🚀 go-pugleaf

bob@kc2wz.bubble.org (Bob Billson) writes:

> Hi net.world, I need your help!
> 
> I have a Micropolis 1325D hard disk (MFM, 71 meg).  Back in August when we we
> having our usual hot summer days, the 1325 start acting "weird".  The
> temperature got up to 95 degrees (F) in the room where I keep the computer.  
> to this point the 1325 has be very reliable.
> 
> On the first day of the hot spell I turned the computer on, the hard drive
> began to spinup; just as it reached the point where the heads would unpark, i
> started spinning down...uh oh!
> 
All drives experience weaker motor torque as the temperature of the 
windings increases. Also higher humidity or high temp with the same 
relative hum. will increase the head stiction from a "cold" start. 
However a "good" unit should overcome these difficulties and start up.
The spindown is automatically invokes if the RPM does not reach a certain 
speed threshold after a certain time. Each drive design is different, 
some are 3000 RPM after 20 seconds, etc.etc.  THis is done to prevent the 
drive from self damage due to excess wear in the LANDING ZONE at the 
inner cylinder park zone.

My question is does the drive take longer than "normal" to speed up 
ie would it normally reach full  speed  at the time when it fails to 
reach "RPM OK" on startup?
If it is taking longer to startup, then you may be able to increase power 
by adjusting your 12V supply to 12V +5% or +10% at the drive. THere may 
be a sag during startup.
The switching MOSFET transistors used for motor commutaion may be getting 
hot (lossy) and robbing power from your spindle during startup. If you 
can measure the voltage drop with a scope, this may be your units 
weakness.
PUT YOUR EAR TO THE DISK ENCLOSURE during startup. If it appears to be 
making "scraping, buzzing or any unusual sounds", then you are getting a 
WORN landing zone, and you cannot do anything to repair this. It is 
advisable then to reduce the number of power cycles on this drive to 
increase life time.  Normally 10,000 power cycles should be a minimum 
life of the drive. But occasionally, drastic reductions are caused by 
specs of contamination inside or many other reasons.

I had a weak motor on an old CDC Wren 40MB drive and it wouldn't start 
due to motor torque was less then head stiction., so I gently rotated the 
disk to help it start, then let it run. That worked on days when the 
humidity was high and it was idle for many days previously.  Frequent 
useage helped reduce this drive's problem. Some times I had to use a 
pencil eraser tip to push start the spindle to get it going.  Its well 
over 5 years old and still working, so I can't complain.

I don't know if Micropolis had any Rev level changes to improve this 
problem, but you could call the factory in the valley and report your 
model and rev. level and ask for customer support.

dino@inqmind.bison.mb.ca
The Inquiring Mind BBS, Winnipeg, Manitoba  204 488-1607