Thread
Dead HD20
I have a Macintosh HD20 that came with my Plus, and it doesn't seem like the drive itself has stood the test of time.
When I boot up my Plus with the drive turned on it will attempt to boot from it, and then fail.
I eventually gave up on it, used my Centris to burn some System 6.3 images and boot the Plus that way (which took like 10 times of inserting the Utilities disk, not entirely sure wth was causing that :O )
Once booted with the HD20 connected and turned on, System 6.3 recognized it, and immediately tried to mount it. It failed, and wanted me to initialize. At first I canceled, because a label that came with it claimed it had the OS and several nice apps already on the drive. I attempted to run Disk First Aid (I think) to try and solve the problem, thinking all this time in storage had simply caused some bad sectors.
Turns out that it couldn't fix whatever error was happening, so I just decided to initialize it and be done with it. This, unfortunately, also failed miserably, it won't initialize.
The controller card does seem to be fully functional though, as it does obviously spend time trying to read the disk. I thought I felt vibrations on the disk itself when I tested it earlier, so I don't know what to think.
Does anyone know of another program that may be able to get this drive working?
If the drive is indeed dead, is there any place that still services these hard drives, or would I be doomed to trying to find one on eBay D:
-Academician
When I boot up my Plus with the drive turned on it will attempt to boot from it, and then fail.
I eventually gave up on it, used my Centris to burn some System 6.3 images and boot the Plus that way (which took like 10 times of inserting the Utilities disk, not entirely sure wth was causing that :O )
Once booted with the HD20 connected and turned on, System 6.3 recognized it, and immediately tried to mount it. It failed, and wanted me to initialize. At first I canceled, because a label that came with it claimed it had the OS and several nice apps already on the drive. I attempted to run Disk First Aid (I think) to try and solve the problem, thinking all this time in storage had simply caused some bad sectors.
Turns out that it couldn't fix whatever error was happening, so I just decided to initialize it and be done with it. This, unfortunately, also failed miserably, it won't initialize.
The controller card does seem to be fully functional though, as it does obviously spend time trying to read the disk. I thought I felt vibrations on the disk itself when I tested it earlier, so I don't know what to think.
Does anyone know of another program that may be able to get this drive working?
If the drive is indeed dead, is there any place that still services these hard drives, or would I be doomed to trying to find one on eBay D:
-Academician
The best resource I know of is http://www.mandrake.demon.co.uk/Apple/hd20.html
The site refers to a couple of utilities that might help you revive a balky HD20. I wish you success, because those drives are getting rarer all the time. My old trusty one has developed arthritis in its old age. I have to give it a little kick to get it going. Only a matter of time until that won't work...
The site refers to a couple of utilities that might help you revive a balky HD20. I wish you success, because those drives are getting rarer all the time. My old trusty one has developed arthritis in its old age. I have to give it a little kick to get it going. Only a matter of time until that won't work...
I did find the HD20 Startup Disk and burned a copy. The drive failed the test within seconds and it doesn't seem to be format-able either :'(
Thanks for the link though, it sure helped me put another nail in this things coffin so I don't have to worry about it, for a while anyway.
-Academician
Thanks for the link though, it sure helped me put another nail in this things coffin so I don't have to worry about it, for a while anyway.
-Academician
Sounds like it's gone to the great hard disk retirement home in the sky :'(
I would love the empty case if you felt you could part with it
Has anyone ever developed/discovered a replacement mechanism for this drive? I find it very hard to believe that Apple has not only a custom controller board but also a custom drive mechanism. There should be some way to fit it up with a standard RLL or MFM drive...
