Dead HD20

[trag]

I was looking at the Apple Service Source manual for the HD20 and they list the drive as part number 661-0373. This happens to also be the same part number as the Apple 20SC hard drive that shipped with the HD 20SC, the original SE 20MB configurations and may also be in the II, IIx, IIcx, IIci & IIfx, SE/30 & possibly Classic. So I checked the service source manuals for them and sure enough, Apple calls them "Revision A". Revision B is a different part number and cannot be interchanged with the Revision A drive. Unless Apple decided to reuse a part number, the drive in the HD20 appears to be a SCSI hard drive of a certain configuration.

Okay, time for someone to check the drive/connector on the Mac Portable and compare it to the disk drive mechanism in the HD20. The Portable used a SCSI drive with a special cable harness attached. If the number of pins matches, it is time for a more careful comparison.

It may be that Apple reused this modified SCSI connector in both the HD20 and the Portable, although, IIRC, the Portable had a 40MB drive.

The Portable pinout is avaiable somewhere, because there was a Portable to standard 50 pin converter available at some point. If the HD20 uses the same scheme as the Portable and we know the pinout of the Portable, then we would know the pinout of the HD20 and the only remaining thing to do would be to build a conversion cable so that we could test other SCSI drives in the HD20 case.

I'd check it myself, but I don't have a Portable.

 

[Charlieman]

I was looking at the Apple Service Source manual for the HD20 and they list the drive as part number 661-0373. This happens to also be the same part number as the Apple 20SC hard drive that shipped with the HD 20SC, the original SE 20MB configurations and may also be in the II, IIx, IIcx, IIci & IIfx, SE/30 & possibly Classic.

I think that there is some confusion about service manuals. That sounds like a HD20SC manual, not HD20 -- I don't think that Apple produced Hypercard versions of all of the early manuals. Service part 661-0373 was a generic number for a 20MB drive, I believe. Apple used 20MB drives from a variety of manufacturers (Sony, Miniscribe, Seagate, Rodime).

My paper copy of the HD20 manual gives part number 661-0302 for the "non-standard" Rodime disk.

In which case, it should be possible to adapt any SCSI drive to work with the HD20.

Even if the HD20 drive is a variety of SCSI, the floppy port bridge board will be model specific. It will only work with a disk with the same geometry (and possibly timings) as the original.

 

[Charlieman]

Okay, time for someone to check the drive/connector on the Mac Portable and compare it to the disk drive mechanism in the HD20. The Portable used a SCSI drive with a special cable harness attached. If the number of pins matches, it is time for a more careful comparison.

OK, OK, I'm charging my Portable for the first time in ages. It may take a couple of evenings to get it up and running reliably to do any disk testing (I want to verify the Portable's HD before proceeding).

For information, the floppy port bridge board ("HD20 Controller Board", according to the Service Manual) is part # 661-0300.

I'll see if I can find a Rodime of the same era as the one in the HD20 for comparison with JDW's excellent photos.

 

[Mac128]

Charlieman, I'll happily send you the HyperCard manual covering the Hard Disk 20. I have the HyperCard manual for both the HD20 and the HD 20SC.

Looking at the parts list, I too find the part 661-0302 which is described as the "HD 20 w/analogue board" ... it goes on to say "This IWM hard drive has a 36-pin hard drive data cable connector. The related 3.5 inch hard drive (661-0373) has a 50-pin hard drive data cable connector". It also verifies the part number you have for the controller board in your manual.

Here are the pertinent pages:

http://farm2.static.flickr.com/1228/1405361502_cd986d9141_o.png

http://farm2.static.flickr.com/1060/1405361512_e640618f4c_o.png

http://farm2.static.flickr.com/1014/1405361508_d5472d6e53_o.png

So the way I look at this is that given the specific exchange descriptions concerning the 20MB P/N 661-0373 with respect to the 20SC drives in both the OEM SE & External, is that the drive itself, Rodime or otherwise, is a specific type of drive which will work with the HD 20 analogue board. Meaning, if the drive itself is bad in an HD20 and NOT any of the boards, it would appear it's an easy swap. I base this on the fact that it lists other 20MB drives with a different part number for use in the same products. If the 661-0373 is a generic P/N it is generic to a specific application including the HD20 unless I am not reading the tech notes correctly.

I don't understand at all where anyone would get that the Mac Portable 40MB SC drive would work in the HD20 at all ... in as much as any SCSI drive would work if the appropriate adapter is used, given that's what Apple did with the 661-0373 drive ...

 

[trag]

I don't understand at all where anyone would get that the Mac Portable 40MB SC drive would work in the HD20 at all ... in as much as any SCSI drive would work if the appropriate adapter is used, given that's what Apple did with the 661-0373 drive ...

The HD20 has an IWM interface on the outside. Then it has a circuit board to translate from IWM (I.e. Mac floppy) interface to whatever interface that 36 pin hard drive connector implements.

