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IIgs no longer seeing 3.5 drives. Bad VGC?


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I have an Apple IIgs that has been working just fine. But a little while ago, I find that 3.5" drives are no longer recognized.  The computer still works with 5.25" drives, which seems to indicate the IWM is still functional.  I asked the question on an Apple II forum, and someone suggested it's likely a bad VGC chip.  I found the schematics for the IIgs, and tested the traces from the VGC to the floppy port, and I have good connectivity with proper resistance on both lines (pins 51 and 61).  But I do not know the logic of how the HDSEL and and 3.5DISK lines work to test the output with my scope.  Any suggestions?

 

Also, does anyone have a spare 344S0046-C or a battery-eaten IIgs motherboard with a likely good chip (soldered version)?

 

 

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I mean... I don't... but when you say doesn't recognize, do you mean it doesn't appear to read them on boot or it doesn't recognize in some system (I'm thinking specifically GSOS where you might have to expressly install the drivers).  [And I don't think DOS 3.3, to continue this line, can read 3.5" disks at all.]

Edited by raoulduke
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It doesn't see them on boot.  Instead of the normal search for media, the drive indicator gets a very, very quick flash with no spin up.  (Normally, the LED stays on for about a second and you can hear the head click a few times)  I've tried multiple bootable PRODOS game disks, and GSOS. The eject function still works, but thats it. I've tried both drives independently with the same result.  Both drives work fine when connected to a Mac, and like I said before, the 5.25" disk works if I connect that.

Edited by joethezombie
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eh... http://apple2.org.za/gswv/a2zine/faqs/Csa2FDRIVE.html#009

 

well wait i mean i can't really picture what you're saying about boot but i assume you mean that it doesn't seem to be scanning the drives normally.  i can't imagine that link will help but does anything in that seem ballpark?  also not a control panels issue?  i was thinking maybe you changed your boot settings, but i'm not sure about the interaction with the 5.25" drive.

Edited by raoulduke
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Both drives work fine when connected to a Mac, and like I said before, the 5.25" disk works if I connect that.

 

Ewww... Big Ewww...!!!

 

Apple IIGS Drives are not Mac Compatible, and plugging them into a Mac will burn something out in them. If you did this before, and you put the dries back into the IIGS. then you burnt something out in them.

 

Apple 3.5 drives and Mac 3.5 drives are mechanically compatible but not electronically compatible. You are very luck you did not burn out your SIWM Chip on the Mac! (Unless you did and you do not know about it... yet.) And blown Apple IIGS Drives also erases Boot Floppy Disk in a similar way that Mac blown drives do.

 

Time to get another Apple 3.5 drive and try it on the IIGS WITHOUT A FLOPPY DISK and see if the SIWM Chip picks it up normally. Let it Bonk into an error before putting in a Boot disk. Then reset the machine with option-apple-reset. If you did not erased your disk, it should boot.

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Beginning in September 1986, Apple adopted a unified cross-platform product strategy essentially eliminating platform specific peripherals where possible. The Apple 3.5" Drive (A9M0106), is an 800K external drive released in unison with the Apple IIGS computer, and replaced the beige-colored Macintosh 800K External Drive. It works on both the Apple IIGS as well as the Macintosh.

 

 

It's the 5.25" drives that will kill a Mac.  The A9M0106 is fully compatible.

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No one here has to believe what I post abut Apple 3.5in disks on a Mac. That is up to you. What I post is from experience having seen it happened with friends and schools I worked for and tried to repair them.

 

It is my experience if you put an Apple 3.5in Floppy Drive into a Mac, you will blow out that drive. You can put that drive in question on any other Apple with a 3.5in interface and it will not work on any of them. Only test you can do is to get a good working 3.5in Apple Drive to test on your IIgs, if the bad drive did not blow out your IIgs' disk interface.

 

Again, you do not have to listen to me on this, but if you continue putting Apple 3.5in disk drives into Macs, it is going to get expensive after a while. How much does a Apple 3.5in drive go for these days? Compared to a Mac's 3.5in drive?

Note: if you would have taken a Apple 3.5in 800K drive apart along with a Mac 3.5in 800K drive and compared them, you would see that there are extra electronics in the Apple unit while the Mac one is directly wired to the cable. It is this extra electronics you blew out by plugging into a Mac. Now if you can get a replacement board or chips for the board, then maybe you can fix it.

