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Altering the IBM PCjr 128 Memory Module to 512K

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                ALTERING THE IBM PCJR 128 MEMORY MODULE

                              TO 512K


              The following instructions will show you how to alter
         your IBM PCJR side mounted 128k memory module to 512k. this
         of course will give a potent 640k machine providing you have
         the later release of the 128k and not the 64k original.

              You must be able to use a soldering iron and be able to
         de-solder connections. I am not an expert with a soldering
         iron but I found just being careful and taking my time I was
         able to complete the operation in about four hours without
         damaging my board or components as I have heard others have
         done.

              An important factor in my wanting to make this
         alteration was the obvious cost. total parts cost for me was

         approx. $70.00. I understand that the parts may be purchased
         cheaper elsewhere so you may want to shop around. If you have
         been hungry for more memory in your JR and saw the prices for
         commercial memory expansions you can see that you will save
         up to $400.00 by doing this operation.



                                  STEPS


         1. REMOVE THE 128K MEMORY BOARD FROM THE MODULE. HOLD THE
         COMPONENT SIDE TOWARDS YOU AND LOOK FOR 16 CHIPS MOUNTED IN A
         ROW VERTICALLY ALONG ONE OF THE LONG EDGES OF THE BOARD.
         THESE CHIPS WILL ALSO HAVE THE SAME NUMBER ON THEM. THESE ARE
         THE 16 CHIPS YOU WILL REMOVE.

         2. CAREFULLY UNSOLDER AND REMOVE THESE CHIPS. BE VERY CAREFUL
         NOT TO ALLOW SOLDER TO GET ON OTHER COMPONENTS, IF IT DOES,
         REMOVE IT. ALSO BE CAREFUL ABOUT SCRATCHING THE BOARD AS YOU
         MAY DISCONNECT A PRINTED CIRCUT FROM A COMPONENT.

         3. NOW BEFORE YOU REPLACE THE CHIPS YOU JUST REMOVED I HIGHLY
         RECOMMEND YOU INSTALL 16 PIN SOCKETS WHERE YOU JUST REMOVED
         EACH CHIP FROM. THESE SOCKETS ARE VERY INEXPENSIVE AND WILL
         ALLOW YOU TO PLACE THE NEW LARGER CAPACITY CHIPS ON THE BOARD
         WITHOUT EXPOSING THEM TO THE HEAT OF THE SOLDERING IRON.

         4. BEFORE GOING ANY FURTHER YOU HAVE TO ALTER A JUMPER ON THE

         BOARD SO IT WILL OPERATE WITH THE NEW 256K CHIPS. LOOK IN THE
         APPROXIMATE CENTER OF THE CIRCUT BOARD FOR A SMALL RECTANGLE
         OUTLINED WITH WHITE PAINT. IN THE CENTER OF IT ARE THREE
         SOLDER POINTS.



                        EXAMPLE


                          _______________
                         |               |
                         |  O----O    O  |
                         |_______________|



         5. YOU WILL NOTICE THAT THE TWO LEFT HOLES ARE CONNECTED BY A
         JUMPER. THIS SETUP IS SELECTING THE BOARD FOR 64K CHIPS.
         BECAUSE YOU ARE INSTALLING 256K CHIPS YOU HAVE TO JUMP THE
         TWO RIGHT MOST HOLES. CUT THE WIRE LEADING TO THE TWO LEFT
         MOST HOLES AND INSTALL A JUMPER ON THE TWO RIGHT HOLES
         (SOLDER).


         6.PLUG IN YOUR NEW LARGER (MEMORY) CHIPS INTO THE SOCKETS YOU
         HAVE PREVIOUSLY INSTALLED. THE RECOMMENDED CHIPS ARE:
                   256Kx1 DRAMS 150ns
         USE CAUTION WHEN PLUGGING IN YOUR NEW CHIPS SO AS NOT TO BEND
         ANY PINS. I ACCIDENTALLY DID THIS WITH JUST ONE PIN FROM ONE
         CHIP AND THE BOARD FAILED TO FUNCTION. BY RECHECKING MY WORK
         I SAW THAT A LEAD FROM A CHIP BENT UNDERNEATH THE CHIP AND
         FAILED TO GO INTO THE PLUG SOCKET.

         7. NOW GO TO THE ADDRESS SWITCHES TO THE END OF THE CIRCUT
         BOARD. THIS IS THE SMALL BOX WITH FOUR SMALL SWITCHES THAT IS
         VISIBLE TO THE REAR OF THE MODULE. TURN ALL OF THESE SWITCHES
         ON. THIS ALLOW YOUR BOARD TO ANSWER UP AS 512K. REPLACE THE
         CIRCUT BOARD INTO THE MODULE AND PLUG IT IN.
 * Origin: LITTLE BLUE Grand Rapids, Mi. (616) 243-2645 (120/28)

See Also