IIe drive in a IIc

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IIe drive in a IIc

Hey everyone!

Wow, it's been quite a while since I was here!  Hope everyone is OK, survived COVID as well as one could hope, and still enjoying the hobby!

So I have a IIc that I have taken out of the battered IIc case and would like it to run a longer disk drive cable.  I believe that a Disk II cable will work, and it certainly seems to work just fine.  However, the Disk II ALSO works (not just the IIc drive), which I found fascinating, though that is likely old news to you pros.  :)

One thing, though.  The Disk II will boot to DOS 3.3, etc. but when the drive is NOT in use, the IIc's disk use  red light stays on.  This is strange, to my mind.  It is not the cable, as the IIc drive works just fine with it, and the disk use light stays off when the drive is not being accessed.

Anyone know why this would happen?

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One thing, though.  The Disk

One thing, though.  The Disk II will boot to DOS 3.3, etc. but when the drive is NOT in use, the IIc's disk use  red light stays on.  This is strange, to my mind.  It is not the cable, as the IIc drive works just fine with it, and the disk use light stays off when the drive is not being accessed.

Anyone know why this would happen?

The activity light comes on because the Disk II internally draws 12-volt power from pins 13, 15, 17, and 19, but the Apple //c motherboard only supplies 12-volt power on pins 13, 15, and 17.  Pin 19 was reassigned to a TTL signal (DISK*) on the Apple //c, but the Disk II connects pin 19 to the other 12-volt power pins.

Consequently, atttaching a Disk II to an Apple //c motherboard will feed 12-volts back through the DISK* activity signal unless you disconnect pin 19 in the cable.

So attaching a Disk II directly to an Apple //c through an ordinary cable can damage or destroy these components on the Apple //c motherboard:

  • the activity LED
  • the IWM at position UD2
  • and the PAL at position UD6.  

Replacements are not readibly available for the IWM and PAL, so it's unwise to attach a Disk II directly to an Apple //c unless you make a custom cable to isolate pin 19.

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Yikes!  Thanks for that

Yikes!  Thanks for that information!

Guess I had better not do that anymore, then.  I will stick with the IIc drive, I don't particularly want to fry the IIc itself!

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S.Elliott wrote:...reassigned
S.Elliott wrote:
...reassigned to a TTL signal (DISK*) on the Apple //c

 Pin 19 of the Internal disk drive connector is actually called DISKACTY and ONLY connects to the Drive LED on the keyboard. So there's no real harm in connecting a DISK II drive there. No danger to the IWM or PAL.

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jeffmazur wrote:S.Elliott
jeffmazur wrote:
S.Elliott wrote:
...reassigned to a TTL signal (DISK*) on the Apple //c

 Pin 19 of the Internal disk drive connector is actually called DISKACTY and ONLY connects to the Drive LED on the keyboard. So there's no real harm in connecting a DISK II drive there. No danger to the IWM or PAL.

Good point, DISK* vs DISKACTY.

I was referring to an Apple //c schematic in Apple Thesaurus, which is just legible enough to guess what it says...but just blurry enough to guess wrongly.

In September someone suggested elsewhere on the forum that the IWM could be fried by connecting a standard Disk II to the Apple //c internal IDC20 socket.

With that in mind, it sure looked like trouble the diagram that showed pin 19 (DISKACTY) on the Apple //c motherboard connects to pin 19 (+12 volts) on the Disk II.

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Hey, thanks, fellows!  I

Hey, thanks, fellows!  I appreciate the update, and glad to hear I didn't almost cook my IIc!  =)

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