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From: nic@marque.UUCP
Newsgroups: comp.sys.att
Subject: Re: Weird 3b1 fan behavior
Message-ID: <1945@marque.mu.edu>
Date: Mon, 30-Nov-87 09:00:51 EST
Article-I.D.: marque.1945
Posted: Mon Nov 30 09:00:51 1987
Date-Received: Wed, 2-Dec-87 04:59:34 EST
References: <21740@ucbvax.BERKELEY.EDU> <313@bilanc.UUCP> <624@pttesac.UUCP> <626@pttesac.UUCP>
Reply-To: nic@marque.UUCP (Nic Bernstein)
Distribution: na
Organization: Marquette University - Milwaukee, Wisconsin
Lines: 61
Keywords: UNIXPC 3B1 fan power

In article <626@pttesac.UUCP> vanam@pttesac.UUCP (Marnix van Ammers) writes:
>In article <624@pttesac.UUCP> robert@pttesac.UUCP (Robert Rodriguez) writes:
>>Anyway, up until the repairman did this, my fan had *never* changed speeds.
>>But, you guessed it, now it does it about once an hour.  Seems to go into
>>overdrive and the air being fanned out is pretty warm.
>>
>>This raises some interesting questions, maybe some AT&T guys can answer.
>>
>Yes, it does raise very interesting questions.  You and I got
>our 3B1's at the same time.  I've added a EIA/COMBO board with
>1.5 Meg on it and a DOS73 board.  My far has only been at one
>speed since day one.  If we have dual speed fans, I would expect
>mine to have changed speeds after adding those two boards.
>
>Maybe I somehow have a newer issue fan which runs only at the
>single, higher speed?
>
>I would like to know for sure that my 3B1 will shutdown safely
>if my fan stops.  Someone in the know please enlighten us.
>
>Marnix
>----
>-- 
>Marnix (ain't unix!) A.  van\ Ammers		Work: (415) 545-8334
>Home: (707) 644-9781				CEO: MAVANAMMERS:UNIX
>WORK UUCP: {ihnp4|ptsfa}!pttesac!vanam		CIS: 70027,70
>HOME UUCP: pttesac!Marnix!vanam 

	Well this has gotten out of hand in my mind so, just to add to the
confusion, and maybe a possible solution...
	I have had, for some time, a friend with an original PC7300, and
yes he paid the original retail ( less about 10% ).  This unit has TWO
fans, one on the right side of the case in the rear, and one on the
left side.
	For about the first year, or so, the fans ran at the same slow
speed.  After that, they started running faster occasionally.  My
friend removed the case and cleaned out the accumulated dirt.  He was
very precicse about this (anal retentive) and removed all accessory boards
(memory) and used pure spray freon (tuner wash) to remove all traces of
dirt and grime, returning the unit to factory new condition.  He ALSO
CLEANED OUT THE FANS!  This unit returned to factory new quiteness.
However, he has to repeat this cleaning every 6 months or so ( he
does this for obvious reasons, not to quite the fans ) or the fan speed
up returns.  Neither he nor I have tried to figure out if the speed
change takes place in the power supply or if the fans themselves are
two speed.  It might pay to see if both fans speed up, be he hasn't
paid any attention and thats pretty subjective. 
	The service manual mentions only constant voltages of +5, +12
and -12 volts.  This seems to imply that the fan speed up is, in fact 
a quality of the fans themselves.  The manual also mentions that the
supply is both overvoltage and overcurrent protected and will shut
down totally in case of a short, etc.  The service manual also reccommends
using the fans as a trouble shooting tool as they will not run if the
supply is down.  You can disconnect everything, and if the fans run, then
there is a shorted device in the system (wait a few seconds for the supply 
to come up as there are delay circuits built in that will remain engaged after 
a short).
	This brings up a possible solution.  Is it possible, or practical,
to add a second fan ala the PC7300?  The service manual lists a "Fan
Assembly Spares Kit" Com Code 403865272.
						- Nic