🚀 go-pugleaf

> 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.