341 lines
14 KiB
Plaintext
341 lines
14 KiB
Plaintext
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A 2.5 Meg Socketed Ram Upgrade for the 1040ST
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A Shareware File by Barry Orlando Dated: Dec. 28, 1988
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Introduction
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This shareware text file provides a procedure which details a 2.5
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megabyte on board RAM upgrade project. The method described replaces 16
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256K dynamic RAM chips with 16 one megabit dynamic RAM chips installed
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in chip sockets. Reinstallation of the ST's metal shield cover is also
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not impaired.
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The beauty of this modification is that pin compatibility is simplified
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by the use of sockets instead of directly soldering the 1 meg RAM chips
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(DRAMs) to the motherboard and by the fact that the removed bank of
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sixteen perfectly reusable 256K DRAMs can be resold by you to persons
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upgrading 520STfm computers to 1 megabyte.
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If you use this upgrade method, I recommend that you also use the same
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high quality low contact resistance sockets that I used and have listed
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below, than to use any other standard sockets. These are the type and
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quality which are used on expansion boards made for the IBM clones.
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I originally wrote this procedure to aid me in upgrading my own
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1040ST's memory to 2.5 megabytes because I didn't trust myself not
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making mistakes and possibly damaging any of the electronic components,
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especially the new DRAMs which I didn't consider cheap. I might note
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that my 1040ST's pc-board was marked Rev 4, but I don't believe that
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any other recent board revisions (if they exist) for boards with 32
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256K DRAMs installed should affect this procedure.
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Disclaimer of Liability
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I make no claim that this modification will work for you. I can
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only say that it worked for me. This modification should not be
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attempted by anyone except by someone with experience repairing or
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building digital electronic circuits. Performing this modification will
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be done at your own risk and may void the warranty on your computer.
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1
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Background
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The 256K dynamic ram chip differs from the 1 meg dynamic ram chip by
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having one additional connection, namely the address input A9. The
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following chip diagram illustrates this and shows pin layouts:
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256K 1meg
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------\__/------ ------\__/-----
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A8|1. 16|VSS Din|1. **18|VSS
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Din|2 *15|CAS WE|2 17|Dout
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WE|3 14|Dout RAS|3 *16|CAS
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RAS|4 *13|A6 NC|4 15|A9
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A0|5* *12|A3 A0|5 *14|A8
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A2|6* *11|A4 A1|6* *13|A7
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A1|7* *10|A5 A2|7* *12|A6
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VDD|8* * 9|A7 A3|8* *11|A5
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---------------- VCC|9* *10|A4
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---------------
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Truth Table for above chips:
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____________________________
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A0-A9 Address Inputs
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CAS Column Address
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Din Data In
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Dout Data Out
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RAS Row-Address Strobe
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VDD Power (+5V)
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VSS Ground
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WE Read/Write Input
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NC Not Connected
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* pc-board pin compatible
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** pc-board pin compatible on most chips
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The 2.5 megabyte modification essentially reconnects all pins as
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previously connected on the lower of two banks of RAM chips plus adds a
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new line from the previously unused A9 pin on the ST's MMU (pin 64 of
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U15) to all new 1 meg chip pins A9 via a new 33 ohm resistor. Some of
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the Address leads are interchanged, but this has no effect on the
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operation of the computer.
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Major Tools
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1. Desoldering iron (I recommend the spring loaded type that
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incorporates the head source.)
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2
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2. 15W grounded soldering iron (Radio Shack 64-2051 or similar)
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3. Wire wrap clip and stripping tool
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4. Exacto knife
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5. 3-5 power magnifying glass or jewelers eyepiece
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Parts Required
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1. One 33 ohm resistor, 1/4 watt, 5%.
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2. 5 feet length of 30 gauge wire, Kynar wire wrap solid
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conductor (Radio Shack 278-502).
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3. 16 double contact low profile dual-in-line I.C. sockets (D.C.
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Electronics catalog no. T02-18, cost: $0.12 each)
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4. Pack of 10 "Socket Wrap ID" (D.C. Electronics catalog no.
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16-ID, cost: $2.05) You can get in touch with D.C. Electronics at
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the following location:
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D.C. Electronics
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P.O. Box 3203
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Scottsdale, AZ 85257
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(800) 423-0070
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5. 16 one megabit dynamic RAM chips, 120ns (I used Hitachi Part
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no. HM511000-12, and paid $24.00 each plus state tax and $4.00
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shipping from Ed at Computronix on Dec 16, 1988). You can get in
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touch with Ed at the following location:
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Computronix
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2151 A O'Toole Ave.
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San Jose, CA 95131
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(408) 943-0771
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Work Area
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Prepare your work area by placing a towel on your flat working
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surface and cover it with a layer of aluminum wrapping foil. This
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provides padding for the components and a conductor for static
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electricity.
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Precautions
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Since the slightest static discharge could easily damage
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components on your computers pc-board, always keep one hand on the
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metal foil bonded along the outer rim of the pc-board before and during
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touching any part of the pc-board or its components. Avoid working on
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this project when the humidity is low.
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3
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Procedure
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1. After removing the pc-board from the insides of your computer,
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desolder and remove the front 16 256K chips (U33 through U45 and U16
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through U30).
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2. Using the Exacto knife, cut the following traces on the top side of
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the pc-board:
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a. Between U30's pin 1 and U61's pin 1.
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b. Between pin 14's of U33 through U45 and U16 through U30 and
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other pin 14's of U46 through U61.
