myoldmac.net
- Mac 68k F.A.Q.
Macintosh Portable
Internal SCSI Cable
by Steven M. Schweda
Original source URL: http://antinode.org/mac/port_scsi.html
Macintosh Portable Internal SCSI Cable
The adapter cable described in this document
allows a normal SCSI disk drive (with a normal,
narrow SCSI, 50-pin connector) to be connected
to the 34-pin internal SCSI connector in a Macintosh
Portable computer. It allows the original (40MB)
disk drive to be replaced by a more readily available
(and higher capacity) drive.
Only a low-profile drive will fit in the physical
space, and the power requirement for the replacement
drive should be fairly close to that of the original
drive, to avoid damage to the power supply in
the computer.
For example, the power rating for the 80MB Quantum
ProDrive ELS (5V 230mA, 12V 135mA) is lower than
that of the original 40MB Apple Hard Disk 40SC
(Conner CP-3045, 5V 275mA, 12V 250mA). Normally,
on the two-row 50-pin connector, odd pins 1-23
and 27-49 are ground, and pin 25 is not connected.
In this adapter cable, the connections 2-47,
6-49, 11-39, and 16-5, are opportunistic grounds,
easy to make with paired conductors in the 34-conductor
ribbon cable. Attach the 34-pin connector to
the ribbon cable last, as this makes it easier
to get the cable length correct.
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