hcj@lzaz.ATT.COM (HC Johnson) (07/22/89)
A while back I mentioned I had a 520 ST that had been upgraded to 1 MEG using piggy back soldering and have received several inquiries. I also requested that if anyone had an old copy of how to do this that they repost it. < SILENCE>. Let it be known that I bought this ST USED, and the upgrade was already in place. In looking at it the following is apparent. 1. all the pins, save 2 are soldered to the pin under the piggy back. 2. THERE ARE CUTS on the mother board. 3. Six (6) series resister lines go out to the drams. 3 go to the new (piggy) back ones. the othe 3 , would I think, go the the original drams. I will sketch the mess out, and post it, BUT I cannot guarantee I find all the cuts. I'm sure this was common stuff 2-3 years ago. Doesn't anyone have real documentation on it? Howard C. Johnson ATT Bell Labs att!lzaz!hcj hcj@lzaz.att.com
randyh@hpsad.HP.COM (Randy Hosler) (07/24/89)
The following is an article that was posted here some time ago.
Hope it helps.
Randy
--------
The 520ST One Meg Upgrade
=========================
by Russell Vail
WHAT IS REQUIRED
----------------
To do the upgrade, you will need: 16 256K RAM chips, 150 ns access
time, e.g. NEC 41256C-15 or TMM4256-15 which is what I used. You can
order them from MICROPROCESSORS UNLIMITED, INC.,24000 South Peoria Avenue,
Beggs, Oklahoma 74421 (918) 267-4961, or if you know of a place locally.
A good miniature soldering iron, with a small tip. Approximately
four foot of wire. If you have it, use wire-wrap wire. But you can use
ordinary thin single strand wire. De-soldering equipment. E.g. a sucker.
Normal tools, such as a screwdriver, tweezers, pliers etc.
How it's done:
--------------
1. Open up the 520ST case; pull off the keyboard connector; if there is
shielding round the circuit board, take that off, and remove the board.
2. Identify all the RAM chips
(U45,44,43,42,38,34,33,32,30,29,28,25,24,18,16).
Desolder and remove all the capacitors adjacent to them. This is to give
you more room to do the soldering of the chip pins. Using a solder
sucker, open up the holes that used to be occupied by the capacitors. Do
this step carefully to avoid damaging your ST board.
3. Take each of the new ram chips in turn. Bend pins 4 and 15 so that
they are horizontal to the package, and cut off the tips of pins 4 and 15
so that they are about half length. Place the RAM chip on top of the old
one (same way around!)with all the pins except, 4 and 15, touching the
chip underneath. Carefully solder each pin, except 4 and 15. The best
way to do this is to put the tip of the iron on both pins, heat them both
for a second(no more) and add a little solder, which should flow around
both legs. After doing each chip, check all pins with a magnifying
glass.
4. Replace all the desoldered capacitors and solder them back exactly as
they were. Please note that your should not attempt to power up your ST
until you have completely finished step 6.
5. Now for the wires. The first one connects the RAS on pin 4 of all the
new chips, to pin 18 of U15. If you are using wire-wrap wire, then strip
off five inches of insulation, Solder the end to pin 4 of the new U45.
Measure the distance to the next pin, and shift over that much insulation
before soldering. Continue until all the ships are done. Route the wire
through the hole in the PCB next to U15 and connect to pin 18 of U15.
6. The second wire connects all the pin 15's of the new U45-U32 to U15
pin 22. The third connects from pin 15 of the new U30-U16 to U15 pin 21.
7. Now sit back and think. Read through these instructions again. Have
you done everything? look at the board. Are all the joints good? If you
have a meter, check for continuity on all the wires. Applying power with
errors might destroy a lot of chips. If you are confident, then put the
board back in the case (your workbench is probably covered with bits of
wire and solder), connect it to the monitor, disk and power supply, and
switch it on.
8. If it boots, then you are probably there. If you have SID (supplied to
the developers only) or Kissed, then look at the phys-top variable($42E)
which should read $100000. If it is only $80000 then you have only 512K.
If you don't have SID, load basic and type in this program.
10 def seg=0
20 loc#=1070
30 print peek(loc#)
This should print a result of 1048576. If you get half this (524288) then
you have only 512K.
DISCLAIMER: The author of this doc file or ST Report are not responsible
for your workmanship, success or failure on this upgrade project.gert@prls.UUCP (Gert Slavenburg) (07/25/89)
Several postings have recently asked about the old upgrade of a 520ST to 1M by piggybacking 256k RAM chips. The initial upgrade description article was from me and posted on comp.sys.atari.st in August 1985. I have no copy of the original article anymore, but you can find a reproduction of it in BYTE : BYTE Feb 86, Vol 11, No 2, p. 372-376 (BIX Atari ST) The original upgrade worked for me, and still does. However, many sources have published improvements w.r.t. electrical signal quality. I believe it is a good idea to use thicker wires than I originally suggested. REMEMBER : ONLY DO THIS UPGRADE IF YOU HAVE HARDWARE EXPERIENCE AND HAVE ACCESS TO SOME HARDWARE DEBUG TOOLS IN CASE IT FAILS. Gert Slavenburg (..!pyramid!prls!gert) Disclaimer : Try this upgrade at your own risk. It will void your warranty and may affect your rights to repair or exchange.