12 Apr
2010
12 Apr
'10
7:01 p.m.
On Mon, 12 Apr 2010, Tony Duell wrote:
The drive is not particularly small, BTW. This is a beast of an 8" drive
mechanism with five platters and a voice-coil positioner.
I removed the resistor and it does not try to spin. Traced things out as
best I could (it's a three-layer board with limited visibility to the
interior plane). The +24V input runs directly and almost solely to the
armature of one SPDT relay contact set. The NO position goes directly to
the motor / armature connector and the NC position goes nowhere. This
gives some support to my theory that the resistor and associated circuitry
is there to limit inrush current. I think this relay is supposed to pull
in rather quickly and feed power directly to the motor.
The downstream leg of the 10-ohm power resistor goes to a 2SD768 power
device and I'm having a lot of trouble following it from there. I think
your guess about a regulator for the 12V circuitry is probably correct.
Steve
--
Has anyone on the list seen or work with one of these? I received a
Morrow M-20 8-inch hard disk along with my N* Horizon and found the
Memorex 102 disk mechanism inside (what a beast!).
At initial power-up, a 10-ohm 5W resistor near the power connector let out
a puff of smoke (the drive was in the process of spinning up). I killed
power and started checking components carefully. There were no ominous
readings across the 5V logic power rails and I traced things out enough to
determine that this resistor was between the +24V power input and whatever
lies downstream (probably motor servo).
It would be worth knowing what that resistor feeds. The obvious things to
need the 24V rail are the spindle motor and positioner (which could be a
stepper nmotor in an old/small drive like this, or it might be a voice
coil). I would also suspect that the 24V line is regualted down to 12V
for some of the analogue circuitry.