Hard Disk 20: Boot From HD20 Locks Up HD20 and Macintosh
PROBLEM DESCRIPTION: When trying to boot from a non-SCSI Hard Disk 20, the system fails to complete its boot.
http://docs.info.apple.com/article.html?artnum=1685
PROBLEM DESCRIPTION: When trying to boot from a non-SCSI Hard Disk 20, the system fails to complete its boot.
http://docs.info.apple.com/article.html?artnum=1685
I agree. I've been planning to open up mine "one of these days" and see what the mechanism is. As do you, I assume that the mechanism itself is a standard ST-412/506 type of drive. Still have a few of those kicking around in a box somewhere...
Academician -- if you happen to have a camera handy, could you post a few pics of the drive mechanism itself? Enquiring minds want to know...
Although I am doing quite a lot today, I'll see if I can't pry it back open later and snap a few shots.
Tom, there's no need to open your HD20. I posted a full set of photos of my HD20 here.
It's a Rodime drive mechanism. And no, I am not aware of what modern hard disk drive mechanism (if any) would be drop-in compatible for the Rodime.
And if you've not already seen my HyperDrive 20 photos on Flickr, check those out too. The drive used in the HyperDrive setup was made by a company even less well known than Rodime: Microcomputer Memories Inc. I Googled that name, but not much comes up.
It's a Rodime drive mechanism. And no, I am not aware of what modern hard disk drive mechanism (if any) would be drop-in compatible for the Rodime.
And if you've not already seen my HyperDrive 20 photos on Flickr, check those out too. The drive used in the HyperDrive setup was made by a company even less well known than Rodime: Microcomputer Memories Inc. I Googled that name, but not much comes up.
You would think. So did I... But it does not appear to be any kind of standard interface. It is possible that the wires there map to a 412/506 with some of the power or grounds removed or something, but it would be a lot of work to trace the custom controller card to the point where one could interpret the pinout of the hard drive. The connector certainly seems to be one not used elsewhere on hard drives.
Is your drive a clunker? One of my PB 150's had a clunking hard drive, which is usually a sign of a dead drive and I figured since it was already dead I had nothing to lose by opening it up and taking a look inside. Imagine my surprise when I put it back together and reinstalled it and it came back to life! I have a Western Digital drive from a beige G3 that is a clunker that I want to open up, but I don't have the right screwdriver to get it open. I'm going to see if I can eventually get that one working again if I can borrow the right tool from someone.
That's too bad, indeed. That makes resurrection of these increasingly rare drives that much less likely.
In 1984/85, Apple went to market to find an OEM to supply hard disks that would become the HD20 unit. Assume that Rodime offered a good deal for a non-standard drive, with continuity of supply, and that Apple believed that it would be cheap to build a floppy port bridge board for the offered drive. And that is what we have.
Possibly Rodime used the same drive mechanism in other offerings. I always suggest that you crack open an early compact Mac or "SCSI" drive, just to see what is inside. Rodime drives are also found in old MIDI kit too, but that kit is as scarce as an HD20.
Possibly Rodime used the same drive mechanism in other offerings. I always suggest that you crack open an early compact Mac or "SCSI" drive, just to see what is inside. Rodime drives are also found in old MIDI kit too, but that kit is as scarce as an HD20.
This is common to the HD20.
A crude way to get then going, is to open the casing, apple power, and knocking och the case until they start spinning.
This has helped me several times to get them going
/ E
A crude way to get then going, is to open the casing, apple power, and knocking och the case until they start spinning.
This has helped me several times to get them going
/ E
From JDW's pics I gather that the drive proper in the HD20 is a 3.5-in mechanism, where I might otherwise have supposed that it is a 5.25-in. The drive in his pic. closely parallels a (later?) Rodime that I have, which differs in Build Level (7A) and Option No (3), and also in logic board supply current (1.25A), which may be explained by its being patently for SCSI use. My memory is that it came from an SE/30.
