out with the tweezers.
Step 3: Open up the holes of all the desoldered capacitors,
using a combiation 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 & 3 are the only ones that may damage your ST
PC board. Be sure not to use excessive force while pullling
out the capacitors. If you damage your PC board 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 oes. 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
hey are perpendicular to the package (instead of having
slightly spread "cowboy legs"). Use pliers to bend pin 4 and
15 such that the legs are 180 degrees from their normal
position, so they stick up in the air above the plane of the
top surface of the chips. Don't make an absolute sharp 180
degree bend since some manufacturers' pins may snap off.
Leave a little curve in the leg, but insure that is above
the plane of the top surface of the chip.
Using #22 AWG to #16 AWG tinned solid copper wire you will
form three buses along the top surface of the new d-rams.
Cut a #22 AWG solid copper wire the length of the 16 d-rams
on the PCB. The RAS bus is formed by soldering all the pin
4's of the new d-rams to the solid copper wire. The bus wire
must be seated against the top surface of the new d-rams
without a gap. This insures clearance between the top shield
and the pins of the d-rams.
After soldering all 16 d-rams to the bus clip off any
portion of the pins that extend above the top of the bus
wire. Now cut a #22 AWG solid copper wire the length of the
16 d-rams. Place the bus wire along the top surface of the
new d-rams in contact with all the pin 15's of the new
d-rams. Solder every pin 15 to this bus and as above insure
that the wire is seated solidly against the top surface of
the new d-rams. Cut off all excess pin length sticking up
above the top of the bus wire. Using diagonal cutters remove
the section of the bus connecting the new U30 pin 15 to the
new U32 pin 15. This divides the bus in half with the new
U16, 17, 18, 24, 28, 29 having a common pin 15. The new U32,
33, 34, 38, 42, 43, 44, 45 now have a common pin 15,
seperated from the other common bus.
(NOTE: until step 6 is finished, do no in any way apply
power to your ST. This intermediate state of affairs will
damage your memory chips!!)
Step 5: Remount all the desoldered capacitors. Bend the pins
like they were before resoldering, suchthat they will not
touch the lower shielding. Solder from the non component
side.
Step 6: Orient the 520ST PCB so that you are looking at the
solder side of the PCB (non-component side), with the row of
d-rams nearest you. Find the double square pattern of pads
at the 68-pin socket of the memory controller, U15 (3H2119).
The following is a guide to locating the six memory
controller pins necessary to complete the wiring. The socket
is numbered conterclockwise, starting with pin 1, the square
pad (look closely) in the middle of the bottom outside row.
The sequence, moving counterclockwise from pin 1, first on
the outside square ONLY: (NOTE: the sequence ")(" means to
make a 90-degree turn counterclockwise, i.e. around the
corner)
1,3,5,7,9)(10,12,14,16,18,20,22,24,26)(27,29,31,33,35,37,39,
41,43)(44,46,48,50,52,54,56,58,60)(61,63,65,67
The sequence, moving counterclockwise along the inside
square only, and starting with the left side of the bottom
row:
(62,64,66,68,2,4,6,8)(11,13,15,17,19,21,23,25)(28,30,32,34,3
6,38,40,42)(45,47,49,51,53,55,57,59)
Six 68-ohm 1/4W plus/minus 10% carbon film resistors must be
added when adding memory. These series terminating resistors
minimize undershoot which may damage BOTH BANKS of d-rams if
omitted. Solder a 68-ohm resistor to pin 18 of U15, RAS1.
Solder a #24 AWG stranded wire from the remaining end of the
68-ohm resistor to the pin 4 bus (RAS) of all the new
d-rams. that is the new U16, 17, 18, 24, 25, 28, 29, 30, 32,
33, 34, 38, 42, 43, 44, and 45.
Solder a 68-ohm resistor to pin 22 of U15, CASH1. Solder a
#24 AWG stranded wire from the remaining end of the 68-ohm
resistor to pin 15 bus (CAS) of the new
U45,44,43,42,38,34,33,32.
Solder a 68-ohm resistor to pin 21 of U15, CASIL. Solder a
#24 AWG stranded wire from the remaining end of the 68-ohm
resistor to pin 15 bus (CAS) of the new U30,
29,28,25,24,18,17,16.
For best results in all three cases above solder the wires
coming from the resistors to the middle of the three bus
wires in a "T" fashion rather than at one end of the buses.
Use a continuity tester to find the following three traces
-- do not depend on visual inspection. Now install three
68-ohm series terminating resistors in the original 512K
bank of ram. Be very careful while soldering to these narrow
traces, since excessive heat can easily lift a trace from
the board. Use an Exacto knife to gently remove solder mask
from traces.
Cut the trace leading from pin 8, RAS0, of U15 near U15.
Solder a 68-ohm resistor in series with the trace.
Cut the trace leading from pin 6, CAS0H, of U15 near U15.
Solder a 68-ohm resistor in series with the trace.
Cut the trace leading from pin 7, CAS0L, of U15 near U15.
Solder a 68-ohm resistor in series with the trace.
Step 7: Sit back. Use Brain. Do you feel confident about the
quality of your work? No mistakes? Check evrything once
again if you are but a little uncertain. Applying power with
errors might make your ST into a decorative, nonfunctional
piece of art. OK. Either rebuild your ST into its shielding
and cabinet, or put it onto a surface clear of wires and
solder remians and connect it to monitor, disk and supply.
Boot it.
It 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 developer 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 developer 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 Meg hex).
If bit errors occur, the ST bootROM did not detect the
extension (it checks all bits of 512 locations by testing a
psedo random sequence, before accepting a memory bank). Try
to pin point 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 the RAM pins. May also be
that you have a flaky new pin connection.
That's all there is...
PLEASE REMEMBER THAT I HAVE NOT TRIED THIS AND I AM SIMPLY
PASSING THIS ALONG FOR THOSE WHO WOULD LIKE TO TRY DOING
THIS.
--Dwight McKay (75776,1521)
Larry Rymal in East Texas <Z4648252@SFAUSTIN.BITNET>