ST506/412 failure modes? (in this case, an IBM 0665)

[Jules Richardson]

On 10/12/2015 01:58 PM, tony duell wrote:
>>
>> This may be forgotten knowledge - or perhaps more likely, something that
>> was never known in the first place - but are there any typical failure
>> modes of ST506/412-type drives (beyond the obvious mechanical damage
>> between heads and platters)?
>
> For the genuine original ST506 ST412, etc there is a very annoying failure of the
> hall effect device in the spindle motor. Annoying becuase the motor is on the
> outside of the HDA, but it is impossible to get to the hall device to replace it.
>
>> In this particular instance, I've got an IBM 0665 30MB drive in a Compaq
>> which spins up, bounces the heads around a little, then causes the machine
>> to issue a fixed disk failure at boot time. This is an embedded servo drive
>> with a voice coil, not a stepper type.  Oddly enough, it passes Compaq
>
> I am sure you know this, but there were ST412-interfaced drives with a
> separate servo surface.

I knew that once... it had decided to leave my brain, however :-)  I 
suppose this drive is probably old enough that it does indeed have a 
separate servo surface; the embedded kind doubtless came a little later.

>> diag's spare cylinder read/write tests, but fails the seek test. I've not
>> tried a LLF yet because I was interested in trying to salvage whatever data
>
> My first guess is that it is losing the servo signal at some point. Possibly
> due to platter damage. Do you get any nasty noises as the heads fly to one
> side or the other and then re-seek to the right track?

No, it sounds reasonably happy - no nasty grinding or screeching noises 
that often go with head damage.

Do these kinds of drives suffer from information disappearing over time? 
Not corruption as such, but the stored signal simply weakening?

cheers

Jules