Just on three years ago I received my first Apple 20SC external SCSI drive M2604, with Apple logo but no model designation (as opposed to the M2603 cases marked 20SC, 40SC, 80SC and so on). It contained a Seagate 5.25-in ST225N drive, a monster that was responsible for my paying four times the drive price in shipping cost to get it here. It may be a reasonable guess that this assembly was produced as an external drive for the Plus. Although the Plus, and the IIci also, have ROMs that can talk to an HD20, it is possible that the HD20 was quickly supplanted soon after SCSI was first built into Macs, even though Rodime continued to supply drives with SCSI controllers as internal HDDs.
de
Just on three years ago I received my first Apple 20SC external SCSI drive M2604, with Apple logo but no model designation (as opposed to the M2603 cases marked 20SC, 40SC, 80SC and so on). It contained a Seagate 5.25-in ST225N drive, a monster that was responsible for my paying four times the drive price in shipping cost to get it here. It may be a reasonable guess that this assembly was produced as an external drive for the Plus. Although the Plus, and the IIci also, have ROMs that can talk to an HD20, it is possible that the HD20 was quickly supplanted soon after SCSI was first built into Macs, even though Rodime continued to supply drives with SCSI controllers as internal HDDs.
de
Just wanted to weigh in since I didn't see this mentioned. It has always been my understanding that the Rodime drive was indeed fitted with a proprietary controller. This Apple Tech article indicates one conversion method I've heard of which seems to support that the drive itself could not be converted to SCSI, but the interface logicboard could be replaced to interpret for SCSI (or maybe I'm reading too much into it). equill's comment is equally enlightening concerning the size of the drive itself. Clearly the case was designed to accommodate a 5.25" drive. When I first cracked my HD-20 case I was in awe at all the wasted space. Indeed if you look at JDW's pictures you'll see what I mean. From an aesthetic perspective I always hated the bulge on the back to accommodate the fan. This could be the result of a last minute change from the 5.25 they were planning to, as Charlieman suggests, a deal with Rodime to provide the smaller 3.5" drive for eventual inclusion in other Macs. With the 3.5" drive the fan could have easily been included within the footprint of the Mac.
As for a dead unit, assuming it's not the drive itself, you could always hold out for one of these SCSI conversion kits mentioned in the Apple article, but that may be just as rare as a replacement HD20 drive if that's your problem. Otherwise you could replace the whole shebang with a modern internal SCSI drive. I have thoughts of putting my ZIP 100 in there since it will boot with system 1.0 through 6 (once formatted) and is absolutely silent when not accessing the disk and requires no fan. 100MB is plenty with an old Mac (and significantly more than the HD20). Disk access would have to be through a modified hole in the side vents, but that would be a minor alteration, mostly hidden by the external disk drive, which by the way the ZIP would easily fit inside as well, though requiring more visible cosmetic surgery on an already rare and useful 400K drive enclosure.
It could even be used with a 512k and possibly a 128K Mac with 128K ROMs and a Dove MacSnap SCSI card which surfaces on eBay from time-to-time (albeit not cheap!) Seethis Apple article. Using something like MacServe you could even format an MFS volume partition comprising almost the entire volume and still avoid switching to HFS.
Even if I had a working HD20, I'm not sure I would use it except for storage (the main reason I want a viable 800K MFS drive solution) to be accessed at a minimum. It is a noisy beast that must have driven Steve Jobs out of his mind ... oh yeah, he left Apple the month it was released! LOL
As for a dead unit, assuming it's not the drive itself, you could always hold out for one of these SCSI conversion kits mentioned in the Apple article, but that may be just as rare as a replacement HD20 drive if that's your problem. Otherwise you could replace the whole shebang with a modern internal SCSI drive. I have thoughts of putting my ZIP 100 in there since it will boot with system 1.0 through 6 (once formatted) and is absolutely silent when not accessing the disk and requires no fan. 100MB is plenty with an old Mac (and significantly more than the HD20). Disk access would have to be through a modified hole in the side vents, but that would be a minor alteration, mostly hidden by the external disk drive, which by the way the ZIP would easily fit inside as well, though requiring more visible cosmetic surgery on an already rare and useful 400K drive enclosure.
