Re: CBM900 hard disk timeout

From: Michał Pleban <>
Date: Sat, 18 Oct 2014 17:46:56 +0200
Message-ID: <>

Martin Hoffmann-Vetter wrote:

> The 74LS14 has a schmitt trigger input. So it would be better to replace it with a real 74LS14 instead a 74LS04!

Yes of course. I used a '04 because I didn't have a '14 in stock. I have
since then purchased a '14 but the controller operation did not change.

> So it's possible the pcb from the MiniScribe disk isn't okay. You have checked the stepping logic. At this time you miss the pulses at the INDEX line. Is this signal present with the working disk? If you see the pulses, you can analyse where the signal are generated. This signal must be pulse once at one rotation!

No. I have scoped the ST-4096 I am currently using, and it also does not
seem to send the INDEX signal. So apparently it's not the problem for
the controller.

> The MiniScribe 3650 and 3675 ( has an error code 4 for the case "Index pulse not detected during spinup". And the code 4 means:

Yes. I have seen this error being flashed when the drive fails to spin
on powerup, which it does quite often. Combined with a screeching sound
it generates on some occasions when spinning, I think this disk just
needs to be written off :-)


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Received on 2014-10-18 16:00:04

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