One possibility is that the 36 pin connector implements SCSI and that the circuit board in the HD20 translates from IWM to SCSI. There are enough conductors in 36 wires to implement SCSI. Even if we knew that the hard drive mechanism in teh HD20 was a SCSI drive with a custom connector, we'd still have problems, because we have no idea what the pinout on the 36 pin connector is.

Now the Mac Portable uses a SCSI drive with a non-standard connector. If it also happens to have 36 pins, there is some possibility that Apple used the same non-standard connector for both SCSI devices. In which case guessing at the pinout becomes much easier--maybe.

But the HD20 may be something completely different. This seems pretty unlikely though. Why would Apple invent a whole different interface and then build an adapter card to it? If you buy a hard drive with a custom interface, specify that the interface be IWM already. Right? So it is likely that the interface on teh HD20 drive is actually something common, but with a non-standard connector. The choices are ST506 style, IDE or SCSI or something completely different.

Given Apple's fondness for SCSI and the fact that they stuck non-standard connectors on another drive (the Mac Portable's drive) my first guess would be a non-standard connector implementing SCSI.

 

[tomlee59]

I would be very surprised if the HD20 were a scsi device internally. For one, it predates scsi by a fair bit; even draft versions of the scsi spec did not yet exist, afaik. Even the Plus had to debut with an implementation based on a not-final draft (which is why it has some problems unique to the Plus). Even if the historical timing didn't raise questions, the engineering complexity of translating iwm to scsi, and then ultimately to what the raw drive wants makes me doubt that the design team went that route. Most engineers would have translated iwm directly. Maybe the raw drive uses an ST-506 interface, or -- given Apple's penchant for uniqueness beyond reason -- a special controller board with "optimizations" for translation to iwm. But scsi in the middle? I would be very, very surprised.

The Portable has a more or less normal scsi implementation; some ground pins were sacrificed to reduce the pin count. And a high-resistance termination is used to reduce power. Other than that, it's a plain-Jane scsi.

 

[Moofo]

I have three of those.

One is non working and one has a rare scsi conversion board. The conversion was done by a weird company at the time.

The drive id the same rodime, but the Bridgeboard brings the drive to SCSI instead of Floppy.

Oh, and one of them I got on ebay a long time ago, It had files on it. From Lockheed missiles !

 

[LCGuy]

Wow..got some pics of this board? :O

 

[Mac128]

Here is an Apple 20MB SC drive on eBay that might be a potential candidate.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230086020503&ru=http%3A%2F%2Fsearch.ebay.com%3A80%2Fsearch%2Fsearch.dll%3Ffrom%3DR40%26_trksid%3Dm37%26satitle%3D230086020503%26category0%3D%26fvi%3D1

Too bad Apple didn't put the part number on that 20MB sticker!

The board appears to have the exact same connection points as the HD20 Rodime drive and it mounts component-side up as specified in the tech manual for the 661-0373 drive.

So here's what I have been thinking: this particular 20MB SC drive is interchangeable with the HD20 IWM drive. Just swap the on-drive circuit boards. If so, then you have a SCSI circuit board from which to map out adapters for other SCSI drives to be used in the HD20.

The fact that dropping in a new Personal Computer Peripherals Corporation circuit board would convert the stock HD20 drive to SCSI (http://docs.info.apple.com/article.html?artnum=3449) and substantially increase the speed (according to Apple), means the information transferred from the drive itself can be converted to SCSI at close to SCSI speeds. It was called the HD-20 WSI ("Woz SCSI Interface"?). I wonder if you would even need that circuit board if you swapped the analogue board on the drive for a compatible SCSI one? (a much more difficult prospect for the DIY customer)

Hey Moofo, we really needs some pics of that card and how it was implemented!

 

[Moofo]

The drive is in my hometown !

I will bring it back though, even if it's broken.

It'S really an odd mod...

I also have pretty saucy cards in my IIgs, such as a 286 card...

 

[Moofo]

I found this in my old old old old newsgroups posts:

>The Apple HD20 used a DB-19 connector on an olive-colored cable. If

you

>have a DB-25 connector on a gray cable, you probably have the

conversion

>kit that somebody (MacBottom?) sold to convert the drive to the

world's

>slowest 17 megabyte SCSI drive.

It was from someone in a university (biomath.mdacc.tmc.edu) to answer the question I asked at the time about that drive

 

[numero6]

About :

Hey you guys with 20MB HD-20SC external drives ... you mind cracking those cases open and reporting on the drives living in there? The reason I ask is because one of the two variants of 20MB drives is supposed to work with an HD-20 IWM drive as discussed here: http://68kmla.org/forums/viewtopic.php?p=20427#20427
The one with components facing up (not the solder side) is supposed to be the one. Pictures would also be appreciated as I've looked all over the internet and nobody seems to have taken pictures of the internal workings of a "STOCK" HD-20SC, like JDW did with his HD 20. Thanks!