It could even be used with a 512k and possibly a 128K Mac with 128K ROMs and a Dove MacSnap SCSI card which surfaces on eBay from time-to-time (albeit not cheap!) Seethis Apple article. Using something like MacServe you could even format an MFS volume partition comprising almost the entire volume and still avoid switching to HFS.
Even if I had a working HD20, I'm not sure I would use it except for storage (the main reason I want a viable 800K MFS drive solution) to be accessed at a minimum. It is a noisy beast that must have driven Steve Jobs out of his mind ... oh yeah, he left Apple the month it was released! LOL
A kindred spirit. Despite it being out of view (in the back, as opposed to the front), I know "the fan bulge" is there, and for some reason it bothers me.
The Japanese contend that such feelings are characterstic of those, like me, who have Type-A blood. :b&w:
I should worry a lot more if I were to discover that they esteem some culinary delicacy made from Type A blood.
de
de
What I find particularly interesting about this article, is that it implies that, at one time, someone at PCPC understood the interface to the HD20 drive--either that or this adapter sits between the floppy connector and the host computer, but I do not think that is the case. I think it is a replacement interface board, from the way the article is worded.
So, we must now find someone who did design work for PCPC...
I saw (but did not bid on) one of these interface kits on eBay not long ago. The listing appears to have dropped off the completed search.
From what I recall, it appeared to replace the logic board in a HD20 to provide a SCSI interface to the HD20 drive mechanism.
Regards,
Macdownunder
While it is perfectly conceivable that Rodime might have used different platter separations and different head constructions in the same motor-and-platter diecast box as they later used for SCSI drives, providing a different logic board also for each style of storage, it seems a little painful. JDW's pics of the Rodime in his HD20, and my SCSI drive, differ only in 'Option Number' (read construction/storage mode?) and Build Level (que?), nonetheless.
I have to presume that Rodime never 'filed' its secrets on the Web?
de
I have to presume that Rodime never 'filed' its secrets on the Web?
de
That's how I read the Apple article, too. While I am the last person to discuss technical matters of this nature, if equill's drive is physically identical to the HD20 drive mechanism, I would suggest that the circuit board interface on the drive is the difference and is designed to interface with Apple's HD20 digital board which is sending very different signals than a SCSI interface. I suspect any conversion kit not only provided access to the Mac's's SCSI bus but also translated those signals to the proprietary hard drive controller. So theoretically you could just trade disk controllers for a native SCSI and be all set to plug into a SCSI interface. However, that doesn't really get you any closer to converting the HD20 to SCSI without a SCSI logic board. In other words, strip the guts out of the HD20 reusing only the hard disk and power supply but replacing all logic circuitry. In which case why even keep the drive itself? And the power supply would have to be adjusted to the needs of the new mechanism.
I have found this thread to be quite interesting, especially the technical points hinting at the HD20's interface and protocol. But for myself, I am even more interested in figuring out how to put a bootable flash drive inside my old non-SCSI Mac 512k! Or perhaps substituting a 20MB or 32MB CF flash card for the Rodime drive mechanism in the HD20! Or perhaps swapping the MMi drive mechanism used in the HyperDrive kit with a 20MB CF card! Or for those without either the HD20 or the Hyperdrive, having a CF card and controller kit to be used internally in the Mac 512k and higher (and 128k too, if it has the RAM for it).
Flash drive options exist for the ancient Apple II series, as I am sure most of you have seen on EBAY from time to time. So why not the Mac? Makes no sense to me as we Mac collectors should also have an equally interesting number of modern add-ons for our old machines! But then, perhaps this is a topic for another thread.
Flash drive options exist for the ancient Apple II series, as I am sure most of you have seen on EBAY from time to time. So why not the Mac? Makes no sense to me as we Mac collectors should also have an equally interesting number of modern add-ons for our old machines! But then, perhaps this is a topic for another thread.
