IIc Disk Drive/IWM problems

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Joined: Jul 28 2016
Posts: 2

Hey guys,

I’ve been trying to fix this problem for over a week, and I cannot find a solution. I've been told that you guys know these things inside and out so I was hoping you could help me. I absent-mindedly tried plugging an external drive to my IIc while it was on and running (more details here), and now the drives won’t read or write. Here are the facts:

  • The computer runs entirely fine, except for disk things. I can use the monitor, BASIC, and bootstrap ADTpro and they all work fine.
  • When trying to read, the head twitches back and forth very quickly (making the signature clicking noise), but it doesn’t move to the beginning as I believe it’s supposed to (this goes for both drives)
  • I’ve tried both drives in both bays and vice versa, which leads me to believe that the problem is possibly on the main board and not with the drives
  • I probed the IWM with a voltmeter (I won’t have access to an oscilloscope until after I go back to school), and at startup pins 2, 27, and 28 all toggle on and off while pin 1 does not (these pins are the stepper motor pins control pins). I don’t know if this is what is supposed to happen, but I found it odd that one pin didn’t toggle while the other three did.
  • I’ve done the RAM test using closed-apple open-apple control reset and everything appears to be fine there.
  • I do not recall mis-inserting the 20-pin bus to the internal drive so I do not think the drive's 74LS125 is busted, especially since both drives are acting the same (unless my initial error blew both of them simultaneously.

I think my only option now is to wait until I get back to school and then start probing components with the oscope until something looks wrong.

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Original Apple IIc

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1978AppleII's picture
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Joined: Jul 5 2015
Posts: 194
Re: IIc Disk Drive/IWM problems

Hmm just for grins - have you tried another drive?

Or have you tried plugging those drives into another computer and verifying everything is good? I am wondering about the electronics on the drives themselves, and wondering if perhaps that's where the problem is.

Good luck!

Jennifer

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Joined: Jul 28 2016
Posts: 2
Re: IIc Disk Drive/IWM problems

Unfortunately, I don't have an other drives and I don't another vintage computer to test these ones with. I think my school has an Apple II on display somewhere, so I might just have to wait until I go back to school and coax my CS professor into letting it borrow it for 20 minutes.

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Original Apple IIc