Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!blackbox!cbradley
From: cbradley@Busl.COM (Chris Bradley)
Newsgroups: comp.sys.next
Subject: "Reversed fan problem" -- serial no. ranges
Summary: After S/N AAK0004000 (Sept. 28, 1989) they're ok
Keywords: fan dust cube 68030
Message-ID: <1990Dec7.002527.358@Busl.COM>
Date: 7 Dec 90 00:25:27 GMT
Sender: news@Busl.COM
Followup-To: comp.sys.next
Organization: Businessland Advanced Systems
Lines: 60

Over the past several months, a number of messages in this newsgroup
have mentioned that having a system unit fan that blows the wrong
way may increase the chances of dust accumulation inside the
magneto-optical disk drive in a NeXT Computer.

In the first production-runs of the NeXT Computer, the cooling fan
operated in a reverse direction from that of later units.  In these
early machines, the fan drew cool air inwards -- mostly through
the optical drive slot in the front of the cube -- and exhausted
the heated air through the fan grating in the rear of the system
unit.

Drawing air in through the optical disk slot allowed for the
accumulation of dust inside the magneto-optical drive, which has
been blamed for the early failure of some OMD-1 drive units.  In
a few cases, it seems that the problem was aggravated by leaving
an optical disk in the drive for long periods of time: several
weeks or months.  

In all cases, the environment appears to be the most important
factor.  If you leave your cube on the floor, or if the items in
the surrounding area seem to quickly gather a surface layer of
dust, then you should take precautions.

NeXT redesigned the cooling system to reverse the airflow and to
add more ventilation ports to the cube, providing more air exhaust
routes than solely through the optical drive slot.

According to Ken Jochims of NeXT Computer, Inc., the last of the
"wrong-way fan" machines was shipped on or about September 28,
1989.  The serial number of the last "wrong-way fan" machine was
in the neighbourhood of AAK0004000.

You can test your machine to see if its fan blows the "right" way:
take a small piece of paper and place it against the fan grating
on the rear of the system unit.  If the indrawn airflow causes the
paper to stick against the fan grating, then your cube probably
has the new airflow system.  If, instead, the paper blows away from
the fan grating, then your machine is probably using the older
airflow design.

For users with older cubes that employ the original cooling design,
NeXT is providing a head cleaner, a disk cleaner, and a dust filter
for the optical disk drive.

	Part #  Price   Description 
	=======	=====	==========================================
	S3901-p $60     Canon OM-HC1 Head-Cleaning Kit 
	
	S3902-p $15     Canon MO-CK1 Magneto-Optical Disk Cleaning 
			Kit 
			
	S3900-p $10     MO Drive Filter

These items are available at NeXT Authorized Service Centers.
-- 
Chris Bradley			| "Nothing is more certain than incertainties; 
Businessland Advanced Systems	|  Fortune is full of fresh variety:
Dallas, Texas US		|  Constant in nothing but inconstancy."
cbradley@busl.com		|		-- Richard Barnfield 1574-1627