While it would be a dream, as Dan Knight points out, someone would would need to write drivers for it and I'm afraid anything less than a System 6 would not get much attention.
http://lowendmac.com/musings/mm07/0815.html
However, I have routinely used IDE to SCSI converters so I could use smaller IDE, cheaper drives on an old SCSI internal bus. Since there are ATA/IDE Flash drive interfaces, this may well be a solution with the right connectors. No special drivers, just connect your flash drive through the IDE to SCSI adapter and plug into your SCSI bus. Depending on the flash drive you may need a special application to format it before you can see it on a very old System (like a ZIP 100 drive), but once formatted it might work on any old System just like my ZIP does.
I'm thinking the better approach at this point would be the MacMinitosh running Mini vMac and expand its capabilities ... which I know Paul Pratt is doing. This way you can have the best of both worlds in one case (I think I would mount my MacMini upside down and access the DVD slot through the bottom side vents to modify the case as little as possible.
But, you're right this belongs in it's own topic ...
http://lowendmac.com/musings/mm07/0815.html
However, I have routinely used IDE to SCSI converters so I could use smaller IDE, cheaper drives on an old SCSI internal bus. Since there are ATA/IDE Flash drive interfaces, this may well be a solution with the right connectors. No special drivers, just connect your flash drive through the IDE to SCSI adapter and plug into your SCSI bus. Depending on the flash drive you may need a special application to format it before you can see it on a very old System (like a ZIP 100 drive), but once formatted it might work on any old System just like my ZIP does.
I'm thinking the better approach at this point would be the MacMinitosh running Mini vMac and expand its capabilities ... which I know Paul Pratt is doing. This way you can have the best of both worlds in one case (I think I would mount my MacMini upside down and access the DVD slot through the bottom side vents to modify the case as little as possible.
But, you're right this belongs in it's own topic ...
Interesting solution.
Can't figure out if he's talking about an HD20, an HD20 SC or a third party drive. Either way, the Rodime mechanism looks awfully familiar!
http://www.bernardbelanger.com/computing/hd/index.html
Can't figure out if he's talking about an HD20, an HD20 SC or a third party drive. Either way, the Rodime mechanism looks awfully familiar!
http://www.bernardbelanger.com/computing/hd/index.html
Mac128 (love your new Avatar BTW),
You Google-up the most interesting classic Mac links on the web! That drive indeed looks to be the same as the drive mechanism inside my HD20. I just never opened the housing to see the heads move.
Thanks for bring this to our attention.
You Google-up the most interesting classic Mac links on the web! That drive indeed looks to be the same as the drive mechanism inside my HD20. I just never opened the housing to see the heads move.
Thanks for bring this to our attention.
Quote from the page: "This one is an old one, a 20 MB Rodime that came with a Mac Plus." Presumably the drive came in a third party external SCSI enclosure (Rodime drivers were very common in Europe and I've got loads).
Anybody on the forum with an HD20 got the original manual or a copy of one?
The Service Source for the Hard Disk 20 was, before Apple's counsel assiduously shut them down, available from a number of sites. If you find one that they have missed, don't post its URL.
As far as I am aware, the hard-copy manual 030-1228-A has not been downloadable from Apple at all.
de
As far as I am aware, the hard-copy manual 030-1228-A has not been downloadable from Apple at all.
de
But be sure to PM me! :b&w:
I've just dug out my copy. The media kit comprises the HD20 Manual (030-1228-A), an addendum (032-0026) and startup disk (690-5067-A). Those documents don't cover anything that I haven't written up already at http://www.vintagemacworld.com/hd20.html
There is some additional information in the service procedures -- I have a paper copy from 1989 that includes a diagnostics section for the HD20 dated November 1986:
-- Only use a Plus or earlier to try to fix an HD20. Don't use an SE or II.
-- Boot from the HD20 Startup Diskette and hold down the Command and Option keys through the entire boot process to rebuild the desktop.