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c. Between the thru-hole (nearest to pin 1 in center of U32) of
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U32 and U46's pin 1. (Note: This thru-hole traces to U32's pin 1
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on the underside of the board.)
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3. Using the Exacto knife, cut the following traces on the bottom side
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of the pc-board:
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a. Between U30's pin 1 and the 32 ohm resistor R76.
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b. Between U32's pins 2 and 14. Do the same for U33 through U45
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and U16 through U30.
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c. Between U30's pin 4 and U15's pin 8. (Note: Cut the trace after
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it goes through the board to the bottom side near resistor R91,
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but before it reappears on the top of the board via another
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thru-hole.
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d. Between U32's pin 14 and the thru-hole located between U32 and
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U33.
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4. Preparing New Sockets and Soldering Them Inplace
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a. On all 16 new sockets, remove the internals of pin 4.
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b. On all 16 new sockets, bend all pins 1 and 17 flat against
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their bottom then up against their outer side.
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c. On 14 of the new sockets, bend pin 18's flat against their
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bottom and pointing straight out to the side.
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d. On the remaining two, bend both pin 18's flat against their
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bottom but back and down so it will just reach and fit into the
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pc-board hole of it's adjacent pin (pin 17). These two sockets
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will be installed and soldered with the socket's pin 18 going into
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the old 256K chip's pin 16 hole below the new socket's pin 17.
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Trial fit these two sockets at this time.
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e. Using a pair of scissors, cut pieces of "Socket Wrap-ID"
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plastic markers for sandwiching them between the new sockets and
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the pc-board during installation. These little plastic markers
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should be cut so as to electrically isolate the socket's pins 1
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and 17 from leads and traces on the pc-board, and from pin 18 of
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the socket for the two separately prepared sockets above, but also
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so as not to interfere with seating the socket's four pads flush
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with the top of the pc-board upon installation.
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f. Solder the two sockets with the bent back pin 18 and markers
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4
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into U30 and U33.
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g. Solder the remaining sockets with markers into U34 through U45
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and U16 through U29. Pin 18 of these socket's must be soldered to
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the top of the board at the nearest thru-hole that the pin 18 just
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barely reaches. Use plenty of heat as these thru-holes are big
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heat sinks.
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5. Mounting The New 33 Ohm Resistor
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a. Install a new 33 ohm resistor on the pc-board by drilling two
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small holes from the top at points near capacitor C55 and resistor
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R70. Make sure you don't drill through a trace on the other side
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by holding the pc-board up to a bright light and marking the spots
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with a pencil.
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6. Wiring
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Wire the following connections on the top side of the board:
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a. Between U32's new socket's pins 1 and 17 and a thru-hole on the
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pc-board between U32 and U33. This thru hole is the only one that
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has a trace that run to another thru-hole between U46 and U47 on
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the top side of the board.
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b. Between U16's new socket's pins 1 and 17, and pin 2 of U54.
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Solder the wire directly to the side of the chips pin 2.
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c. Between each of the remaining new socket's pin 1 and 17 and a
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thru-hole in back of each 256K RAM chip (i.e., U47 through U53 and
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U55 through U61). These thru-holes are the ones that you will find
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traces back to either pin 2 or pin 14 of U47 through U61 and then
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trace over toward U22, U23, U26, and U27. Actually, pins 2 and 14
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are tied together on the bottom of the board for every 256K RAM
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chip still installed. So that's 14 more wires altogether (i.e.,
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each new RAM chip's pins 1 and 17 will be connected to the pins 2
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and 14 of the 256K chip directly in back of it.
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Wire the following connections on the bottom side of the board
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(Note: all pin numbers here refer to the pin numbers on the
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pc-board, not the pin numbers of the new sockets or new ram
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chips):
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d. Between U15's pin 64 and one side of the new 33 ohm resistor.
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e. Between all pin 14's of U32 through U45 and U16 through U30,
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and the other side of the new 33 ohm resistor.
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f. Between all pin 2's of U32 through U45 and U16 through U30, and
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the thru-hole near R91 which had its trace cut to U30's pin 4.
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This thru-hole traces back on top of the pc-board under the bank
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of resistors and over to U15.
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g. Between U61's pin 1, U30's pin 4, and the cut trace side of
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resistor R76.
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h. Between U30's pin 1 and U61's pin 3.
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8. Inspect all solder joints with the magnifier for solder shorts and
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5
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faulty connections. Verify that all connections were made correct.
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9. Install the new 1 meg RAM chips into their new sockets.
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10.That's it! Clean isn't it? Now sit back and admire your work.
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12.Reassemble the computer and reconnect the monitor and power cord and
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let it whirl!
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Shareware Policy
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I am distributing this documentation as a $15.00 Shareware File.
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Please feel free to re-post on your favorite Information Service or
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local BBS. I ask only that you do so in its original unaltered form.
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If you have followed these instructions and everything worked for you,
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I'm sure you will appreciate the effort I put into documenting this
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project and the money it has saved you from buying one of those
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expansion boards on the market or by the time you could have spent
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trying to figure such a project out by yourself. Please send your
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shareware user registration fee to:
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Barry Orlando
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1120 Deerfield Dr.
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Napa, Ca 94558
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All registered users will be sent a free utility disk which includes a
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program to test the new RAM as well as instructions on how to further
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modify the computer to a full 4 megabytes.
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Good Luck!
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6
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