From: dnichols@ceilidh.beartrack.com (Don Nichols (DoN.))
Newsgroups: comp.sys.3b1
Subject: Re: More info about my troublesome 3b1
Date: 14 Sep 92 00:55:30 GMT
Distribution: na
Organization: D & D Data

In article <1992Sep10.214017.1066@umbc3.umbc.edu> hybl@umbc4.umbc.edu (Dr. Albert Hybl (UMAB-BIOPHYS)) writes:
>
>This posting is in response to a mild scolding from a
>respondent:  "It would have been nice to have an indication as
>to which version of O.S. you are running.  (B.T.W. The [panic]
>messages vary with the version of the O.S.)  Also, are you on a
>7300 or a 3b1?  How much memory on the CPU card?  Any extra
>memory?  Any other cards present?"

	Your following is an excellent listing of the important details.

>There are no cards in the expansion slots.  There is 2Mb of
>memory on the motherboard.  I am running 3.51m.  The disk
>cntr is WD1010 and the motherboard is P3...P5.  The machine
>was sold to me as a 3b1.  It has the hump and a full height
>HD with 67 Mb of memory.  The power supply is Model PS 1569
>that says it is a 7300 (3B1s use model PS 1610-1).  Reading
>the FAQ description of the differences:
>
>"The 7300 machines featured 512k RAM on the motherboard with a
>10 or 20MB disk.  The later 3B1 machines had 1M or 2M on the
>motherboard, and came with a 40 or 67MB disk. ... The 3B1 also
>has a heftier power supply."  ARE THERE ANY OTHER DIFFERENCES
>BETWEEN A CPU MOTHERBOARD OF A 3B1 AND A 7300 BESIDES THE AMOUNT
>OF MEMORY?  I assume not.

	A 7300 cpu card will have two power connectors for the drives (one
for the floppy, and one for the hard drive).  The 3b1 provides power for the
hard drive through wires directly from the power supply, without a side trip
through the cpu board.  I have not explicitly checked a 3B1 motherboard for
the presence of the four solder pads in a row for the hard drive similar to
the floppy, but if it was a 7300 cpu board (with memory added) you would
either have the old connector and wires still present (and perhaps taped up,
as in the converted machine which I got at the hamfest today), or they would
probably show signs of the wires having been unsoldered.  (This would
include the holes being empty after being cleaned by a solder sucker, since
the machine was wave soldered, the holes would normally be filled with
solder, even if nothing was there.)

>It seems that I have either an underpowered 3b1 or a memory enhanced
>7300.  I plan to add a 2Mb memory expansion board and a STARLAN
>board.  WILL THE PS-1569 POWER SUPPLY BE A PROBLEM?

	Check that the power supply has been modified to route power
directly to the hard drive by soldering wires to the holes adjacent to the
D.C. power connector.  While you are there, also check for signs of
overheating of any of the pins in the D.C. connector on the ribbon cable
from the cpu.  If this has been the case, then the plastic is usually
discolored (browned) where that pin is.  A frequent source of hard disk
problems, panics, etc, is one pin in the D.C. connector getting oxidized,
and introducing reduced voltage to the cpu board, and variations in the
voltage, which can cause some *very* strange malfunctions.

>Since my first post I have had several panic messages,
>one with trap vector 11 followed by a "Double panic" with
>trap vector 1 after which the system did not reboot

	"Double Panic" means that the kernel hit a second panic while trying
to deal with the first one, and just gave up entirely.

>and the monitor only displayed the green screen:
>--__--__--__--__--__   etc.to the end of a line 
>--__--__--__--__--__
>--__--__--__--__--__
>--__--__--__--__--__
>The lines on the screen are very close together and the pattern
>fills the screen. (The -- are true lines not dashes.)
>They could be called shallow square-wave patterns that fill the
>whole window. 

	Possibly the result of some glitched program code writing
alternating 01 patterns into the video memory.  It would have to be kernel
code (or a corrupted MMU register) to allow writing to the video ram
directly.  If you are getting power supply glitches, anything is possible.

>I opened the machine again to expose the FD, HD and Power Supply
>and noticed that the GREEN ground wire from the switch block
>to the back corner of the power supply was held by a loose
>screw!  It was not disconnected just loose.  I tighted that screw
>then examined the other wires and cables.  The cable to the monitor
>has an indentation caused by the HD and the screw that should hold
>it to the frame on the left side was missing.  The other wires
>look OK.

	It probably would have been better without the wire making any
contact at all. :-) Intermittent connections (even to ground on the input to
the power supply), can generate strange bugs.

>Without closing the machine, I reattached the keyboard and turned
>the 3b1 on.  Two pencils separate the keyboard from the
>metal platform where it would usually be when packed.
>The monitor faces the ceiling with space allowed for
>the fan to function.  THE MACHINE BOOTED AND HAS BEEN
>RUNNING SINCE--ABOUT 40 CONTINUOUS HOURS SO FAR.  I have run
>a number a tasks on the machine, including I/O via the floppy
>drive.  I'll start running the diagnostic disk to test the
>memory soon.

	I agree with the other poster that this should not be done as
standard practice, (though I consider it a form of stress test to find
marginal components, if any).  At this point, you should add some extra
airflow over the plate and power supply to avoid generating premature
failure of components like capacitors and the battery on the cpu board.  The
design of the box plus the cover is such that some of the air that exits via
the fan if forced to go through the box over the cpu and under the plate,
and sweep up behind/between the drives.  I consider short-term operation
with the case opened to be reasonable, but I generally try to button the
machine up after, perhaps, the time required to format and test a hard disk
drive.

>The metal plate below the keyboard is running warm.  The CPU
>is surely just as hot as when the hood is closed.  The fan
>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 impression that I got from your description was that the fan is
still in the top, and has simply been propped up enough to allow airflow
through the fan itself.  This doesn't really cool anything other than the
fan motor.

>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?

	Sure could.  It is more likely if you are connected to other devices
through the parallel or the rs232 ports, but it is possible in other cases
as well.  HOWEVER, another point to consider:  Did you disconnect the D.C.
connector to the power supply and open up the top before running these
tests?  If so, it still could be an intermittant (oxidized) contact on the
D.C. connector.  If you can get Cramolin (there aren't many dealers, since
they seem to have rather overkill in stocking requirements), you should
treat the power connector with it.  (Use Cramolin Red (R5), since it both
cleans and protects.  The Blue is primarially for protection of already
clean contacts.  If you cant' get that, get some other contact cleaner,
spray (or apply in some other manner), and then slide the connector on and
off several times to break down the oxide film.  I did this (with Cramolin)
to the machine which I just got, even before powering it up.  The connector
showed no localized browning on that one, and now I don't expect it ever to.

	I hope that your problem stays away.

	Good Luck
		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>
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Newsgroups: comp.sys.3b1