Here are some inside pictures of my SC20 :

 

[lee4hmz]

Looking at the pictures on Flickr, I notice the drive itself has an Adaptec AIC-270 RLL codec and a Ferranti ULA5R-series semi-custom chip on it, both common hard disk controller components in the late 1980s. Digging around in Google, I found some interesting tidbits in the patent search:

US Patent 4,757,406: High capacity disk drive

http://www.google.com/patents?id=mvs7AAAAEBAJ&printsec=abstract&zoom=4&dq=ferranti+ula#PPP1,M1

The patent describes a drive that looks exactly like the HD20 unit, with the same chips and an NRZI interface (I'm guessing specific to Rodime) that looks a lot like ESDI. It also includes what appears to be complete schematics for the HDD's logic board.

 

[Charlieman]

During testing for another thread (the one about Zip drives on a Plus), I dragged an old Rodime 20MB SCSI drive out of retirement. It ran very well, thank you, and I cracked it open for a few photos. No time to publish the photos this evening, but it is nothing like JDW's photos of an HD20 guts. The underside of the 20MB SCSI drive has a lot less chip density, but has a 50mm square Adaptec SCSI chip. I'll post the photos and review JDW's pictures.

 

[JDW]

numero6, that's a lot of rust on your HDSC frame!

I have an HD20SC that I bought off EBAY to use with my IBM DGHS 4.5GB 7200rpm hard drive mechanism. It worked beautifully to allow me to remove that hot drive from the inside of my SE/30 to the HDSC20 enclosure (which I did to decrease the overall heat inside my SE/30 -- much of which came from the hard drive). With a MacCon ethernet card, 128MB RAM and a 50MHz DiiMO accelerator, my SE/30 got quite a bit cooler after moving out the hard disk. Anyway, the insides of my HDSC are not nearly so rusty. Slightly discoloration here and there is all I see, but definitely no red rust! Your drive must have been used in a sweat shop!

 

[tomlee59]

Digging around in Google, I found some interesting tidbits in the patent search:
US Patent 4,757,406: High capacity disk drive

http://www.google.com/patents?id=mvs7AAAAEBAJ&printsec=abstract&zoom=4&dq=ferranti+ula#PPP1,M1

The patent describes a drive that looks exactly like the HD20 unit, with the same chips and an NRZI interface (I'm guessing specific to Rodime) that looks a lot like ESDI. It also includes what appears to be complete schematics for the HDD's logic board.

That's a great find! I'm amazed that the patent drawings are basically the engineering drawings used to make the actual drive. And schematics, too!

 

[JDW]

I just had a look at the patent myself. Quite stunning. Compare Fig. 5 (Rev. 2 drive diagram) in that patent to my photo of the bottom of an actual Rev. 4 drive (used in my HD20). Almost exactly the same!

With all the technical detail in that schematic, it would appear that one could build a hardware interface for flash drive (to be used in an HD20)!

 

[lee4hmz]

I just had a look at the patent myself. Quite stunning. Compare Fig. 5 (Rev. 2 drive diagram) in that patent to my photo of the bottom of an actual Rev. 4 drive (used in my HD20). Almost exactly the same!
With all the technical detail in that schematic, it would appear that one could build a hardware interface for flash drive (to be used in an HD20)!

The one thing that might be trouble is the serial interface the Z8 on the drive and the Z8 on the HD20 bridge board are using to send commands. The patent doesn't really elaborate on the protocol. That said, it's low bit-rate serial using, if anything, RS-232/422 framing, so it should be easy to figure out. I would guess the bridge board sends the drive CPU the cylinder and head to seek to, retrieves status, and then hits the gates and reads or writes the appropriate sector(s) using the NRZ line. The drive may also have a magic incantation for FORMAT UNIT, something the patent hints at.

Since the drive itself is 2,7 RLL, I wonder what they're using that IWM for. Has anyone traced the bridge board yet?

 

[numero6]

numero6, that's a lot of rust on your HDSC frame!
I have an HD20SC that I bought off EBAY to use with my IBM DGHS 4.5GB 7200rpm hard drive mechanism. It worked beautifully to allow me to remove that hot drive from the inside of my SE/30 to the HDSC20 enclosure (which I did to decrease the overall heat inside my SE/30 -- much of which came from the hard drive). With a MacCon ethernet card, 128MB RAM and a 50MHz DiiMO accelerator, my SE/30 got quite a bit cooler after moving out the hard disk. Anyway, the insides of my HDSC are not nearly so rusty. Slightly discoloration here and there is all I see, but definitely no red rust! Your drive must have been used in a sweat shop!

Not exactlly a sweat shop : it stood many years in a barn ! N o direct rain but a lot of humidity ; its owner didn't care very much after him, that's why he gave me the drive and the Mac Plus for free...

The disk is a Miniscribe, but it must be rusty inside too as it doesn't work. I can't even reformat it although it is detected when I plug it to my Performa.

 

[Moofo]

Hey guys...

Pics of my HD20 SCSI conversion board

I heard this is pretty rare !