-- Boot from the HD20 Startup Diskette and hold down the Command, Option and tab keys through the entire boot process to initialise the HD20.
I haven't tried the third procedure and would be interested to hear if it is different from the optional procedures available in "HD 20 Test".
For info, the paper doc is "Apple Service Technical Procedures, Macintosh Family, Volume Two" (072-0228). The doc covers peripherals, monitors and cards for early Macs upto and including Mac II. Volume One (same part number) covers the Mac 128 through to IIcx system boxes.
LOL, yes Phil, you indeed comprise all the current comprehensive information to be found on the net! I might have known you had the original manuals. Would love to get my hands on a PDF of the manual though ... mainly to read how Apple explained the HFS format and instructed the new adopters to implement it. As you well know, Apple quietly introduced it with the HD20 in September 85 when no one would have known anything about HFS and would have resulted in a lot of confusion unless it was clearly explained. Though as you say, the manuals don't cover anything you haven't written up. The disk part number looks as though it may be the original 2.1/5.0 v1.0 as well. Thanks for digging around to assist with this!
I don't have the time to do the scanning to create a PDF. Drop me a line privately, David, and I'll investigate whether I can produce high quality photocopies to post to you. I'm not sure about hosting -- I'll have a chat to some of the people who have reproduced Apple II stuff to see if Apple generate any legal problems.
If someone who has these wants to ship them to me (in Japan), I will MAKE THE TIME to scan them for everyone to have access to. (And there's no reason bitmap scans really need to be in PDF format. Since there's no vector text in such scans, even JPEG format will do.)
FYI, I have the HyperCard stack of the HD20 service source manual and trust me when I say it doesn't offer any revelations other than preventing you from breaking the clips when you open the case. It's from a time when Apple's answer even to their field techs was "return to Apple for repair". Anybody who wants a copy just PM me.
I too have finally been able to diagnose my dead HD20 and it appears to be a dead drive. The logic board powers a replacement drive just fine. This is most likely the case with yours Academician since mine exhibited all the same symptoms as yours.
I did open the HD itself and the platters and the internals all seem to be in working order. So if nothing physically is damaged, then does the problem lie on the drive's circuit-board? I haven't a clue as to where to start looking, if so.
It is sad to think that as these drives fail there is no good way to replace them. In fact I find it almost unbelievable there is no modern way to replace the drives, even with some sort of homemade adapter. Well, here's hoping.
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. In which case, it should be possible to adapt any SCSI drive to work with the HD20. Anyone with a 20MB drive from one of those Macs should check the part number and see if it may be a compatible drive with the HD20, since you can switch out your SCSI HD with any old SCSI drive, but the HD20 can evidently only use one.
FYI, Service Source indicates of the two Revisions of the 20MB hard drive the 661-0373 is the only one that is drop-in replacement. In other words all other drives require the techs to insert/remove them from their carrier/sleds and configure the dip switches, terminator resistors, etc. for the specific enclosure, but the 661-0373 is pre-configured by Apple
I too have finally been able to diagnose my dead HD20 and it appears to be a dead drive. The logic board powers a replacement drive just fine. This is most likely the case with yours Academician since mine exhibited all the same symptoms as yours.
I did open the HD itself and the platters and the internals all seem to be in working order. So if nothing physically is damaged, then does the problem lie on the drive's circuit-board? I haven't a clue as to where to start looking, if so.
It is sad to think that as these drives fail there is no good way to replace them. In fact I find it almost unbelievable there is no modern way to replace the drives, even with some sort of homemade adapter. Well, here's hoping.
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. In which case, it should be possible to adapt any SCSI drive to work with the HD20. Anyone with a 20MB drive from one of those Macs should check the part number and see if it may be a compatible drive with the HD20, since you can switch out your SCSI HD with any old SCSI drive, but the HD20 can evidently only use one.