 

Rant: Then again, who am I to make such statements for you to believe in? My Apple/Mac experience goes back further than some forum members have been alive, but who cares. Right? Continue to plug in 800K 3.5in Apple drives into Macs, maybe you will learn something after blowing out the 10th one.

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If A9M0106 drives self destruct when using with a Mac, why did Apple brand, advertise, and sell the drives for Mac use?  Or are you suggesting Apple sold (for years) drives that would damage equipment when used for the intended purpose?  Perhaps the drive you are speaking of is a different model such as the UniDisk 3.5 (a2m2053) which looks similar but isn't compatible?

 

More than likely, I have found the culprit of my problem.  Under interrogation, my son has admitted to pulling the drive "live" and attaching the FloppyEmu.  I have a replacement mainboard on the way, but in the interim, both drives still work great on my Macs.

 

 

 

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No one here has to believe what I post abut Apple 3.5in disks on a Mac. That is up to you. What I post is from experience having seen it happened with friends and schools I worked for and tried to repair them.

 

The reason no one believes you is because according to Apple's own documentation you are *wrong*, the A9M0106 was sold by Apple as a universal drive. Here are some supporting documents:

 

Apple Service Source:

 

https://archive.org/details/Service_Source_Apple_3.5_Drive

 

"Apple 3.5 Drive Technical Procedures":

 

https://archive.org/details/Apple_3.5_Drive_Technical_Procedures

 

Owners Manual:

 

https://archive.org/details/Apple_3.5_Disk_Drive_Owners_Guide_alt

 

Need I go on?

 

Interestingly enough, according to the "Technical Procedures" document there *is* a flaw in the Rev. A version of the daisy chain board that can cause it to malfunction due to static buildup, but that has *nothing* to do whatsoever with whether you plugged it into a Mac or not.

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I'm not stating what is being stated by Apple is or is not correct.

 

I am stating that by my experience and memory - point 1, point 2, point 3...

 

My experience and memory with the Apple 3.5in drive is that when you plug into a Mac, you blow it out. Whether or not you are blowing out this Daisy Chain board or other damage is done remains to be seen; I remember that tiny circuit board in the back of the Apple drive going bad after plugging it into a Mac and this goes back to the 1990s with the NYC Big Apple User's group (BAUG). Whether the damage done extends to the computer with its onboard chip going too remains to be seen as it depends on how long you keep it turned on.

 

Furthermore, this is the 4th or 5th thread posting on this forum of "My Apple IIgs 800K Drive is dead after plugging into a Mac!" And there are many many more on the web. Don't you see a pattern here?

 

Once - It's an accident.

Twice - It's a Coincidence.

Three Times - It's a Conspiracy.

Four Times? It's a sure thing.

 

Now, I've been reading up to catch up on this...

 

There are two so-called Apple II 3.5 in 800K drives - the longer produced UniDrive and the Apple 3.5in drive. The cases on both are almost identical. The problem as I see it happens on the UniDrive as there is a problem with that drive being plugged into a Mac.

 

So what drive was plugged into the Mac and got blown out? Don't tell me that its an Apple 3.5in 800K drive. Chances are it is a Unidrive that is being plugged in and getting blown out. Remember they almost look identical. I'm seeing this:

 

An Apple II user has this:

https://en.wikipedia.org/wiki/Macintosh_External_Disk_Drive#Apple_UniDisk_3.5

 

but reads this (the Apple Notes as well):

https://en.wikipedia.org/wiki/Macintosh_External_Disk_Drive#Apple_3.5.22_Drive

 

and thinks they own the second drive and not the first. And thus in reading that it can be plugged into a Mac, they plug it in and blow it out. Then they sit there and wonder why it does not work after that.

 

The only way to be sure is to open the drive case up and look at the electronics inside. If the cable plugs directly to the floppy drive then its the second Apple 800K Drive. If the cable goes to a small controller board inside the the drive before going to the floppy drive, then it is the UniDisk that can not be plugged into a Mac. Doing so will blow it out.

 

Who's fault is this? The User? Apple's because they said that it can be done and not clarifying labels and making nearly identical external cases?

 

Since I seen this happen so many times, I push the notion of "Never Plug in an Apple 3.5in Drive into a Mac or you will blow it out!" This insures that another Apple 3.5in (Unidisk or not) does not get blown out. But because this is happening so many times again and again, it is getting expensive. But the logic for safety sake is simple - If it says "Apple", it goes with the Apple IIs. If it says "Macintosh" it does with Macs. And may the two never mix.

