Varispeed 7300 fans

[Bill Mayhew]

I believe the fan itself does the temperature sensing.  The power
supply does, of course, have a Klixon thermal cut-out.  Apparently
the power supply can still get pretty darn hot under fault
conditions because I have heard more than one horror story about
melted 7300 cases.

Not all 7300s and 3B1s have the same fan arrangement.  Some early
7300s have two fans, while most 3B1s have only one fan in the
cut-out behind the power supply.

The common collective Usenet wisdom is that one fan is better than
two beccause the air flow pattern is supposedly better with a
single fan.  A number of people have replaced the 12v DC operated
fan with a line oeprated AC fan.  A little load is taken off the
power supply, but rewiring and splicing into AC leads inside the
machine would be necessary -- do at your own risk.  I stuck with
the DC fan.

I have a Radio Shark temperature controller ($19.95) probe stuck in
the fan grille of my machie.  At the moment, the exhaust air is
about 90.3 F with 2 meg RAM, Voice Power, and Miniscribe 6085.  I am
considering updating my reboot sanity timer to monitor the overtemp
output from the Radio Shark module to force the 3B1 to shut down if
the fan fails suddenly.

==Bill==
-- 

Bill Mayhew  Northeastern Ohio Universities College of Medicine
Rootstown, OH  44272-9995  USA    phone: 216-325-2511
wtm at uhura.neoucom.edu   ....!uunet!aablue!neoucom!wtm