> hmmmmmmm - interesting thing is - that I don't think there's that much stuff -
> the system is configured as follows
> 
> 1 x RD53
> 1 x TK50
> 1 x RD disk controller
> 1 x TK50 controller
> 1 x KA630 motherboard
> 1 x 4 Mb memory card
> 
> That's it so far - as an experiment - I tried to get one of the RD53's to spin
> up at a constant speed on a power supply from an IBM RT Model 135 (Read as
> *HUGE* power supply) - and it exhibited the same behavior - spun up - and immediately spun back down.

I don't think that your system has too much stuff on it.
My system (BA23 also, 385 Watts) has RD53, RD32, RX33, and TK50 plus
2 additional memory boards and I've never had problems like that.

Has your RD53 (or both of them) been out of use for a long time ?

Ciao,
	bertram

PS: I've appended some news-articles on this subject I collected 
    from comp.sys.dec and related groups ...

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> Many disk drives suffer from spin-up problems.  The standard fix is to
> remove the drive from the chassis and sharply jerk the housing around
> the spin-axis of the disk.  Since the disk has some inertia, this will
> spin it enough to break the friction in the bearings.  Reinstall the
> disk drive and power up the machine.  The disk should spin up now. 

Be careful not to confuse stiction with drive-self-diagnostic failure.
An ST225 or ST251 classically gets hit with stiction - the heads stick
to the platters and a good twist can free them.  On the other hand, the
Micropolis 1325 (and 1335), an RD53 (with R7 jumpered) will have no problem
spinning up.  It spins up, self-tests and spins down.  A local hardware
person here conjectures that as the drive ages, the windings deteriorate
and the apparently extensive current sensing circuitry on these drives
detects something out of spec at spin-up and shuts the drive down.







I've found RD53s to be either 1) completely reliable or 2) utterly
faithless when it comes to spinning up and staying spun up.  I have
eight here, and the only failure I have seen one adopt relates to
spinup.  They'll either spin up, decide they're sick and spin down
immediately, or spin up, fool you by running a while, and then spin
down and back up almost immediately.

I have no problems other than this with the drives.  A good one is
quite reliable.  A bad one isn't worth the fixing, as all that I
have had fixed started doing the same thing shortly after coming back
from repair.

(I would no more try to "break loose" a drive by spinning it around
 the platter axis, than I would pour sand into my gas tank.  Disk
 heads are not designed to move backwards when sitting on the platter,
 are not stressed for that, and break when you try it.  I know.  It
 was expensive.)

/s/ Bruce R. Mitchell
    Editor Emeritus, "The Multi-Tasker"
    US DECUS RSX SIG



In article <1993May14.023933.1@vax2.winona.msus.edu> wnimhack@vax2.winona.msus.edu writes:
>
>I have no problems other than this with the drives.  A good one is
>quite reliable.  A bad one isn't worth the fixing, as all that I
>have had fixed started doing the same thing shortly after coming back
>from repair.

A common problem as there are a lot of shady repair depots.  You think you're
saving a few bucks, but if they can't spot a glaring fault easy to fix, all
they do is clean it out, briefly make sure it seems to work, but not long
enough to know/care, and then put a repaired-unit tag on it, and send it
back to you.

You have to send the unit out with an explicit complaint such as:

Unit will not stay spinning for as long as an hour.  Ensure unit passes 
long-term spinning tests before leaving repair facility.  If unit is returned
to us with the problem still present we will just return it to your repair
facility and expect to be reimbursed for the unnecessary shipping.

Once they see the notice, they'll think twice about doing the equivalent
of the crooked auto repair shop that charges for a tuneup and just raises
the idle.

cjl





I have a disk which exhibits the problem of spinning up then down,
then up, then down in about 4 second cycles.  When I replaced the
board with one from another disk, the disk was fine (the symptom
travelled with the board).

I have also tried the 'spin case around disk axis' trick and it
has worked for me.  I do, however, try to be carefull about which
way I spin the casing so that at least the heads still move in the
direction they are supposed to.




> That's what must be wrong with one of my RD53's.  It spins up, gets
> to what sounds like operating speed, spins partially down, then back
> up, then down, up, down ... on about a 4 second cycle.

The spin-up -> spin-down I've seen is one-shot.  The drive shuts itself down. 
Your drive's behavior reminds me of a drive that I accidentally used a DEC
mounting baseplate that has a lot of metal and fingers - I was stupidly
shorting some of the pins on the drive controller board and got erratic
behavior like what you describe (although not so well synchronized).
(I later encountered a DEC installation and discovered the sheet of paper
they use to insulate the controller board)


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