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Help with HD20SC

bunnspecial

bunnspecial

macrumors G3
Original poster
May 3, 2014
8,376
6,511
Kentucky
I've struggled with getting my Mac Plus to boot with its "funny" SCSI over an external for a while, and I finally broke down and bought a 20SC.

At least the Plus sees the 20SC, which is a good start. When I first booted the computer(using a System 6 "utilities" disk) with the 20SC connected, I was prompted to initialize the HDD. There were no errors and it reported successful initialization, but the drive doesn't seem to mount. Disk First Aid will see the disk and find no errors, while HD20SC set-up crashes when I try to launch it.

Every time I reboot the computer, it reports that there are repairable errors on the HDD and will report successfully repairing them, but it still doesn't mount.

The seller had tried the disk with a couple of newer Macs and reported that the drive mounted but was unable to get it to format or to copy files to/from it.

Can I guess-based on all of this-that the drive is on the way out? If so, I have a couple of 320mb Apple OEM disks that I know will work-should these work as replacements in the 20SC case?
 
Is it the 20sc that is scsi or the floppy version? If its the floppy port version your out of luck. If its the real scsi version david is correct.

Also look up biggmessowires and the floppy emu that can do hard disk or floppy funtions and can be used by modern pc's to load images on it to use.
 
Thanks guys.

The 20SC is the SCSI version. I have an HD20 that I use with my 512Ke, and fortunately it still works well.

In any case, I pulled the case apart last night and removed the original hard drive-a monster of a half-height 5 1/4" Seagate drive. I installed a 120mb Apple OEM drive I had lying around(IBM branded). The bracket in the 20SC is drilled for 3 1/2 drives, but the ID selector on the back would not connect to the jumper array on the drive I installed. I set it for ID 0 with termination off, but I was back at square one as the Plus wouldn't see it. I used the exact same connection set-up as allowed the drive to be seen earlier-specifically a DB-25 to Centronics-50 that then connects to an Apple branded pass-through terminator and then into the top port of the 20SC. I confirmed the set up as good by connecting it to my 6500, but again no action on the Plus.

I know that the SCSI implementation is not fully standard compliant on the Plus, and have previously experimented with different termination combinations(and a complete lack of termination). As I said, the pass-through worked with the original drive in this enclosure, so I'd hoped I at least had a working connection/termination set-up. The only difference I can think of is that(per the selector on the back) the old drive was set at ID 6 and, as I set, the new one was set at ID 0. Could this possibly make a difference? I have experimented with other IDs in the past to no effect, although I don't know if the Plus itself automatically assigns an available ID or if it's fixed at one particular ID.
 
I would not use ID 0. Try 3 or 4. And of course you wouldn't expect the drive to just magically mount when you boot the Mac - you'll need to use SCSI formatting software to partition and format it before that is going to happen.
 
What's the model of the IBM drive? WDS-Lxxx, WDS-XXXx or a DSAS-xxxx ?

Looking over some older documentation doesn't seem to show a 120MB IBM SCSI, but rather a 160MB IBM SCSI.

Pic of the drive's logic board would also help.

The newer IBM drive may need "disable unit attention" jumper set.

You may want to try using Apple HD SC Setup to format the original drive. If it's quitting, you might need to find a different version.

If possible, using SCSIProbe to check if the drive's model number shows correctly can often help identify SCSI BUS problems.
 
Last edited:
MacTech68 said:
What's the model of the IBM drive? WDS-Lxxx, WDS-XXXx or a DSAS-xxxx ?

Looking over some older documentation doesn't seem to show a 120MB IBM SCSI, but rather a 160MB IBM SCSI.

Pic of the drive's logic board would also help.

The newer IBM drive may need "disable unit attention" jumper set.

You may want to try using Apple HD SC Setup to format the original drive. If it's quitting, you might need to find a different version.

If possible, using SCSIProbe to check if the drive's model number shows correctly can often help identify SCSI BUS problems.
Click to expand...

Thanks-sorry I was wrong on the capacity. It is 160mb.

IMG_2953.jpg
IMG_2954.jpg


Unfortunately, I don't have a copy of SCSI probe. The suggestion to try a different version of HD20SC is a good one-I think I have another version(separate from the one on the System 6 disk set I'm using) on a ZIP disk here somewhere that I can format in another Mac.

David Schmidt said:
I would not use ID 0. Try 3 or 4. And of course you wouldn't expect the drive to just magically mount when you boot the Mac - you'll need to use SCSI formatting software to partition and format it before that is going to happen.
Click to expand...

Thanks-I'll see what if another ID helps.

I know the HDD won't magically mount, but none of the initializing utilities I have even see it(I've confirmed the drive itself as being good). Also, my experience with System 6 is that when an unformatted or otherwise unreadable disk-whether HDD or removable-is inserted, the computer will prompt you to initialize the disk.
 
SCSI 0 is traditionally the boot device, but Macs have always been pretty good about seeing whatever is on the chain as long as it's not colliding with anything else and properly terminated.
 
Alright, here are some progress reports

1. I set the 160mb drive to ID 1 using the on-board jumpers

2. I'm using HD SC Set-up 7.3.5(or is it 7.5.3?) downloaded from Low End Mac. I've used both their patched and unpatched versions

3. Both SCSIProbe and HD SC see the drive correctly at ID 1

4. Hitting "test" in HD SC results in a couple of minutes in reading to and writing from the disk, although I ultimately get a fail

5. Initialization in HD SC also fails.

6. I've tried playing with termination. As I mentioned, the drive came to me with a DB-25 to Centronics 50 cable and an Apple pass-through terminator. I hooked it up exactly like that. I've also tried both the pass-through and a couple of other terminators on the other port of the HD SC. Of course, I did remove the pass-through terminator when terminating the other port on the drive. The only thing I haven't tried is the internal terminator on the drive.
 
I'm going to say the drive is bad - You may be able to rescue it with HardDiskToolkit Full retail (non OEM version), if you purge the grown defect list when running a low-level format, followed by a 48 hour random read-write test.

I've done that with a few SCSI drives and managed to resurrect them. YMMV. :)
 
Thanks...that's what I was afraid of.

I bought three of these drives back in October and they were warrantied. This is the first time I've taken this particular one out of the package.

The only problem is can't find the warranty terms...I'm going to shoot an email to the seller(they still have some listed on Ebay) and see if they're willing to replace it once I've made absolutely sure it's indeed bad.

I have one more from this same lot(all the others have been fine) so I'll see what happens with that as well.
 
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