🚀 go-pugleaf

  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.