Edited by Elfen
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So:

 

So what drive was plugged into the Mac and got blown out? Don't tell me that its an Apple 3.5in 800K drive. Chances are it is a Unidrive that is being plugged in and getting blown out. Remember they almost look identical. I'm seeing this:

 

This argument isn't about whether it's okay to plug a Unidisk into a Mac or not. (It's not.) It's also not about whether Apple was acting intelligently or profoundly stupidly when they used the same 19 pin connector for Mac floppy drives as Apple II drives when plugging the vast majority of Apple II compativle drives into a Mac will either do nothing useful or damage one piece of equipment or another.  This is about you yelling at someone who *KNOWS* what drive they have in their possession and knows damn well that it's compatible with both machines that they should never connect it to a Mac because "Apple IIGS Drives are not Mac Compatible". On this point you are flatly *wrong*, period, full stop. To continue:

 

 

Since I seen this happen so many times, I push the notion of "Never Plug in an Apple 3.5in Drive into a Mac or you will blow it out!" This insures that another Apple 3.5in (Unidisk or not) does not get blown out. But because this is happening so many times again and again, it is getting expensive. But the logic for safety sake is simple - If it says "Apple", it goes with the Apple IIs. If it says "Macintosh" it does with Macs. And may the two never mix.

 

Apple sold two models of Macintosh-only floppy drives, the original 400k External M0130 and the 800k M0131. (And, yes, they sold the Apple II-only Unidisk.) HOWEVER, when the Apple IIgs was introduced they discontinued the M0131, leaving the A9M0106 as the *only* external floppy drive solution for either sort of system, at least until the identically styled 1.44MB G7287 came out. (Which, notably, is also compatible with the IIgs, although it will just be usable as an 800k drive unless a special controller card is fitted.) In other words, after late 1986 there *WERE* no floppy drives that just said "Macintosh" on them. Period. Full stop. Every external Apple 3.5" disk drive sold from before the debut of the Macintosh SE up until they stopped selling them period is off limits according to your advice because they *could* be confused for the Unidisk. (Even though the Unidisk *does* have some significant styling differences that should make it not *that* hard to explain the difference to someone if they bother to ask if it's compatible before plugging it in, rather than just looking at the 19 pins on the cable and just jumping to conclusions.) Yeah, that's totally reasonable.
 

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The M0131 lacks the daisy chain board's logic for drive selection, so it won't work on a IIgs. The FloppyEmu had the same problem until the universal adapter board was created. The A9M0106 Apple 3.5" Drive was specifically designed to be a universal drive. The design documents make note of the different flavors of DB-19 pin outs and addressed the electrical differences in the various machines using the daisy chain board. The "A9" prefix was designated by Apple for "family peripherals" that worked on both Macintosh and Apple II machines. I have connected my A9M0106 that came with my IIgs to a Mac 512k, Mac SE, and Macintosh Portable without a problem.

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So my replacement "dead" mainboard arrived today.  I was going to use its VGC chip first, and failing that, try its IWM.  But looking at the "dead" board, it looked mighty nice, so I decided to try and boot it.  Imagine my surprise when the "dead" replacement board I bought for $15 came right up!  And it's a ROM3 board at that!  Diagnostics check out, everything works,!  Happy me!  :b&w:

 

I still want to fix my original mainboard, so I guess I'll go looking for parts again.

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  • 4 years later...

Replying to a 4-year-old thread for documentation purposes, in case somebody else has the same problem in the future. For the IIGS to communicate with a A9M0106 Apple 3.5" Drive, or any compatible "dumb" 3.5 inch floppy drive, the disk I/O signals HDSEL and EN35 must both be working. Both of these signals come from the VGC chip, not the IWM chip like the other disk signals do. And neither of these signals is used for communication with 5.25 inch drives or Smartport/Unidisk drives. So if your IIGS suddenly won't work with 3.5 inch drives, but works fine with other drives, you probably have a bad VGC.

 

There's something very strange about both the HDSEL and EN35 signals: they both can potentially be short-circuited by a connected drive. EN35 is an output from the IIGS, but if you connect a 5.25 inch floppy drive, that pin is connected to ground inside the drive. HDSEL is also an output from the IIGS, but if you connect an intelligent drive like the Unidisk 3.5, that pin is connected to ground inside the drive. Either scenario would create a potential short-circuit between a VGC output and GND. Apple guards against this by putting a 470 ohm inline resistor in the path of each signal on the IIGS motherboard. You can see this on page 4 of the IIGS schematics. Note that EN35 is called 3.5DIK on the schematics.

