Dead HD20

[JDW]

Wow! Where did you find one of those? (Well, I will assume EBAY and the seller didn't know what he was selling.)

Does it work well? And on what Macs have you tested it? The hard drive mechanism isn't shown in your photos -- is it the stock Rodime?

 

[Moofo]

I got the HD-20 with the board inside a long time ago (7 years ?). I never got it to work, either because I don't have the drivers or it is broken.

It is the same stock rodime drive as my two other Hd20...

I suppose the dip switches are used to set the ID and options...

 

[Mac128]

Thanks for that. A great piece of documentation. Interesting that it uses the Platinum coloured-cable with the original khaki pre-platinum design. Got to be one of the only SCSI cables ever made with that connector design. More interesting than that is the old floppy-connector opening appears to have been manually enlarged to accommodate the wider SCSI pass-through. Is there evidence of it being done with some kind of knife, or a more professional Dremmel tool?

As for the DIP switches, yeah pretty much must be the SCSI ID settings and pass through ID's. I'm amazed it doesn't work. Surely it's an ID issue. Seems to me the original HD x0-SC drives had a similar dip switch configuration. Maybe the Apple Archives ... I'll pull the tech manual and see if it's helpful.

I wonder if there's enough detail on that board to construct one from scratch. Remarkably sparse compared to the original IWM board, isn't it?

 

[Moofo]

The hole is not enlarged. You just don't get to use the thumbscrews.

I'll try to hook it up to a mac with no internal HD and get back to you...

I **may** try to switch the controller with another HD20 to test.

 

[Mac128]

Moofo, yes, my dead HD20 is in the drive mechanism, not the controller board, which works with my good drive. So if the drive is bad, then of course it wouldn't work.

No thumbscrews, eh, so you can't secure the cable. Probably best. I never guessed that the SCSI controller board would have a pass-through. I always figured it would be an end of chain solution. Much more elegant interface than Apple's bulky 50-pin connectors. Too bad they didn't included a SCSI interface as well so the drive could be replaced with a real SCSI drive if it died.

I checked the service manuals and the older Apple drives used jumpers not DIP switches, sorry about that. In addition to ID DIPS, the three yellow resistors behind the pass-through connector should be the removable terminators, which are identical to those in the early Apple drives.

When you get a chance, would love to see the bottom side of that board as well.

 

[Charlieman]

When you get a chance, would love to see the bottom side of that board as well.

The upper side photos are almost enough to create a schematic, I think. It just looks like a single layer, single sided board. The chip with a handwritten lablel appears to be an EPROM. With the EPROM code, the board can be replicated and possibly modded to work with other drives.

 

[Mac128]

The upper side photos are almost enough to create a schematic, I think. It just looks like a single layer, single sided board. The chip with a handwritten lablel appears to be an EPROM. With the EPROM code, the board can be replicated and possibly modded to work with other drives.

Ah, the old EPROM problem. Meaning, there's some kind of custom code that translates the IWM to SCSI?

Actually, in rethinking it, creating more SCSI controller boards is not the most practical idea, since one can drop any old SCSI drive & controller in the box and most likely tap off the Sony power supply.

I think the more interesting idea is to reverse engineer the board so as to use it to convert backwards from the original IWM controller board to a new SCSI disk, considering the IWM disks themselves seem to be the weakest link in HD20 failure. This way the HD20 can still be used with a stock 512K/e once the IWM drive dies.

 

[lee4hmz]

Here's what I'm seeing:

* The PCPC HD20 SCSI board adapts normal Mac SCSI to the Rodime proprietary interface used by the drive. It's only really useful with the original drive.

* Now that I've had some time to think about it, I can take a better guess at what that IWM on the stock HD20 bridge board is actually doing. What makes sense to me is that it's using the IWM as a high-speed UART -- think "LocalTalk over the floppy port". If we could see how the IWM is wired to the Z8 on that board, it would help a lot. The next step after that would be rigging a microcontroller and glue logic to talk to a hard drive (it wouldn't really matter what kind, though IDE would be simpler than SCSI and would open the door to a CompactFlash solution).

-lee

 

[Mac128]

* The PCPC HD20 SCSI board adapts normal Mac SCSI to the Rodime proprietary interface used by the drive. It's only really useful with the original drive.

Here's what I'm thinking. If I had that SCSI board, I'd try this in an instant:

1. Normal Mac 512K DB-19 to IWM board connector.

2. MOD: IWM board Rodime connector to SCSI board Rodime connector.

3. MOD: SCSI board connector to SCSI drive.

My thinking here is this, if the SCSI board is translating IWM data for the Rodime drive and it's not just one way. Since the IWM board is already talking Rodime language, it doesn't really matter if it's from the drive or the Mac. So you use the DB-25 SCSI-to-Mac connector in reverse to attach to a SCSI drive. You've still got disk commands coming in from one side and drive data from another.

Then again, I'm no electrical engineer.

 

[Mac128]

Hey Moofo, does your SCSI interface cable look like this one on a MacBottom:

http://www.flickr.com/photo_zoom.gne?id=2232718747&size=o

Can you confirm whether it matches the original 128K/512K cables, or whether it is actually Platinum?