FYI, Service Source indicates of the two Revisions of the 20MB hard drive the 661-0373 is the only one that is drop-in replacement. In other words all other drives require the techs to insert/remove them from their carrier/sleds and configure the dip switches, terminator resistors, etc. for the specific enclosure, but the 661-0373 is pre-configured by Apple
If it were me, I'd strip a crappy external scsi and stick in that case.
Or try and stick and LC mobo or something else neat inside. I would spend all of 40 seconds trying to save a 20MB HD that is just as fast as a floppy. Unless of course a client was paying me large piles of cash (say a couple hundred bucks) to save. Then I would use every trick in the book and even come up with some new ones.
Or try and stick and LC mobo or something else neat inside. I would spend all of 40 seconds trying to save a 20MB HD that is just as fast as a floppy. Unless of course a client was paying me large piles of cash (say a couple hundred bucks) to save. Then I would use every trick in the book and even come up with some new ones.
Hahaha. It sounds like something I would do. I have a Rodime too (only the case remains), and a GCC HD20 Hyperdrive. Nice cases.
Some later cases, notably the Micronet ones and Mass Micro ones now have IDE drives with either USB or SCSI bridges depending on their use.
Some later cases, notably the Micronet ones and Mass Micro ones now have IDE drives with either USB or SCSI bridges depending on their use.
The whole reason we are trying to save these drives is because they are the only ones that will work with a stock 512K/e which are still around. It also has to do with something many of us on these forums are committed to, preserving these artifacts in their original condition.
Besides, I had already suggested using my Zip 100 drive in the case, assuming the drive were completely beyond repair. The one problem with that idea is neither the 512K or 512Ke are SCSI capable. The only way to add that functionality is modify the logic board and case, which sort of defeats the point of restoring these Macs to their original condition and preserving them.
I know JDW made himself clear on the oddball 128K mourning thread about the "stock" differences between his SE and 512K, but unlike the SE, despite the fact Apple did not build into the Macintosh any expansion capabilities, many third parties provided some excellent products to add these capabilities. Though Apple did not support them directly, the fact that references to many can be found in Apple's Knowledgebase is sort of a tacit approval on their part. With that in mind, like others on the forum, I think anything that can be added to a vintage Mac that is non-destructive preserves it in its original condition as it might have existed at the time. In the case of the Dove MacSnap SCSI upgrade, it actually takes advantage of the one feature of the Mac that Apple did design to be upgraded: the ROMs. The only socketed chip on the logic board. That my friends is the original Macintosh expansion slot! Pull the ROMs, insert the board and re-install the ROMs. Instant SCSI, the port for which cleverly takes the place of the battery cover on the rear. It does require 128K ROM upgrade, but again, the Macintosh was designed for that. Depending on when you bought your 512K, it may well have been an option you had installed upon purchase like you might extra RAM or bigger hard drive today.
There were other solutions which clipped onto the CPU and RAM which were also non-destructive solutions. Though as Larry Pina points out, any additional power consumption to the already overtaxed Mac must be compensated for or risk major component failure AND that really defeats the goal of preserving these old Macs!
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.
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.
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.
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.
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 ...
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 ...
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.
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.
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.
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 !
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 !
Wow..got some pics of this board? :O
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!
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!
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...
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...
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
>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
About :
Here are some inside pictures of my SC20 :
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.
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.
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.
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!
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!
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!
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)!
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?
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.
Hey guys...
Pics of my HD20 SCSI conversion board
I heard this is pretty rare !
Pics of my HD20 SCSI conversion board
I heard this is pretty rare !
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?
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?
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...
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...
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?
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?
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.
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.
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.
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.
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.
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
* 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
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.
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?
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?
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.
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.
The cable is exactly like this.
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?
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).
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).
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?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
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.
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.
Horrible, horrible things. MUAHAHAHAHAHAHA!!!
I'm looking for an aesthetically appropriate external expansion box for an SE/30 project machine.
If you still have the HD20, would you like to sell the case?