View Full Version : HD dying, questions on replacing

12-25-2000, 01:51 AM
Hi everybody! Hope you can shed some light...

I noticed my internal hard drive acting weird lately, so I backed everything up and ran some tests on it. Apparently, there are bad blocks/sectors on it which Drive Setup can't fix. DS will initialize it, but without low-level formatting and zeroing data. It led me to believe that the drive is on its last legs and I shouldn't try to fix it. Heck, I don't know if it could be fixed.

Instead, I'm thinking about taking the internal drive out completely. I have an external Cheetah 9 GB UW drive hooked up to a Adaptec 2940 UW card. I will put in a internal UW drive connected to the UW card.

My questions are:

1) Can I safely take out the internal hard drive out (which is set at SCSI ID 0) and not have anything attached to that ribbon besides the other internal periphals i.e Zip, Jaz, and CD? Or must I have a device attached to the ribbon and set at SCSI ID 0?

2) On the new Barracuda (probably an 18 GB UW) which I plan to get and attach internally to the UW card. How do I terminate that since I already have an external drive attached to the card?

The machine is as follows:

PowerComputing 166 MT
Micropolis 4221AV 2 GB hard drive (came with system, slowing dying)
Adaptec 2940 UW card
Cheetah 9 GB UW attached externally to card
448 MB RAM
internal Zip (SCSI ID #5)
internal Jaz (SCSI ID #4)
internal CD (Toshiba) (SCSI ID #3)
OS 8.5.1

Any help will be appreciated. This of course has to happen over the holidays.


12-26-2000, 03:14 PM

you need to ensure that the last device on your internal bus, whether it is the logic board bus or the Adaptec, is terminated. If you are pulling your drive at ID0, it's not a problem, as long as the last device, whatever it is, is terminated.

don't get confused by logical addressing and physical addressing. Logical addressing refers to the number assigned to a SCSI device using a jumper or other method. Addresses on narrow buses range from 0, typically used for narrow boot drives, to ID3, typically used for CD-ROM, to ID7, universally and without exception used exclusively for the host, meaning the SCSI card, or the logic board.

physical addressing simply refers to the order of the devices ON THE CABLE, meaning their order from the beginning of the bus (always the host), to the next device on the cable, to the next device, etc., until the last device. The last device, and only the last device, needs to be terminated.

in your case, if you pull your drive, you need to trace your cable from the logic board or your SCSI card, and confirm which device is the very last one on the cable. That device, whatever it is, must be terminated.

with your Adaptec card, you can attach an external drive or drives to it, and internal devices, but this will physically place the card in the middle of the bus. This means you must terminate the last physical device, and the last internal device. The card will automatically disable termination on itself.

just make sure that all devices on a bus have unique IDs, and never use ID7. That should cover it.

12-26-2000, 04:08 PM
Thanks magician!

I am positive that the internal hard drive is dead, so I won't be using it at all except as a paperweight. I forgot to mention that I have a CD-RW that exists as the last device on the SCSI chain (#6) is which terminated. It is not always on, but it is always terminated. Is that okay?

If I had to remove the CD-RW (for whatever reasons) that would mean my internal Zip is the last device. I assume active termination is built-in, so I should still be okay. Yes?

As for the Adaptec SCSI card, yes, the external device is terminated. As soon a I get the new internal drive in for the SCSI card, I will install it and I will set its SCSI ID to #1 (the external is set to #2).

Bascially what I will have is an external 68-pin device attached to the 68-pin external port of the SCSI card which is terminated properly. I will then attach an internal 68-pin device to the 68-pin internal port of the SCSI card. This internal device, as you explained, must be terminated.

How do I that?

Thanks for the help. :-)

12-26-2000, 08:31 PM
Hi Burgoo...it seems I've repeatedly heard Magician say DON'T have devices in the SCSI chain that are power off.

I would like to hear him or one of the guys explain this. (thinking outloud here)......I'm guessing that a termination enabled drive is only that, if powered on. Or if a device in the middle of the chain is power off, that the host see's the next device closest to it as the end of the chain and non-terminated..........Magician or ..........?, am I close? Looking to further my education.............


