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I'm looking for resources and/or advice.

What problems with a IIc could be causing either the internal or external drive to make this horrible grinding sound? It's different than the usual startup clicking sound of a II finding home on the head, which the computer also makes.

I've swapped out the internal drive with a spare, and the internal power supply with a spare, but all three drives (2 internal, and an external) make this sound when accessing any disk after about 20 minutes of operation, with there being no bad sounds for the first 20 minutes or so.

I've got a logic board and internal power supply re-cap kit on the way if it's either of these, but I'm curious if there's something else more common that causes this kind of issue.

2 Answers 2

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The startup sound on the Disk II is produced by a simple ROM routine which repeatedly strobes addresses $C0E7 to $C0E0 in descending order with a fixed amount of delay between. Each time the whole sequence is repeated the drive head will move two tracks outward unless it's against the end stop in which case it won't move any more. This approach to moving the head outward will work, but it's a bit slow. The head can be stepped much faster if the controls are operated in a different sequence, with more complicated timing, and both DOS and ProDOS exploit this. Normally those operating systems wouldn't move the head against an end stop, but if they have trouble reading a disk and can't read track label markers from the disk, they will run the head to the end stop and then move it inward by the expected number of tracks, to ensure the head is actually where it's supposed to be.

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    This isn't the startup sound - this occurs well after startup. The information about DOS/ProDOS exploiting faster stepping is helpful though.
    – nboyko
    Sep 22, 2023 at 19:58
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    @coneypylon: The grinding sound is the ProDOS or DOS (I think ProDOS) head-homing routine, which is faster than the startup clicks but conceptually the same.
    – supercat
    Sep 22, 2023 at 20:21
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    Got it - thanks! So it seems like for some reason long after startup, DOS (in my case) is having trouble with finding data, so it's repetitively homing. That's a helpful place to start, at least!
    – nboyko
    Sep 22, 2023 at 21:47
  • This answer was the most helpful in ultimately finding the problem, which turned out to be a bad IWM chip.
    – nboyko
    Oct 20, 2023 at 20:04
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The sound you hear is when DOS detects an error with reading/writing the disk and is trying to re-align the drive head by pushing it to the far ends. This is a pretty normal behavior, but usually indicates that your disk might be corrupted or the drive has a problem.

Seeing how you have a DOS loaded (whether DOS 3.3 or ProDOS) since you're able to type SAVE WHATEVER and the disk drive spins, I'm assuming you booted from a good disk, or at least one that was good enough to load DOS. If you're trying to save to the same disk, it might be partially corrupted or no good. If you're trying to save to a different disk, then that disk might be bad and you should try a different one.

When talking about floppy disks being "no good", I'm referring to how the floppy disk you're using is most likely 30+ years old and the idea that they will degrade over time. Depending on how it was stored all these years, might be partially disintegrating, could have had mold or something else which causes it to not hold a good magnetic signal pattern anymore. As well, you should make sure that you're using one that is labeled as DS/DD (the 'DD' part referring to Double Density; a 1.2MB HD 5.25" IBM disk might not work very well).

To see if the disk is physically bad, you can inspect the disk by expanding your fingers like a 'V' in the center hole and carefully spin the disk while looking in the oval window. You should see a consistent brown/gray color and NOT see any spots or significant streaks. If you do see spots or discolorations, most likely the disk is no good anymore and will not work. If you don't see any particular problems, it might just be that the disk needs to be reformatted/erased.

If you can reformat the disk and the same problem happens again, then it might be your disk drive. It isn't too common for Apple //c drives to be out of alignment, but it is a bit more likely that the disk heads are dirty. If you're comfortable with opening up the disk drive again, the heads can be cleaned with Q-Tips and isopropyl alchohol.

That being said, a recap wouldn't hurt, but seeing how you got this far it is less likely to be the result of a bad cap.

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  • It sounds like it could be the alignment. I'm able to save and load consistently fine for the first 10-20 minutes the machine is on (thus booting into DOS), but the same disks work poorly after that time, so that's why I was thinking it could be a cap issue, or a heat issue. What software would you recommend for aligning?
    – nboyko
    Sep 22, 2023 at 19:56

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