Needed: 1 IBM 8" alignment disk.

From: John B <>
Date: Mon Nov 29 19:48:04 1999

-----Original Message-----
From: Tony Duell <>
To: Discussion re-collecting of classic computers
Date: Monday, November 29, 1999 9:40 PM
Subject: Re: Needed: 1 IBM 8" alignment disk.

>> It isn't alignment as I can manually move the head very slightly back and
>> forth which does affect the data coming into the controller assembly but
>> does not help it find the actual sector... Therefore, hardware or an
>> adjustment
>> I would like an alignment disk so I can use "their" tuning procedure to
>> this drive work quickly. It has a number of adjustments including :
>> window, gap, etc...
>Most alignment disks do not include such tests (I am not saying that the
>IBM one you asked for doesn't). They're just raw drive alignement disks
>with catseye patterns for aligning the radial position, an index timing
>burst, etc.

I hear you. This particular drive claimed it did.

>If you think there's an electronic problem then you don't really need an
>aligment disk. Start with the spindle speed, which I assume is right
>since it almost certainly uses a mains-powered induction motor. Still, it
>can't hurt to check that the index pulses occur at the right frequency.

That's all working fine... It's controller has a serious status system in it
where it monitors disk spindle speed, etc...

>They'll be a master clock, probably also used for writing. Check this
>with a 'scope or frequency counter. If it's incorrect, find out why.

One master clock.. 1Mhz, good.. A board dedicated to "data timing".

>Then take a formatted disk (format one yourself on your old CP/M machine
>if you have to ;-)). Read a sector continously. Display the off-disk data
>on one trace of a 'scope and the read clock on another. Does the read
>clock seem to be the right frequency? Is it locked wrt the data? If not,
>look at that read PLL (or whatever it uses).

Good idea on the CPM unit. I rarely use/see one so I will format one and
start that way.

>Index timing is either very important (if, for example, the controller
>expects to see an address mark as the first thing after an index pulse)
>or not at all important at this stage.

Not there yet.

>At this point you should at least be recovering data bits from the disk.
>So if it still can't find a sector, find out why not. Can it not find an
>address mark at all?. Or can it not find the header you're asking for.
>This is likely to be a digital problem. As I don't have schematics for
>this unit I can't comment any further.

It can't find a sector *most* of the time.. Once in a while I can get it to
read and display a sector correctly... The rest of the time it is in an
infinite loop.

What bugs me is sometimes I can read a sector with a good CRC and the data
is correct... probably *another* bad solder joint... this box has been
filled with them so far.

Thanks for the CP/M idea.

Received on Mon Nov 29 1999 - 19:48:04 GMT

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