Mac Crate 40MB External Hard Drive info and repair

Elemenoh

Active Tinkerer
Oct 18, 2021
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I recently found a Mac Crate 40 MB external hard drive. It looks kind of weird, as if it were an accessory for an IBM instead of a Mac. The line of hard drives seems to have been launched in 1988 based on this ad in MacWorld from that year.

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The model I found is 40 MB and in fairly good physical condition other than a yellowed plastic bezel.

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One quirky thing about the drive is that it has two DB-25 connectors rather than more typical 50-pin Centronix connectors. SCSI ID is set with jumpers. Because 25-pin terminators are uncommon, I'm using a BlueSCSI as the terminator.

+-------+---------+ |SCSI ID| 4 2 1 | +-------+---------+ | 0 | o o o | | 1 | o o x | | 2 | o x o | | 3 | o x x | | 4 | x o o | | 5 | x o x | | 6 | x x o | | 7 | x x x | +-------+---------+

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Unfortunately when I turned it on, a resistor in the PSU blew within just a couple of seconds. I have no idea what value it is. Rather than try to figure that out, I found a cheap ($14 USD) 12V/5V power supply on Amazon that was a bit smaller than the original power supply and seemed like it'd work with the existing standoffs if they were relocated. After drilling some new holes and snipping the leads, it worked perfectly.

Original PSU:
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Replacement:
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Inside things are also a little odd. There's a 10 position IDC cable connecting the SCSI ID pins on the hard drive to the external pins. There are only 6 pins on that board side and no keying on the cable.

Also, the notch side of the SCSI cable is in the normal orientation on the drive itself, but actually needs to face the other side on the connector board.

The drive itself is a full height 40MB Seagate. There's a handwritten note on it that it's price new was $239. Either someone got a great deal or purchased this drive late in its life.

Oh one other weird thing. The enclosure was designed for a face plate to be screwed into the hard drive bracket. But this faceplate doesn't line up with those holes and was clearly just glued on at the factory. It was loose when I got it, so I glued it down with epoxy.

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Since replacing the PSU, the drive has been working fine. It needed a few bad blocks marked off and a couple of viruses cleared up. Now it'll be a go-to drive to pair with early compact Macs.
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Elemenoh

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The face plate has a LED diffuser but there’s no apparent header for it on the drive mechanism. For now I just connected a small green LED with a 100ohm resistor to +5V so at least it does something.

Should it be possible to tap into the SCSI IO to make an activity LED?
 

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Elemenoh

Active Tinkerer
Oct 18, 2021
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Is there not a pair of pins for an LED somewhere on the drive?

Also, find anything interesting on it? :D
There is a pair of pins on the front side of the controller, but it’s 0V all the time. The manual for the Seagate drive itself refers to a diagnostic that uses a LED thats enabled by shorting some of the SCSI pins to ground. There’s nothing in the manual about a general activity LED.

And nothing special other than a Mac Crate drive icon. I should archive that somewhere.
 

Elemenoh

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Oct 18, 2021
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I always wondered why many SCSI terminators are dual sided/gendered. Apparently it’s to help terminate further up the chain as needed but also works perfectly to terminate this drive using a typical 25-to-50 pin cable.

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ScutBoy

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Sep 2, 2021
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With SCSI, there's where the terminator should go, and sometimes where it needs to go to make everything work. They are often not the same...
 

retr01

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Jun 6, 2022
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Hey @Elemenoh, I like this picture of the Mac Plus with POV looking up from below. :D(y) I nabbed it for one of my photo projects. I have a lot of projects going on. LOL! 🤪

Now, I just need to make it look much more intimidating.

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epfd

New Tinkerer
Feb 6, 2024
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Hey @Elemenoh, thanks for the post. I have a 60MB Mac Crate that failed to power up. $15 for that power supply did the trick. It’s back up and running thanks to you!!
 
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lilliputian

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Mar 6, 2022
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Hi @Elemenoh, just got myself a MacCrate as well. The power supply of mine came dead, with a blown resistor at R4 and a dead fuse. I'm going to try and fix it, hopefully it was just those two elements. Hopefully I can find a photo of a functional PSU to read the resistor value...

PS. Mine came with a full-width hard drive, Seagate ST-296N, so the mounting holes do line up correctly for the faceplate (which was damaged in transit; fortunately all the pieces were recovered).

And thank you for the photo of the SCSI ID alignment, mine was disconnected on arrival!
 

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