114 lines
6.8 KiB
Plaintext
114 lines
6.8 KiB
Plaintext
From: movshon@acf8.UUCP (Tony Movshon)
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Newsgroups: comp.sys.ibm.pc
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Subject: Re: Upgrading an old IBM PC/XT to 640k
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Date: 2 Mar 88 02:54:00 GMT
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The following recipe for upgrading IBM PCs and XTs to 640k of memory on
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the motherboard was posted in 1985 by Mike Brown of Nicolet. I did this on
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my PC Portable (XT motherboard) and it worked like a charm. It seems like
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it's time for a repost ...
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--------------------------------------------------------------------------
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This document describes how to install 640k of RAM on the system board
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in the IBM XT and the IBM portable (which uses the same mother board).
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Parts list:
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Quantity Description
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---------------------------------------------------------------
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18 256k by 1 Dynamic RAM chips (any of the following)
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Manufacturer Part number
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----------------------------------
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Fujitsu MB81256-15
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Hitachi HM50257-15
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Mitsubishi M5M4256-15
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NEC uPD41256-15
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OKI MSM41256-15
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TI TMS4256-15
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Toshiba TMM41256-15
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1 74LS158 Decoder/multiplexer Integrated circuit
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IBM XT Instructions:
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1. Turn off the system unit, and disconnect the power cables, monitor and
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keyboard cables and any cables that may be connected to expansion boards.
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Remove the monitor and the keyboard. Place the system unit in a convenient
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work area.
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2. Take off the cover from the system unit by removing the 5 screws on the
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back (4 corners and top center), slide the cover forward and tip up to
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remove completely.
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3. Take out any boards installed in the expansion slots by removing the hold
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down screw at the rear of the chassis, and pulling the card straight up.
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4. The floppy disk drives will have to be removed to gain access to portions
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of the mother board. This is done by removing the screws on the left side
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of the drive(s). Gently slide the drive(s) out of the unit far enough
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to get at the cables plugged into the back of them. Making note of where
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each cable goes, remove the data and power cables by gently pulling them
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away from the drive. When the cable are off, remove the drive(s) from the
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chassis and set them aside.
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5. Refer to figure 1 and locate the jumper block labeled E2 on the mother
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board. It is located near the edge of the board near the power supply.
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6. A jumper has to be installed between pads 1 and 2 on E2. This can be
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done without removing the mother board using a short piece of wire. Hold
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the wire with a pair of needle nose pliers and heat up one of the pads
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with a soldering iron. When the solder melts, push the wire into the pad
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and remove the soldering iron. Do the same thing with the other end of
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the wire and pad.
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7. Refer to figure 1 and locate the IC socket labeled U84 on the mother
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board. This will be an empty socket near the front of the board,
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underneath where the floppies were mounted. Install the 74LS158 chip in
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this socket making sure pin 1 (marked with a dot or notch) is pointing
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away from the front panel.
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8. Remove the 64k RAM chips in the rows labeled BANK 0 and BANK 1 (9 in each
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bank) on the mother board using an IC puller. If you currently only have
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128k of memory on the mother board (BANK's 2 and 3 empty) you can move
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these chips to those banks. Be careful not to damage the pins when
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removing them (you can sell them to a friend whose machine has amnesia).
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9. Install the 256k RAM chips in the now empty sockets of BANK 0 and BANK 1
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making sure they are installed correctly with pin 1 pointing away from
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the front panel. You should now have 2 banks (0 and 1) of 256k RAM chips,
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and 2 banks (2 and 3) of 64k RAM chips, giving you a total of 640k.
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10. Refer to figure 1 and locate the switch block, SW1 on the mother board.
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Make sure that switch positions 3 and 4 are in the OFF position.
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11. Re-install the floppy drive(s) by sliding them into the front panel about
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half way and reconnect the data and power cables in the same locations
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they came off of. Push the drive(s) the rest of the way in and anchor
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them with the screws removed earlier.
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12. Re-install the your expansion boards (minus any memory boards that used
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to be in the system) in the reverse order of when you took them out.
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13. Put the cover back on, re-connect the cables and install your monitor and
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keyboard.
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------------------------------------------------------------------------
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| EXPANSION | |
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| SLOTS | |
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|--------------------------------------------- |
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| ------------------------------------ |
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| | BANK 0 | ---- |
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| ------------------------------------ E |12| |
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| ------------------------------------ 2 |34| |
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| | BANK 1 | --- ---- |
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| ------------------------------------ |S| |
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| ------------------------------------ |W| |
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| | BANK 2 | |1| |
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| ------------------------------------ --- |
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| ------------------------------------ |
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| | BANK 3 | --- |
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| ------------------------------------ |U| |
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| |8| |
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| |4| |
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| --- |
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------------------------------------------------------------------------
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Figure 1
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(XT/Portable motherboard)
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--------------------------------------------------------------------------
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Tony Movshon
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Internet: movshon@nyu.edu
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Usenet: movshon@cmcl2.uucp or {ihnp4|allegra}!cmcl2!xp!tony
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US Mail: Department of Psychology, NYU
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6 Washington Place, room 1083
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New York, NY 10003
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Phone: (212) 998-7880
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