[This message has been edited by crazyeights (edited 26 December 2000).]

12-27-2000, 01:37 PM
ok...any device which is attached to the mac must be powered on, or the Mac and other devices attached to the bus will attempt, without hope of success, to provide termination power to them. Running with unpowered devices is akin to imposing an electrical "blackhole" on the bus, and it is not a good thing.

if the CDRW is the last device on that bus, it must be powered on, and it must be terminated, either using a switch on the backplane of the enclosure, or with an external active terminator. If you pull it, and the Zip is the last device, you must manually set the Zip to terminate the bus. There is a switch on it, and you have to physically change it.

you set termination on internal devices using jumpers on the TE (termination enable) pins. Again, only the last internal device on an internal SCSI chain must be terminated. All others must be unterminated.

a SCSI card with internal and external segments is in the physical middle of the bus, and should automatically sense the presence of connectors on its internal and external ports and disable termination on itself. Manually setting termination on the last internal device, and the last external device, correctly terminates the bus, with termination at each end.

12-27-2000, 08:36 PM
Thanks for the info, magician, I will not always turn on the CD-RW before I start up the computer. That particluar CD-RW does have an active terminator on it; I bought it from APS Tech a few years back and even though I don't always need it on, I noticed the termination light on the back is lit when I start my computer up. But following your advice, henceforth all devices attached to the computer will be powered on.

Does SCSIProbe tell the user if the SCSI devices are terminated properly? I haven't used it in years, but I remembered seeing a msg from it years and years ago when I didn't have proper termination on a device. Hmmm...

You know...before I bought the CD-RW, the internal Zip was the last physical device on the SCSI bus. PowerComputing had put that in for me. Based on what I know now, that Zip needs to be terminated properly which I believe was the factory default. So how does that change when I attach another device on the chain i.e. the CD-RW?

As for the SCSI card layout, thanks for the help on that front too, magician. I'm never concerned about external devices terminating properly. I learned that years back; I'm always cautious when it comes to internal items hence my nervousness regarding the new internal drive I'm gonna attach to the SCSI card. I'm sure the drive ships with termination enabled as factory default, but I will physically confirm that before I even try to attach it to the SCSI card. And I'll also double-check the PowerDomain Control Board to make sure that the card's termination is disabled.

I was unsure whether or not I needed to get a 68-pin ribbon with special terminators attached in order to get the drive to work. I guess that as long as the jumpers on the new drive are terminated and the external is terminated, it'll be fine.

Thanks for the info; I'll let you guys know how everything turned out.

12-27-2000, 08:39 PM
Oops! I meant to type "I will always turn on..."

Thanks again!

12-28-2000, 04:08 AM
if you get LVD drives, you will require an LVD cable with an inline terminator. LVD drives lack TE pins.

remember, the rule of thumb for internal devices is the same as for external devices. A bus is a bus, whether it is inside or outside. Simply trace your cable from the host, whether the host is a logic board connector or a SCSI card, and go all the way to the end. The last device must be terminated.

leave your SCSI card set to auto. Let it do what it knows.

12-29-2000, 01:34 PM
The drive came in and I didn't have to do anything on it at all. Termination was enabled on the jumpers (that was the default).

The only question I have is on Termination Power: whether it comes from the drive or the bus (card). The default is that it comes from the drive.

Everything is hooked up and the drive is initialized and partitioned. No errors canme on whenI started the machine several times. It seems that everything is in working order. Knock on wood.

Thanks for the help, all!

12-29-2000, 05:44 PM
Termination Power already comes from the bus/card. You don't want two sources of Term Power. Not a good thing. k

12-30-2000, 07:02 PM
So I should change the jumper settings for Termination Power so that it gets it from the bus and NOT the drive which is the default setting, correct?

My new drive is a Seagate Barracuda ST318416W. Sometimes those schematics are tough to figure out.


12-31-2000, 12:52 AM
This one is a little tough to figure out. But yes, you want Term Power from the SCSI bus, you want that jumper horizontally across the two lower pins of TP2 and TP1 in Figure 7e. k