SCSI termination headaches

[bigmessowires]

I've got a SCSI drive that works fine as an internal drive, but is unhappy externally. I put it in an old SCSI enclosure that used to contain a DAT drive. The enclosure is connected to the Mac with a 6-foot DB-25 to Centronics 50 cable. This drive is the only external SCSI device. The Mac doesn't see the drive at all, but if I run Lido 7, it reports a phase read error at SCSI ID 1 where the drive is. I've tried it with the built-in drive termination on and off, and with and without an external SCSI terminator.

Possible explanations I can think of:

- The SCSI enclosure wiring is somehow bad

- 6 foot is just too long for a SCSI cable

I'm not sure what to try next, since neither of those sound too likely. Maybe try again with an 18 inch cable, if I can find one?

 

[PowerPup]

It sounds like it could very well be the cable. I assume there's no internal HD to conflict with? Can you make the SCSI ID any higher on the enclosure?

 

[bigmessowires]

It turns out it actually was the enclosure. I overlooked some kind of SCSI extension cable it's got internally: a 4-inch 50-pin male to 50-pin female cable. A couple of the wires on that extension looked kinked, and anyway I didn't need it, so I just removed it. Now the drive works fine on my LC II and my Power Mac 8500, but still isn't recognized by my Plus. My guess is the finicky SCSI in the Plus won't work with that 6 foot SCSI cable, so it looks like I'll still be shopping for a shorter DB-25 to Centronics 50 cable.

 

[Trash80toHP_Mini]

IIRC, something on the order of 18 feet (5 meters?) is the maximum SCSI chain length according to the ACTUAL SCSI spec, heaven knows how Apple might have borked that along with the shredding the ACTUAL SCSI connector spec.

Some basic SCSI Voodoo troubleshooting steps:

Determine if the termination on the external case itself set to ON or OFF? :?:

Sometimes there's a clear window on the bottom of the case that shows if the termination resistor SIPs are installed or not.

Did you remove/disable the ex-internal, now external, drive's SCSI ID Jumper? :?:

IIRC, internal drives are set normally to SCSI ID 0, the Mac Controller being SCSI ID 7 on the 8 ID SCSI spec. or the reverse If I don't RC.

Having the external set to 0 with the enclosure set to 1-6 would very likely cause all kinds of SCSI Voodoo!

With which of your Macs are you testing your cobbled together External Drive? :?:

As an aside:

IIRC, internal SCSI Optical Drives are set up at SCSI ID 3 by Apple, so, gots CD in the box? :?:

That's all that comes to mind ATM, post some more info and maybe something else will shake loose after I've had the rest of my coffee and jangle the 'ole gray matter's convolutions with a bit more data input! [] ]'>

Edit: I see you were posting while I was! :lol: