SPECIAL MACINTOSH SCSI CONSIDERATIONS

By Howard A. Schmidt,

For those of us that have the pleasure of doing Mac cases we all know first hand what "VOODOO SCSI" is all about. This document should help those of you who are still waiting to get zapped. As complex (or easy depending on your perspective) SCSI becomes there are always those little distractions that make dealing with them more challenging. Some of the Macs require special attention, some Classics, Quadras and PowerBooks can cause problems. The IIfx above all causes some unique problems so we will start with that one.

IIfx
The terminator for the IIfx is black and physically looks different from the standard gray terminator. The IIfx terminator should cost about $20 from third party vendors. (See list of possible vendors at the end) If the Iifx has a third party (non-Apple) hard drive installed internally, there are some special issues to deal with. Normally these drives come with a resistor pack that provides termination. Even with this built in termination you still need a special filter for proper termination. To achieve this you must plug the SCSI cable directly to the logic board in the Iifx and place an internal SCSI filter (Apple P/N 590-4516) between the cable connector and the hard drive. If for some reason you remove the internal drive (or someone else has), you should install both the Internal SCSI filter AND an Internal SCSI termination Block (Apple P/N 590-4515) If you are out on a site and find yourself without the internal termination block you can insert a regular passthrough terminator at the beginning of your SCSI chain and make sure there is a black terminator at the end.

Quadra 700 & Mac Classic
If you have either one of these systems you should install an internal device (Apple P/N 630-0408) Like the fx terminator it plugs into the logic board.

Quadra 900 & 950
The 950 comes with two SCSI controllers, internal and external. The internal terminates at the logic board and at the end of the ribbon cable. Because of this ANY internal drive must have their internal SCSI resistor termination removed as the termination takes place with the cable. For cases where you are not sure whether or not the Hard Drive comes with termination or are not sure of the resistor packs location contact the Hard Drive manufacturer for technical support. (There is a freeware file on the schmidt.org FTP site called TEKSUP.ZIP that has a various tech support numbers.)

Powerbook & Duo
These popular notebooks have a very sensitive SCSI bus. To minimize problems keep any cable lengths as short as possible. Don't forget the powerbooks require the HDI-30 SCSI adapter so if you don't have one, grab one now.

I hope this helps with some of the SCSI problems we face every time we run into a Mac system. If there are any questions feel free to contact me

Howard A. Schmidt - 425-936-3890

510-471-6442 415-461-2227 800-554-3945 816-483-6100

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