 

The resistors limit the short circuit current to about 10 mA. Presumably that's a safe level of current for the VGC. So why are some people seeing this kind of VGC-related 3.5 inch drive failure? I've tried to help a couple of people troubleshoot this in the past few years, but I don't have an answer. Maybe 10 mA is a safe current level for a newly-made VGC, but a 30-year-old chip will have degraded silicon and 10 mA continuous current will eventually burn out the drivers for those pins?

 

@joethezombie if you still have that busted IIGS motherboard, and an oscilloscope or logic analyzer, I'd be curious to know what you see on HDSEL and EN35. You can measure the direct outputs from the VGC on the motherboard at test point TP153 (HDSEL) and TP111 (EN35). You can measure the voltage after the protection resistor at the external disk port, on pin 16 (HDSEL) and 4 (EN35). During disk activity with a 3.5 inch drive, you should see both signals switching high and low.

 

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  • 4 weeks later...
On 12/15/2020 at 5:07 PM, bigmessowires said:

Replying to a 4-year-old thread for documentation purposes, in case somebody else has the same problem in the future. For the IIGS to communicate with a A9M0106 Apple 3.5" Drive, or any compatible "dumb" 3.5 inch floppy drive, the disk I/O signals HDSEL and EN35 must both be working. Both of these signals come from the VGC chip, not the IWM chip like the other disk signals do. And neither of these signals is used for communication with 5.25 inch drives or Smartport/Unidisk drives. So if your IIGS suddenly won't work with 3.5 inch drives, but works fine with other drives, you probably have a bad VGC.

 

There's something very strange about both the HDSEL and EN35 signals: they both can potentially be short-circuited by a connected drive. EN35 is an output from the IIGS, but if you connect a 5.25 inch floppy drive, that pin is connected to ground inside the drive. HDSEL is also an output from the IIGS, but if you connect an intelligent drive like the Unidisk 3.5, that pin is connected to ground inside the drive. Either scenario would create a potential short-circuit between a VGC output and GND. Apple guards against this by putting a 470 ohm inline resistor in the path of each signal on the IIGS motherboard. You can see this on page 4 of the IIGS schematics. Note that EN35 is called 3.5DIK on the schematics.

 

The resistors limit the short circuit current to about 10 mA. Presumably that's a safe level of current for the VGC. So why are some people seeing this kind of VGC-related 3.5 inch drive failure? I've tried to help a couple of people troubleshoot this in the past few years, but I don't have an answer. Maybe 10 mA is a safe current level for a newly-made VGC, but a 30-year-old chip will have degraded silicon and 10 mA continuous current will eventually burn out the drivers for those pins?

 

@joethezombie if you still have that busted IIGS motherboard, and an oscilloscope or logic analyzer, I'd be curious to know what you see on HDSEL and EN35. You can measure the direct outputs from the VGC on the motherboard at test point TP153 (HDSEL) and TP111 (EN35). You can measure the voltage after the protection resistor at the external disk port, on pin 16 (HDSEL) and 4 (EN35). During disk activity with a 3.5 inch drive, you should see both signals switching high and low.

 

 

@bigmessowires, I recently purchased a ROM01 IIGS and I'm seeing this exact problem. I have an Apple 3.5" drive, a Disk IIc 5.25" drive, and one of your excellent floppy emulators. The system reads 5.25" physical disks and images from the emulator, but neither the 3.5" drive nor the emulator in 3.5 mode work. The system won't boot/read from anything off of Slot 5, it appears. I do have an oscilloscope (Siglent SDS1202X-E), so I'd be happy to try to investigate this with you. I may need a little coaching, but I think I have the equipment that will be needed. I don't have access to any other IIGS machines, so I won't be able to try a replacement VGC yet.
 

Edited by RPGCoder
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Well for anyone interested I looked in my A9M0106 manual and found this, so I think this speaks for itself in regards to using the A9M0106. You can see the manual says for IIGs and MAcintosh, and the pages inside tell you which mackintosh models exactly. I have no idea why the pictures are sideways, They arent this way on my computer and I cant find a way on this forum to change the orientation.

20210114_140037.thumb.jpg.79285d182361a1eb7d98eabda212f8ca.jpg

20210114_140044.jpg

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