HELP! My HD20 SC won't work!

#1 Wed, 4 Feb 2015 - 02:47 68kMLA

I have a HD20 SC that works great when attached to my SE, but will not boot up either one of two Mac Plus machines. The manual says I need the "Hard Disk 20SC Installation Disk". Anyone happen to have THAT one laying around? Thoughts? Thanks!

_Stephen White

#2 Wed, 4 Feb 2015 - 03:25 68kMLA

I think what you mean is the HD SC utility which is used to format and probably check/verify the drive.

If it's working on your SE, I'd be surprised if it wasn't working for software reasons on the Plus. (Termination?) I'd be surprised if you needed HD SC to boot. (http://en.wikipedia.org/wiki/Apple_HD_SC_Setup)

#3 Wed, 4 Feb 2015 - 03:43 68kMLA

Termination is a likely culprit.

Have you replaced the internal drive mechanism? You may need to modify it to work properly as an external drive, then make sure the termination on the drive itself is right. On many drives, you'll need to remove some jumpers to use them externally (and with an ID switch).

#4 Wed, 4 Feb 2015 - 04:20 68kMLA

Actually I'm going to backpeddle on the termination thought. For use in the SE, it should probably have been terminated properly. (Unless maybe those two rubber-coated terminator resistors are dead.)

Do you have any other SCSI devices attached to the Plus?

#5 Wed, 4 Feb 2015 - 05:28 68kMLA

(*3 terminator resistors)

#6 Wed, 4 Feb 2015 - 05:40 68kMLA

It boots on the SE without a terminator. I know very little about all this. Would a scsi terminator help?

#7 Wed, 4 Feb 2015 - 05:59 68kMLA

Can you describe the symptoms a little more?

Someone will know way more than me but the first step should be booting the Plus with HD connected using any disk tools disks you have.

If you can port stuff from the Internet, you will probably eventually want HD SC, which I can email you (in a disk tools disk image) if that will help. And then SCSI Probe if it will run which I cannot confirm as it has not been able to run on my SE for some reason.

(http://www.macintoshgarden.org)

#8 Wed, 4 Feb 2015 - 06:10 68kMLA

So on the SE it boots no prob. On both Pluses, it doesn't boot at all. I can boot to a disk tools disk and I have HD SC but when I run it, it doesn't recognize any scsi devices.

#9 Wed, 4 Feb 2015 - 06:46 68kMLA

I didn't realize that the HD20 SC was a genuine external, sorry. I thought you meant the SE's internal Miniscribe.

**

https://68kmla.org/forums/index.php?/topic/10576-mac-plus-and-external-scsi/

The Plus lacks internal termination of the SCSI chain. So you will need to terminate the external with a terminator on the back (I think?).

The internal drive on the SE terminates the SCSI chain, whereas without any SCSI devices by default the Plus does not.

#10 Wed, 4 Feb 2015 - 15:30 68kMLA

Ahhh I see! I will try a scsi terminator. Thank you very much!