On looking at your picture again I find it hard to tell if the colors are accurately reflected in the photo. What is interesting about both, particularly the Bottom is that they used the almost identical Apple cable design without the actual Apple logo in the recessed square, or on the ends of the thumb screws, perhaps made by the same manufacturer?

I would imagine both of these products would have come out in early '86 before Apple's first SCSI drive, in which case the cables should match (not that they couldn't have come out afterwards), but then why use the old style connector?

 

[Mac128]

Question about the DB-19 Daisy-chain connector built-into the HD-20.

The logicboard has on it a PAL 16R6 device, which on the original Macintosh performs the TSG clock splitting duties. It also contains a 7.5MHz clock.

My question is this, on the original Macs, pin 10 of the external connector contains the PWM signal regulated by the PAL ASG 16R8 device. Now, does the HD20 ignore that signal and reproduce its own signal depending on what's connected to its daisy-chain port? Or simply, just what is that clock and PAL doing in the HD20?

Unlike a 400K drive, the HD20 can be connected to a SWIM-based Mac which sends out a +5v signal on pin 10 of the external connector. But Apple says you can connect an FDHD external drive to the back of the HD20. So, if the HD20 didn't incorporate that signal option into its logicboard design and it doesn't pass through pin 10, does the FDHD even need that +5v signal? I noticed the Portable also does not supply a signal of any kind on it's external floppy connector.

If the clock and PAL are there to provide PWM signal to the external floppy connector, I would think it would also support a 400K drive when the HD20 was connected to an SE FDHD or Classic or other SWIM Mac, when connecting them directly to the SWIM Mac would probably fry the drive.

 

[Moofo]

The cable is exactly like this.

 

[Mac128]

on the original Macs, pin 10 of the external connector contains the PWM signal regulated by the PAL ASG 16R8 device. Now, does the HD20 ignore that signal and reproduce its own signal depending on what's connected to its daisy-chain port? Or simply, just what is that clock and PAL doing in the HD20?

I answered at least part of this ... the HD20 seems to pass through whatever signal it receives on pin-10. It generates no signal when disconnected from a Mac.

So now I'm onto does the FDHD NEED the +5V output since when connected to a Mac Portable pin 10 is disconnected? If an FDHD can be used on an IWM as an 800K drive, it stands to reason it uses pin 10 to determine whether it's connected to an SWIM Mac or not. Otherwise, the data signals are identical.

ALSO: on a 400K floppy, does pin 10 on an IWM Mac simply provide a clock pulse from which the drive measures its speed variance? If not how does that drive use the PWM signal (which shows up as a fluctuating 2.5v signal)? I'm assuming an 800K drive which regulates it's own speed has it's own clock crystal from which to regulate speed? Couldn't the same thing be added to a 400K drive?

Finally, why does an HD20 have a clock chip, PAL and IWM?

 

[JDW]

You know, I believe I read through Mac128's post above last year, but I skipped past the part about the SCSI conversion for the Apple HD-20. I was led back to this thread, however, after listening to a recent RetroMac Cast which talks about the WSI product.

Since I have had no luck whatsoever in finding a software solution that would allow my SE/30 to read my HD-20 drive contents, I would absolutely love to get my hands on one of these WSI upgrades in order to make it compatible. Not just compatible but also fast-and-compatible! But alas, I've never seen anything like this on EBAY, so I am wondering if one of these devices will ever surface. They probably have been sold on EBAY with the seller not knowing what he sold (and perhaps the buyer not knowing what he bought).

 

[Bunsen]

A guy I'm buying some other stuff from has a Macbottom listed at $7.95. As usual, shipping kills it for me, so go nuts. If you end up stripping it for parts and are wondering what to do with the empty case ... PM me

 

[Mac128]

A guy I'm buying some other stuff from has a Macbottom listed at $7.95. As usual, shipping kills it for me, so go nuts. If you end up stripping it for parts and are wondering what to do with the empty case ... PM me

What are you going to do with the empty case?

I have one of these, it's the model with the built-in modem. Very clever, though they really didn't go the extra mile in case design. Hate the seam right across the middle of the case. Aside from that small flaw, it's a far superior design to the HD-20 & SC cases which are almost an inch taller and deeper.

 

[Charlieman]

Aside from that small flaw, it's a far superior design to the HD-20 & SC cases which are almost an inch taller and deeper.

From previous threads we can read that Apple were happy to buy hard drives from the cheapest seller. A further assumption is that they designed their enclosures with expansion in mind, including tall drives. And if Apple had offered me a really fat 160MB drive in the 20SC enclosure, I'd have asked my boss to buy one.

Instead, he bought me a 160MB Rodime in a slim case. It never failed me and it looked nice.

 

[Bunsen]

What are you going to do with the empty case?

Horrible, horrible things. MUAHAHAHAHAHAHA!!!

I'm looking for an aesthetically appropriate external expansion box for an SE/30 project machine.

 

[transcorpmla]

If you still have the HD20, would you like to sell the case?