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#53 2 20 Jul 86 17:49:12
From: David James
To: All
Subj: Upgrade IBM Memory Sidecar to 512K
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
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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
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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).
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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)
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