Most of the components on the SCRAM 2000 are readily sourced - the parts
list specifies a JDR Microdevices catalogue number where possible, however a
couple of parts may need a bit of explanation.



MINI TOGGLE SWITCH

    I can't find a part number for this, but it is a right angle PCB
    mount unit .2" wide, .4" high and about .5" long. If you want, you
    could just put jumper pins in and option for AutoBoot.

ZIP SOCKETS

    Yes, there is a low cost plastic 20 pin ZIP socket (out of Taiwan),
    but no, I can't tell you where to get it. Try some major socket
    suppliers. If you have no joy then just get machine pin strips and
    break them and solder them in place. Masking tape is useful to hold
    these strips while you tack them in place.

DB25 SCSI SOCKET

    This RA DB25 should be easy to source, but make sure you get the
    SHORT style. There are three lengths available, but only the short
    one will do.

SCSI TERMINATORS

    These SIP resistor paks are 8 pin 220/330 ohm nets commonned at either
    end. Not as common as other resistor paks, but fairly easy to get.

SCSI CHIP

    The DP8490V is a National Semiconductor part. It is an enhanced
    version of the venerable NCR 53C80 SCSI Controller - which lives in
    just about every Macintosh and most Amiga SCSI boards. It is pin
    compatible with the 53C80 and with apropriate driver software could
    be replaced by the 53C80. Any supplier who stocks NS components
    should be able to supply the DP8490V. For data, see NS MASS STORAGE
    HANDBOOK.

    The 53C94 is an NCR component, and I believe the is a second source
    - I can't say for sure. The 53C94 is used in a lot of designs, so
    you should be able to track it down by contacting NCR.

DRAMS

    The SCRAM 500 (in fact all my designs) uses ZIP DRAMS. The ZIP
    package is a SIP with Zig-Zag pins. The A3000 uses ZIPs. The reason
    for ZIPs is their compactness - 8Meg in an area 1" x 3.25"! The
    other reason for using ZIPs is they give you a wide range of
    configurations. You can use either 256Kx4 (1Meg chips) or 1Mx4 (4Meg
    chips). Thus you can have 2Megs with 1M chips  - or 2Meg, 4Meg, 8Meg
    by using 4M chips. Here is a list of suitable 4Meg devices:-

        MICRON          MT4C4001Z-80    1Mx4

        TOSHIBA         TC514400Z-80    1Mx4

        FUJITSU         MB814400Z-80    1Mx4

        NEC            uPD424400V-80    1Mx4

        OKI            MSM514400Z-80    1Mx4

        HITACHI         HM514400Z-80    1Mx4

    For the sake of confusion, some DRAMs (used in the A3000) are called
    Static Column RAMs - or SCRAMs for short. These DRAMs should work in
    the SCRAM 500, but will not improve the performance. They are better
    off in an Amiga 3000 where they will do some good! The SCRAM 500
    derives its name from SCsi RAM and has no other connection with any
    other Static Column RAM chip living or dead. Do not be confused!

    People who upgrade their A3000 machines to Static Column DRAMs may
    be a co-operative source of 4 Meg ZIPs for a SCRAM 500! They have to pull
    them out like bad teeth. Seek them out.


NJJ