From: dnichols@ceilidh.beartrack.com (Don Nichols (DoN.))
Newsgroups: comp.sys.3b1
Subject: Re:  More info about my troublesome 3b1
Date: 14 Sep 92 01:15:52 GMT
Distribution: na
Organization: D & D Data


	I did a separate followup to the article to which this is a reply,
but there were some points in this one which I wanted to address separately.

In article <1992Sep11.103144.1@orion.yorku.ca> haroldt@orion.yorku.ca writes:
>Greetings:
>
>  (Disclaimer:  What follows is an opinion.)
>
>In article <1992Sep10.214017.1066@umbc3.umbc.edu>, hybl@umbc4.umbc.edu (Dr. Albert Hybl (UMAB-BIOPHYS)) writes:

	[ ... ]

>  I would not recommend that you run the machine open without some
>modification.  See below.

	I agree here, except as a stress test to isolate marginal components.

	[ ... ]

>  My 3B1 is now mounted vertically inside a small stereo stand with
>a $10 125V (self powered, not drawing from the already underpowered 
>3B1) fan.  The fan blows accross the disk drive and power supply (on
>the bottom of the stand), and up past the cpu and memory.  The top 
>metal plate is removed.  

	One thing about this that is perhaps not the best choice, but with a
strong enough fan is still no problem.  Generally, good practice has the air
flow cooling the rest of the machine first, and the power supply last, since
it can be expected to be at the highest temperature, it can better transfer
heat to an already warm airstream.  The 3B1's design does this, with the air
sucked in around the edges of the box, flowing across the cpu board's top
surface, up through the slot behind the disk drives, past the power supply,
and out the back.  My Sun 3/140 is designed with the card cage on the
bottom, an air filter on the input grill on the bottom (inside the floor
stand which allows the tower-style mounting), then through the card cage,
then through a bank of four fans in parallel, and finally through the power
supply on top.  There are strong warnings about not putting the power supply
end on the bottom.

	Since the board is on edge in your system, and there are not too
many auxiliary heat sources, natural convection will be aiding you, though
the power supply heat will be carried past the rest of the system (as will
the disk drive heat).

	[ ... ]

>days the box would just lock up.  Neither problem occurs now.  The 
>stock fan is not being used which frees up just a bit more juice for
>the rest of the unit.

	I don't even run the hard drives at all from the power supply in my
7300.  Both drives are external, and the 5V that went to the drive now goes
into an optically-isolated AC solid-state-relay, which turns on the input
power to the drive's power supply.

>> seems to be working well and there was no indications of
>> overheating when the shell was closed.  This suggests that
>> it is probably not a temperature-sensitive problem.  It may
>> be related to a crimped cable or poor grounding.

	The crimped cable (I missed answering this in my previous followup)
would not generate panics unless it was shorting out the +12V to the video
monitor.  That would either shut down the machine totally, or zap some video
driver circuitry, so that you would see nothing on the monitor.

>  I would agree.  The 3B1 has a thermal switch for the fan so 
>you would notice the fan running at full speed before any thermal
>problems occur.  I'm contemplating connecting the thermal switch to 
>some indicator or perhaps software that can shut the box down if the 
>temperature stays up too long.  Any ideas?

	This sounds like an excellent idea.  I could use the 12V to the fan
(with a threshold detector circuit) to turn on an alarm light (and perhaps a
Sonalert), and see if I wind up shooting my machine when it starts screaming
about the heat. :-) I do know a friend who has a PC-RT running their
unix-clone (AIX).  The machine shuts down untill the power is removed for
around 30 seconds if the power supply overheats.  When he goes away in the
summer, the system shuts itself down and I get no netnews or email for a
week (except at work).
>
>> The loose ground wire must have been like using a two prong
>> adaptor plug to defeat the grounding prong.  COULD or DOES
>> POOR GROUNDING CAUSE PANIC PROBLEMS?  COULD INTERMITTENT
>> CONTACT BETWEEN COMPUTER AND GROUND CAUSE PROBLEMS?
>
>  Any time that wire connects or disconnects, there will be a small
>change in Voltage and a definate change in the overall Capacitance.
>In other words, Yes.

	That is one possible cause of his problems.  I also mentioned to him
that it could be from oxidized contacts on the Power supply D.C. connectro,
and what to do about that.  (If he disturbed the connector - and it might
not be possible to lift the upper cover without disturbing it), it could
have broken the oxide film temporarially, by removing side stress on the
heavy duty ribbon cable, and moving the connector to a different area of
mating surface.  Thus, his problems may recur shortly after re-assembling
the machine, if this is the case.

	Good Luck to all
		DoN.

-- 
Donald Nichols (DoN.)     | Voice (Days): (703) 704-2280 (Eves): (703) 938-4564
D&D Data                  |  Email: <dnichols@ceilidh.beartrack.com>
I said it - no one else   |         <nichols@nvl.army.mil>
	--- Black Holes are where God is dividing by zero ---
Newsgroups: comp.sys.3b1,comp.sys.att