Subject: troubleshooting an SA-400 disk drive

From: Eric Chomko <[email-masked]>
Date: Tue Jun 10 21:29:00 2003

I have been monitoring this new problem for a few days. Actually,
it first surfaced weeks ago, but I had zero time to look into it.

Anyway, I have a three drive Smoke Signal Broadcasting disk system,
in which one drive, 2 (last one on 0,1,2 chain), has this nasty whine
when
powered on. The other two drives work and sound fine.

The faulty one's driver motor never stops when powered on whereas the
other two do. The others must have the last one due to the terminator
which functioned correctly in the chain. I have managed to pull the bad 
drive and managed to get the two working ones to work with terminator
resister moved to drive 1. I put 2's (bad drive) large electronics board
onto 1's drive mechanism and it works fine. That leaves 2's drive
mechanism
as being bad; either the small circuit board or the drive motor.

Also, when 2 is selected the red LED does light up, but no diskette can
be read.

Something is forcing the drive motor to stay on or the drive motor
itself is defective.

Any suggestions? I plan to put 1's (good drive) small electronics board
onto 2's drive mechanism to see if the drive motor control or the drive
motor itself is bad. Left my soldering iron at work. :^(

---

From: Peter Turnbull <[email-masked]>
Date: Wed Jun 11 02:25:45 2003

On Jun 10, 22:23, Eric Chomko wrote:
> other two do.

Sounds like the motor control board is faulty.

> The others must have the last one due to the terminator
> resister moved to drive 1.

The terminator should be on whatever drive is last in the chain (the
end of the ribbon cable).

> I put 2's (bad drive) large electronics board

Motors sometimes burn out, but other faults are relatively uncommon.
 These motors normally have three or four wires; two are the power, and
the other(s) are the tachometer signal back to the control board; this
tells the control board how fast the motor is going.  The tacho may be
broken, but a faulty control board is more likely.  If one of the other
drives uses the same motor you could try swapping, which at least would
tel you whether its the control board or the motor itself.

The whine is probably because the motor is running far too fast, and
that is why you can't read a disk.  Don't let it run like this too long
or you'll damage the motor.

-- 
Pete						Peter Turnbull
						Network Manager
						University of York

---

From: Eric Chomko <[email-masked]>
Date: Wed Jun 11 07:31:00 2003

> Sounds like the motor control board is faulty.

I'll find out when swap the good board with the one on the bad drive.

> end of the ribbon cable).

Yes.

> tel you whether its the control board or the motor itself.

Yes, that is the plan. The motor has four wires.

> or you'll damage the motor.

Thanks.

Eric

---

From: [email-masked] (Tony Duell)
Date: Wed Jun 11 18:34:22 2003

> The faulty one's driver motor never stops when powered on whereas the

OK...

[...]

> as being bad; either the small circuit board or the drive motor.

The small circuit board is the spindle motor speed controller. It 
normally contains an LM2917 Tachometer IC and a few other components. The 
spindle motor has 4 wires -- 2 are for the DC (brush-type) motor, the 
other 2 are the AC tachometer generator. The frequency of the latter is 
measured by the LM2917 and used to control the spindle motor.

On this PCB there's a power transistor, often a darlington type. If this 
shorts (and it sometimes does) you get exactly the problem you're seeing. 
The spindle motor runs at full speed all the time (hence the whine)

> Also, when 2 is selected the red LED does light up, but no diskette can

Not suprising. The motor is running far too fast.

> Something is forcing the drive motor to stay on or the drive motor

I can't think of a fault in the spindle motor that would cause this. If 
the tacho winding goes open circuit (_very_ uncommon), the motor will run 
at maximum speed when turned on by the controller, but the controller 
will be able to stop the motor.The fact that the motor runs all the time 
implies a fault on the control PCB (the 'small circuit board').

-tony