🚀 go-pugleaf

In article <C0AGzD.GtH@watdragon.uwaterloo.ca> kcwellsc@watdragon.uwaterloo.ca (Ken Wellsch) writes:
>> I have a pair of RD53s (real DEC-labelled RD53s) which I tried to put
>> on a DOS machine.  I pulled the R7 jumper and set the drive select to
>> 1, and managed to get one to format on the ST506 controller.  However
>> it then started to exhibit a strange behavior:  It won't stay spun up.
>> When power is applied it spins up to what seems to be close to full speed;
>> I think I hear the click indicating that the heads are being released;
>> but then it spins down again.
>> 
>> Same thing happened with the other drive even before I tried formatting
>> it.
>> 
>> What could I have done to these drives???
>
>You don't say anything about the history of the drives.  We here at U of
>Waterloo have loads of RD53's that have the same behavior.  Our hardware
>wizards have swapped the board portion among the drives from known working
>drives without success.  So my guess is you've received these drives with
>this condition (i.e. they did the same in their DEC equipment as well
>which maybe why you've now got them?)
>
>The current theory is this: these Micropolis 1325's and 1335's apparently
>have quite sophisticated current sensing circuits to monitor the motor
>load and such.  With time, the motor windings degrade and the current
>load exceeds the tolerance of the limiting circuit.  The spin-up spin-down
>behavior is the drive saying I am not working correctly.
>
>I've also heard about these puppy's having thermal troubles as well, they
>run for a while then spin down.  I think it may be a similar problem.
>
>Indeed as others have pointed out, they do draw a heck of a current normally
>as well -- 2.5A as +12V normally.

YES---- I agree!  I have several micropolis drives which were in PCs
which failed the same way.

Then, when I inherited a microvax with a micropolis drive, I installed
the OS (ultrix 1.1!) successfully, cycled the power, and had the drive
spin up and then down, I could have kicked myself.  Needless to say, I
wasn't that surprised.  Sometimes it works, sometimes it doesn't.  If you
get it spinning, don't shut it down!

So now I have 7 of these drives and it may be worth my time to figure
out how to fix them!  (if nobody else has).  My top prioity is
finishing my disseration, so the micropolis project will be on hold
for at least a month.  (So what am I doing reading news?)

If people have some dead drives to donate to me to experiment on, I
could use them.........